Collections
Meteor stores data in collections. To get started, declare a collection with new Mongo.Collection
.
Mongo.Collection
Summary:
Constructor for a Collection
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
name | String | The name of the collection. If null, creates an unmanaged (unsynchronized) local collection. | Yes |
options | Object | No |
import { Mongo } from "meteor/mongo"";
const collection = new Mongo.Collection(
"name",
options, // this param is optional
);
Calling this function is analogous to declaring a model in a traditional ORM (Object-Relation Mapper)-centric framework. It sets up a collection (a storage space for records, or "documents") that can be used to store a particular type of information, like users, posts, scores, todo items, or whatever matters to your application. Each document is a EJSON object. It includes an _id
property whose value is unique in the collection, which Meteor will set when you first create the document.
// Common code on client and server declares a DDP-managed Mongo collection.
const Chatrooms = new Mongo.Collection("chatrooms");
const Messages = new Mongo.Collection("messages");
The function returns an object with methods to insert
documents in the collection, update
their properties, and remove
them, and to find
the documents in the collection that match arbitrary criteria. The way these methods work is compatible with the popular Mongo database API. The same database API works on both the client and the server (see below).
// Return an array of my messages.
const myMessages = await Messages.find({ userId: Meteor.userId() }).fetchAsync();
// Create a new message.
await Messages.insertAsync({ text: "Hello, world!" });
// Mark my first message as important.
await Messages.updateAsync(myMessages[0]._id, { $set: { important: true } });
If you pass a name
when you create the collection, then you are declaring a persistent collection — one that is stored on the server and seen by all users. Client code and server code can both access the same collection using the same API.
Specifically, when you pass a name
, here's what happens:
On the server (if you do not specify a
connection
), a collection with that name is created on a backend Mongo server. When you call methods on that collection on the server, they translate directly into normal Mongo operations (after checking that they match your access control rules).On the client (and on the server if you specify a
connection
), a Minimongo instance is created. Minimongo is essentially an in-memory, non-persistent implementation of Mongo in pure JavaScript. It serves as a local cache that stores just the subset of the database that this client is working with. Queries (find
) on these collections are served directly out of this cache, without talking to the server.When you write to the database on the client (
insert
,update
,remove
), the command is executed locally immediately, and, simultaneously, it's sent to the server and executed there too. This happens via stubs, because writes are implemented as methods.
When, on the server, you write to a collection which has a specified
connection
to another server, it sends the corresponding method to the other server and receives the changed values back from it over DDP. Unlike on the client, it does not execute the write locally first.
DANGER
On Meteor 3.x and later using insert
, update
, upsert
, remove
, findOne
on the server will throw and error. Use the *Async
counterparts instead.
For example, instead of collection.insert(doc)
, use collection.insertAsync(doc)
.
If you pass a name to a client-only collection, it will not be synchronized with the server and you need to populate the collection "manually" using the low-level publication interface (added/changed/removed
). See added
for more information.
If you pass null
as the name
, then you're creating a local collection. It's not synchronized anywhere; it's just a local scratchpad that supports Mongo-style find
, insert
, update
, and remove
operations. (On both the client and the server, this scratchpad is implemented using Minimongo.)
By default, Meteor automatically publishes every document in your collection to each connected client. To turn this behavior off, remove the autopublish
package, in your terminal:
meteor remove autopublish
and instead call Meteor.publish
to specify which parts of your collection should be published to which users.
// client.js
// Create a collection called `Posts` and put a document in it. The document
// will be immediately visible in the local copy of the collection. It will be
// written to the server-side database a fraction of a second later, and a
// fraction of a second after that, it will be synchronized down to any other
// clients that are subscribed to a query that includes it (see
// `Meteor.subscribe` and `autopublish`).
const Posts = new Mongo.Collection("posts");
Posts.insert({ title: "Hello world", body: "First post" });
// Changes are visible immediately—no waiting for a round trip to the server.
assert(Posts.find().count() === 1);
// Create a temporary, local collection. It works just like any other collection
// but it doesn't send changes to the server, and it can't receive any data from
// subscriptions.
const Scratchpad = new Mongo.Collection();
for (let i = 0; i < 10; i += 1) {
Scratchpad.insert({ number: i * 2 });
}
assert(Scratchpad.find({ number: { $lt: 9 } }).count() === 5);
Generally, you'll assign Mongo.Collection
objects in your app to global variables. You can only create one Mongo.Collection
object for each underlying Mongo collection.
If you specify a transform
option to the Collection
or any of its retrieval methods, documents are passed through the transform
function before being returned or passed to callbacks. This allows you to add methods or otherwise modify the contents of your collection from their database representation. You can also specify transform
on a particular find
, findOne
, allow
, or deny
call. Transform functions must return an object and they may not change the value of the document's _id
field (though it's OK to leave it out).
// An animal class that takes a document in its constructor.
class Animal {
constructor(doc) {
_.extend(this, doc);
}
makeNoise() {
console.log(this.sound);
}
}
// Define a collection that uses `Animal` as its document.
const Animals = new Mongo.Collection("animals", {
transform: (doc) => new Animal(doc),
});
// Create an animal and call its `makeNoise` method.
Animals.insert({ name: "raptor", sound: "roar" });
Animals.findOne({ name: "raptor" }).makeNoise(); // Prints 'roar'
transform
functions are not called reactively. If you want to add a dynamically changing attribute to an object, do it with a function that computes the value at the time it's called, not by computing the attribute at transform
time.
WARNING
In this release, Minimongo has some limitations:
$pull
in modifiers can only accept certain kinds of selectors.findAndModify
, aggregate functions, and map/reduce aren't supported.
All of these will be addressed in a future release. For full Minimongo release notes, see packages/minimongo/NOTES in the repository.
WARNING
Minimongo doesn't currently have indexes. It's rare for this to be an issue, since it's unusual for a client to have enough data that an index is worthwhile.
Read more about collections and how to use them in the Collections article in the Meteor Guide.
Collection.find
Summary:
Find the documents in a collection that match the selector.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
selector | MongoSelector | A query describing the documents to find | No |
options | Object | No |
// Collection is an instance of Mongo.Collection
/** @returns Mongo.Cursor */
const result = Collection.find(
MongoSelector, // this param is optional
options, // this param is optional
);
find
returns a cursor. It does not immediately access the database or return documents. Cursors provide fetch
to return all matching documents, map
and forEach
to iterate over all matching documents, and observeAsync
and observeChangesAsync
to register callbacks when the set of matching documents changes. Cursors also implement ES2015's iteration protocols.
WARNING
Collection cursors are not query snapshots. If the database changes between calling Collection.find
and fetching the results of the cursor, or while fetching results from the cursor, those changes may or may not appear in the result set.
Cursors are a reactive data source. On the client, the first time you retrieve a cursor's documents with fetch
, map
, or forEach
inside a reactive computation (eg, a template or autorun
), Meteor will register a dependency on the underlying data. Any change to the collection that changes the documents in a cursor will trigger a recomputation. To disable this behavior, pass {reactive: false}
as an option to find
.
Note that when fields
are specified, only changes to the included fields will trigger callbacks in observeAsync
, observeChangesAsync
and invalidations in reactive computations using this cursor. Careful use of fields
allows for more fine-grained reactivity for computations that don't depend on an entire document.
On the client, there will be a period of time between when the page loads and when the published data arrives from the server during which your client-side collections will be empty.
Collection.findOne
Summary:
Finds the first document that matches the selector, as ordered by sort and skip options. Returns undefined
if no matching document is found.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
selector | MongoSelector | A query describing the documents to find | No |
options | Object | No |
// Collection is an instance of Mongo.Collection
/** @returns Object */
const result = Collection.findOne(
MongoSelector, // this param is optional
options, // this param is optional
);
WARNING
Client only. For server/isomorphic usage see findOneAsync.
Equivalent to find
(selector, options).
fetch
()[0]
with options.limit = 1
.
Collection.findOneAsync
Summary:
Finds the first document that matches the selector, as ordered by sort and skip options. Returns undefined
if no matching document is found.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
selector | MongoSelector | A query describing the documents to find | No |
options | Object | No |
// Collection is an instance of Mongo.Collection
/** @returns Object */
const result = Collection.findOneAsync(
MongoSelector, // this param is optional
options, // this param is optional
);
Async version of findOne
that return a Promise
.
Collection.countDocuments
Summary:
Gets the number of documents matching the filter. For a fast count of the total documents in a collection see estimatedDocumentCount
.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
selector | MongoSelector | A query describing the documents to count | No |
options | Object | All options are listed in MongoDB documentation. Please note that not all of them are available on the client. | No |
// Collection is an instance of Mongo.Collection
/** @returns Promise<number> */
const result = Collection.countDocuments(
MongoSelector, // this param is optional
options, // this param is optional
);
Similar to cursor.count
, but returns a Promise
. For a faster version, see estimatedDocumentCount
.
Collection.estimatedDocumentCount
Summary:
Gets an estimate of the count of documents in a collection using collection metadata. For an exact count of the documents in a collection see countDocuments
.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
options | Object | All options are listed in MongoDB documentation. Please note that not all of them are available on the client. | No |
// Collection is an instance of Mongo.Collection
/** @returns Promise<number> */
const result = Collection.estimatedDocumentCount(
options
);
Returns a Promise
that resolves to the number of documents in the cursor's result set. The count is an estimate and not guaranteed to be exact.
Collection.insert
Summary:
Insert a document in the collection. Returns a promise that will return the document's unique _id when solved.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
doc | Object | The document to insert. May not yet have an _id attribute, in which case Meteor will generate one for you. | Yes |
// Collection is an instance of Mongo.Collection
Collection.insert(
doc
);
WARNING
Client only. For server/isomorphic usage see insertAsync.
Add a document to the collection. A document is just an object, and its fields can contain any combination of EJSON-compatible datatypes (arrays, objects, numbers, strings, null
, true, and false).
insert
will generate a unique ID for the object you pass, insert it in the database, and return the ID. When insert
is called from untrusted client code, it will be allowed only if passes any applicable allow
and deny
rules.
On the server, it should be used insertAsync
that will return a promise with the ID
of your object.
On the client, insert
never blocks. If you do not provide a callback and the insert fails on the server, then Meteor will log a warning to the console. If you provide a callback, Meteor will call that function with error
and result
arguments. In an error case, result
is undefined. If the insert is successful, error
is undefined and result
is the new document ID.
Example:
const groceriesId = Lists.insert({ name: "Groceries" });
Items.insert({ list: groceriesId, name: "Watercress" });
Items.insert({ list: groceriesId, name: "Persimmons" });
Collection.insertAsync
Summary:
Insert a document in the collection. Returns its unique _id.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
doc | Object | The document to insert. May not yet have an _id attribute, in which case Meteor will generate one for you. | Yes |
// Collection is an instance of Mongo.Collection
/** @returns Promise */
const result = Collection.insertAsync(
doc
);
Async version of insert
that return a Promise
.
Collection.update
Summary:
Asynchronously modifies one or more documents in the collection. Returns the number of matched documents.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
selector | MongoSelector | Specifies which documents to modify | Yes |
modifier | MongoModifier | Specifies how to modify the documents | Yes |
options | Object | No | |
callback | function | Optional. If present, called with an error object as the first argument and, if no error, the number of affected documents as the second. | No |
// Collection is an instance of Mongo.Collection
Collection.update(
MongoSelector,
MongoModifier,
options, // this param is optional
() => {}, // this param is optional
);
WARNING
Client only. For server/isomorphic usage see updateAsync.
Modify documents that match selector
according to modifier
(see modifier documentation).
The behavior of update
differs depending on whether it is called by trusted or untrusted code. Trusted code includes server code and method code. Untrusted code includes client-side code such as event handlers and a browser's JavaScript console.
Trusted code can modify multiple documents at once by setting
multi
to true, and can use an arbitrary Mongo selector to find the documents to modify. It bypasses any access control rules set up byallow
anddeny
. The number of affected documents will be returned from theupdate
call if you don't pass a callback.Untrusted code can only modify a single document at once, specified by its
_id
. The modification is allowed only after checking any applicableallow
anddeny
rules. The number of affected documents will be returned to the callback. Untrusted code cannot perform upserts, except in insecure mode.
On the server, it should be used updateAsync
.
On the client, update
never blocks. If you do not provide a callback and the update fails on the server, then Meteor will log a warning to the console. If you provide a callback, Meteor will call that function with an error argument if there was an error, or a second argument indicating the number of affected documents if the update was successful.
// Give the 'Winner' badge to each user with a score greater than 10. If they
// are logged in and their badge list is visible on the screen, it will update
// automatically as they watch.
Meteor.methods({
async declareWinners() {
await Players.updateAsync(
{ score: { $gt: 10 } },
{
$addToSet: { badges: "Winner" },
},
{ multi: true }
);
},
});
// When the 'give points' button in the admin dashboard is pressed, give 5
// points to the current player. The new score will be immediately visible on
// everyone's screens.
Template.adminDashboard.events({
"click .give-points"() {
Players.update(Session.get("currentPlayer"), {
$inc: { score: 5 },
});
},
});
You can use update
to perform a Mongo upsert by setting the upsert
option to true. You can also use the upsert
method to perform an upsert that returns the _id
of the document that was inserted (if there was one) in addition to the number of affected documents.
Collection.updateAsync
Summary:
Modify one or more documents in the collection. Returns the number of matched documents.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
selector | MongoSelector | Specifies which documents to modify | Yes |
modifier | MongoModifier | Specifies how to modify the documents | Yes |
options | Object | No |
// Collection is an instance of Mongo.Collection
/** @returns Promise */
const result = Collection.updateAsync(
MongoSelector,
MongoModifier,
options, // this param is optional
);
Async version of update
that return a Promise
.
Collection.upsert
Summary:
Asynchronously modifies one or more documents in the collection, or insert one if no matching documents were found. Returns an object with keys numberAffected
(the number of documents modified) and insertedId
(the unique _id of the document that was inserted, if any).
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
selector | MongoSelector | Specifies which documents to modify | Yes |
modifier | MongoModifier | Specifies how to modify the documents | Yes |
options | Object | No | |
callback | function | Optional. If present, called with an error object as the first argument and, if no error, the number of affected documents as the second. | No |
// Collection is an instance of Mongo.Collection
Collection.upsert(
MongoSelector,
MongoModifier,
options, // this param is optional
() => {}, // this param is optional
);
WARNING
Client only. For server/isomorphic usage see upsertAsync.
Modify documents that match selector
according to modifier
, or insert a document if no documents were modified. upsert
is the same as calling update
with the upsert
option set to true, except that the return value of upsert
is an object that contain the keys numberAffected
and insertedId
. (update
returns only the number of affected documents.)
Collection.upsertAsync
Summary:
Modify one or more documents in the collection, or insert one if no matching documents were found. Returns an object with keys numberAffected
(the number of documents modified) and insertedId
(the unique _id of the document that was inserted, if any).
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
selector | MongoSelector | Specifies which documents to modify | Yes |
modifier | MongoModifier | Specifies how to modify the documents | Yes |
options | Object | No |
// Collection is an instance of Mongo.Collection
/** @returns Promise */
const result = Collection.upsertAsync(
MongoSelector,
MongoModifier,
options, // this param is optional
);
Async version of upsert
that return a Promise
.
Collection.remove
Summary:
Remove documents from the collection
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
selector | MongoSelector | Specifies which documents to remove | Yes |
callback | function | Optional. If present, called with an error object as the first argument and, if no error, the number of affected documents as the second. | No |
// Collection is an instance of Mongo.Collection
Collection.remove(
MongoSelector,
() => {}, // this param is optional
);
WARNING
Client only. For server/isomorphic usage see removeAsync.
Find all of the documents that match selector
and delete them from the collection.
The behavior of remove
differs depending on whether it is called by trusted or untrusted code. Trusted code includes server code and method code. Untrusted code includes client-side code such as event handlers and a browser's JavaScript console.
Trusted code can use an arbitrary Mongo selector to find the documents to remove, and can remove more than one document at once by passing a selector that matches multiple documents. It bypasses any access control rules set up by
allow
anddeny
. The number of removed documents will be returned fromremove
if you don't pass a callback.As a safety measure, if
selector
is omitted (or isundefined
), no documents will be removed. Setselector
to{}
if you really want to remove all documents from your collection.Untrusted code can only remove a single document at a time, specified by its
_id
. The document is removed only after checking any applicableallow
anddeny
rules. The number of removed documents will be returned to the callback.
On the server, it should be used removeAsync
.
On the client, remove
never blocks. If you do not provide a callback and the remove fails on the server, then Meteor will log a warning to the console. If you provide a callback, Meteor will call that function with an error argument if there was an error, or a second argument indicating the number of removed documents if the remove was successful.
// When the server starts, clear the log and delete all players with a karma of
// less than -2.
Meteor.startup(async () => {
if (Meteor.isServer) {
await Logs.removeAsync({});
await Players.removeAsync({ karma: { $lt: -2 } });
}
});
// When the 'remove' button is clicked on a chat message, delete that message.
Template.chat.events({
"click .remove"() {
Messages.remove(this._id);
},
});
Collection.removeAsync
Summary:
Remove documents from the collection
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
selector | MongoSelector | Specifies which documents to remove | Yes |
// Collection is an instance of Mongo.Collection
/** @returns Promise */
const result = Collection.removeAsync(
MongoSelector
);
Async version of remove
that return a Promise
.
Collection.createIndex server only
server only
Summary:
Asynchronously creates the specified index on the collection.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
index | Object | A document that contains the field and value pairs where the field is the index key and the value describes the type of index for that field. For an ascending index on a field, specify a value of | Yes |
options | Object | All options are listed in MongoDB documentation | No |
// Collection is an instance of Mongo.Collection
Collection.createIndex(
index,
options, // this param is optional
);
For efficient and performant queries you will sometimes need to define indexes other than the default _id
field. You should add indexes to fields (or combinations of fields) you use to lookup documents in a collection. This is where createIndex
comes into play. It takes in 2 objects. First is the key and index type specification (which field and how they should be indexed) and second are options like the index name. For details on how indexes work read the MongoDB documentation.
Note that indexes only apply to server and MongoDB collection. They are not implemented for Minimongo at this time.
Example defining a simple index on Players collection in Meteor:
Players.createIndex({ userId: 1 }, { name: "user reference on players" });
Sometimes you or a package might change an already established indexes. This might throw an error and prevent a startup. For cases where you can afford to re-build indexes or the change affect too many indexes you can set the reCreateIndexOnOptionMismatch
to true in your settings.json
:
{
"packages": {
"mongo": {
"reCreateIndexOnOptionMismatch": true
}
}
}
You should use this option only when you are dealing with a change across many indexes and it is not feasible to fix them manually and you can afford the re-building of the indexes as this will destroy the old index and create a new one. Use this carefully.
Collection.createIndexAsync server only
server only
Summary:
Asynchronously creates the specified index on the collection.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
index | Object | A document that contains the field and value pairs where the field is the index key and the value describes the type of index for that field. For an ascending index on a field, specify a value of | Yes |
options | Object | All options are listed in MongoDB documentation | No |
// Collection is an instance of Mongo.Collection
Collection.createIndexAsync(
index,
options, // this param is optional
);
Async version of createIndex
that return a Promise
.
Collection.allow Server only
Server only
Summary:
Allow users to write directly to this collection from client code, subject to limitations you define.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
options | Object | Yes |
// Collection is an instance of Mongo.Collection
Collection.allow(
options
);
WARNING
While allow
and deny
make it easy to get started building an app, it's harder than it seems to write secure allow
and deny
rules. We recommend that developers avoid allow
and deny
, and switch directly to custom methods once they are ready to remove insecure
mode from their app. See the Meteor Guide on security for more details.
When a client calls insert
/insertAsync
, update
/updateAsync
, remove
/removeAsync
on a collection, the collection's allow
and deny
callbacks are called on the server to determine if the write should be allowed. If at least one allow
callback allows the write, and no deny
callbacks deny the write, then the write is allowed to proceed.
These checks are run only when a client tries to write to the database directly, for example by calling update
/updateAsync
from inside an event handler. Server code is trusted and isn't subject to allow
and deny
restrictions. That includes methods that are called with Meteor.call
— they are expected to do their own access checking rather than relying on allow
and deny
.
You can call allow
as many times as you like, and each call can include any combination of insert
/insertAsync
, update
/updateAsync
, and remove
/removeAsync
functions. The functions should return true
if they think the operation should be allowed. Otherwise they should return false
, or nothing at all (undefined
). In that case Meteor will continue searching through any other allow
rules on the collection.
The available callbacks are:
Callbacks
insert(userId, doc)
/insertAsync(userId, doc)
- The useruserId
wants to insert the documentdoc
into the collection. Returntrue
if this should be allowed.doc
will contain the_id
field if one was explicitly set by the client, or if there is an activetransform
. You can use this to prevent users from specifying arbitrary_id
fields.update(userId, doc, fieldNames, modifier)
/updateAsync(userId, doc, fieldNames, modifier)
- The useruserId
wants to update a documentdoc
in the database. (doc
is the current version of the document from the database, without the proposed update.) Returntrue
to permit the change.fieldNames
is an array of the (top-level) fields indoc
that the client wants to modify, for example['name', 'score']
.modifier
is the raw Mongo modifier that the client wants to execute; for example,{ $set: { 'name.first': 'Alice' }, $inc: { score: 1 } }
.Only Mongo modifiers are supported (operations like
$set
and$push
). If the user tries to replace the entire document rather than use $-modifiers, the request will be denied without checking theallow
functions.remove(userId, doc)
/removeAsync(userId, doc)
- the useruserId
wants to removedoc
from the database. Returntrue
to permit this.
When calling update
/updateAsync
or remove
/removeAsync
Meteor will by default fetch the entire document doc
from the database. If you have large documents you may wish to fetch only the fields that are actually used by your functions. Accomplish this by setting fetch
to an array of field names to retrieve.
Example:
// Create a collection where users can only modify documents that they own.
// Ownership is tracked by an `owner` field on each document. All documents must
// be owned by the user that created them and ownership can't be changed. Only a
// document's owner is allowed to delete it, and the `locked` attribute can be
// set on a document to prevent its accidental deletion.
const Posts = new Mongo.Collection("posts");
Posts.allow({
insert(userId, doc) {
// The user must be logged in and the document must be owned by the user.
return userId && doc.owner === userId;
},
update(userId, doc, fields, modifier) {
// Can only change your own documents.
return doc.owner === userId;
},
remove(userId, doc) {
// Can only remove your own documents.
return doc.owner === userId;
},
async insertAsync(userId, doc) {
// Any custom async validation is supported
const allowed = await allowInsertAsync(userId, doc);
return userId && allowed;
},
async updateAsync(userId, doc, fields, modifier) {
// Any custom async validation is supported
const allowed = await allowUpdateAsync(userId, doc);
return userId && allowed;
},
async removeAsync(userId, doc) {
// Any custom async validation is supported
const allowed = await allowRemoveAsync(userId, doc);
return userId && allowed;
},
fetch: ["owner"],
});
Posts.deny({
update(userId, doc, fields, modifier) {
// Can't change owners.
return _.contains(fields, "owner");
},
remove(userId, doc) {
// Can't remove locked documents.
return doc.locked;
},
async updateAsync(userId, doc, fields, modifier) {
// Any custom async validation is supported
const denied = await denyUpdateAsync(userId, doc);
return userId && denied;
},
async removeAsync(userId, doc) {
// Any custom async validation is supported
const denied = await denyRemoveAsync(userId, doc);
return userId && denied;
},
fetch: ["locked"], // No need to fetch `owner`
});
If you never set up any allow
rules on a collection then all client writes to the collection will be denied, and it will only be possible to write to the collection from server-side code. In this case you will have to create a method for each possible write that clients are allowed to do. You'll then call these methods with Meteor.call
rather than having the clients call insert
/insertAsync
, update
/updateAsync
, and remove
/removeAsync
directly on the collection.
Meteor also has a special "insecure mode" for quickly prototyping new applications. In insecure mode, if you haven't set up any allow
or deny
rules on a collection, then all users have full write access to the collection. This is the only effect of insecure mode. If you call allow
or deny
at all on a collection, even Posts.allow({})
, then access is checked just like normal on that collection. New Meteor projects start in insecure mode by default. To turn it off just run in your terminal:
meteor remove insecure
Collection.deny Server only
Server only
Summary:
Override allow
rules.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
options | Object | Yes |
// Collection is an instance of Mongo.Collection
Collection.deny(
options
);
WARNING
While allow
and deny
make it easy to get started building an app, it's harder than it seems to write secure allow
and deny
rules. We recommend that developers avoid allow
and deny
, and switch directly to custom methods once they are ready to remove insecure
mode from their app. See the Meteor Guide on security for more details.
This works just like allow
, except it lets you make sure that certain writes are definitely denied, even if there is an allow
rule that says that they should be permitted.
When a client tries to write to a collection, the Meteor server first checks the collection's deny
rules. If none of them return true then it checks the collection's allow
rules. Meteor allows the write only if no deny
rules return true
and at least one allow
rule returns true
.
Collection.rawCollection Server only
Server only
Summary:
Returns the Collection
object corresponding to this collection from the npm mongodb
driver module which is wrapped by Mongo.Collection
.
// Collection is an instance of Mongo.Collection
Collection.rawCollection();
The methods (like update
or insert
) you call on the resulting raw collection return promises and can be used outside of a Fiber.
Collection.rawDatabase Server only
Server only
Summary:
Returns the Db
object corresponding to this collection's database connection from the npm mongodb
driver module which is wrapped by Mongo.Collection
.
// Collection is an instance of Mongo.Collection
Collection.rawDatabase();
Cursors
To create a cursor, use find
. To access the documents in a cursor, use forEach
, map
, fetch
, forEachAsync
, mapAsync
, fetchAsync
or ES2015's iteration protocols.
Cursor.forEach
Summary:
Call callback
once for each matching document, sequentially and
synchronously.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
callback | IterationCallback | Function to call. It will be called with three arguments: the document, a 0-based index, and cursor itself. | Yes |
thisArg | Any | An object which will be the value of | No |
// Cursor is an instance of Mongo.Cursor
Cursor.forEach(
IterationCallback,
any, // this param is optional
);
This interface is compatible with Array.forEach.
When called from a reactive computation, forEach
registers dependencies on the matching documents.
Examples:
// Print the titles of the five top-scoring posts.
const topPosts = Posts.find({}, { sort: { score: -1 }, limit: 5 });
let count = 0;
topPosts.forEach((post) => {
console.log(`Title of post ${count}: ${post.title}`);
count += 1;
});
WARNING
Client only. For server/isomorphic usage see removeAsync.
Cursor.forEachAsync
Summary:
Call callback
once for each matching document, sequentially and
synchronously.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
callback | IterationCallback | Function to call. It will be called with three arguments: the document, a 0-based index, and cursor itself. | Yes |
thisArg | Any | An object which will be the value of | No |
// Cursor is an instance of Mongo.Cursor
/** @returns Promise */
const result = Cursor.forEachAsync(
IterationCallback,
any, // this param is optional
);
Async version of forEach
that return a Promise
.
The same example as from forEach
but using forEachAsync
:
// Print the titles of the five top-scoring posts.
const topPosts = Posts.find({}, { sort: { score: -1 }, limit: 5 });
let count = 0;
await topPosts.forEachAsync((post) => {
console.log(`Title of post ${count}: ${post.title}`);
count += 1;
});
console.log("All done!"); // This will be printed after all the posts are printed.
Cursor.map
Summary:
Map callback over all matching documents. Returns an Array.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
callback | IterationCallback | Function to call. It will be called with three arguments: the document, a 0-based index, and cursor itself. | Yes |
thisArg | Any | An object which will be the value of | No |
// Cursor is an instance of Mongo.Cursor
Cursor.map(
IterationCallback,
any, // this param is optional
);
This interface is compatible with Array.map.
When called from a reactive computation, map
registers dependencies on the matching documents.
On the server, if callback
yields, other calls to callback
may occur while the first call is waiting. If strict sequential execution is necessary, use forEach
instead.
WARNING
Client only. For server/isomorphic usage see mapAsync.
Cursor.mapAsync
Summary:
Map callback over all matching documents. Returns an Array.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
callback | IterationCallback | Function to call. It will be called with three arguments: the document, a 0-based index, and cursor itself. | Yes |
thisArg | Any | An object which will be the value of | No |
// Cursor is an instance of Mongo.Cursor
/** @returns Promise */
const result = Cursor.mapAsync(
IterationCallback,
any, // this param is optional
);
Async version of map
that return a Promise
.
Cursor.fetch
Summary:
Return all matching documents as an Array.
// Cursor is an instance of Mongo.Cursor
/** @returns Array<Object> */
const result = Cursor.fetch();
When called from a reactive computation, fetch
registers dependencies on the matching documents.
WARNING
Client only. For server/isomorphic usage see fetchAsync.
Cursor.fetchAsync
Summary:
Return all matching documents as an Array.
// Cursor is an instance of Mongo.Cursor
/** @returns Promise */
const result = Cursor.fetchAsync();
Async version of fetch
that return a Promise
.
Cursor.count
Summary:
Returns the number of documents that match a query. This method is
deprecated since MongoDB 4.0;
see Collection.countDocuments
and
Collection.estimatedDocumentCount
for a replacement.
// Cursor is an instance of Mongo.Cursor
/** @returns Number */
const result = Cursor.count();
Unlike the other functions, count
registers a dependency only on the number of matching documents. (Updates that just change or reorder the documents in the result set will not trigger a recomputation.)
WARNING
Client only. For server/isomorphic usage see countAsync.
Cursor.countAsync
Summary:
Returns the number of documents that match a query. This method is
deprecated since MongoDB 4.0;
see Collection.countDocuments
and
Collection.estimatedDocumentCount
for a replacement.
// Cursor is an instance of Mongo.Cursor
/** @returns Promise */
const result = Cursor.countAsync();
Async version of count
that return a Promise
.
Cursor.observeAsync
Summary:
Watch a query. Receive callbacks as the result set changes.
// Cursor is an instance of Mongo.Cursor
Cursor.observeAsync();
Establishes a live query that invokes callbacks when the result of the query changes. The callbacks receive the entire contents of the document that was affected, as well as its old contents, if applicable. If you only need to receive the fields that changed, see observeChangesAsync
.
callbacks
may have the following functions as properties:
Callbacks
added(document)
oraddedAt(document, atIndex, before)
A new documentdocument
entered the result set. The new document appears at positionatIndex
. It is immediately before the document whose_id
isbefore
.before
will benull
if the new document is at the end of the results.changed(newDocument, oldDocument)
orchangedAt(newDocument, oldDocument, atIndex)
The contents of a document were previouslyoldDocument
and are nownewDocument
. The position of the changed document isatIndex
.removed(oldDocument)
orremovedAt(oldDocument, atIndex)
The documentoldDocument
is no longer in the result set. It used to be at positionatIndex
.movedTo(document, fromIndex, toIndex, before)
A document changed its position in the result set, fromfromIndex
totoIndex
(which is before the document with idbefore
). Its current contents isdocument
.
Use added
, changed
, and removed
when you don't care about the order of the documents in the result set. They are more efficient than addedAt
, changedAt
, and removedAt
.
Before observeAsync
returns, added
(or addedAt
) will be called zero or more times to deliver the initial results of the query.
observeAsync
returns a promise of the live query handle, which is an object with a stop
method. Call stop
with no arguments to stop calling the callback functions and tear down the query. The query will run forever until you call this. If observeAsync
is called from a Tracker.autorun
computation, it is automatically stopped when the computation is rerun or stopped.
TIP
observeAsync
is recommended to keep code isomorphism in the client and server.
observe
stays sync for easier client-side handler management.
(If the cursor was created with the option reactive
set to false, it will only deliver the initial results and will not call any further callbacks; it is not necessary to call stop
on the handle.)
Cursor.observeChangesAsync
Summary:
Watch a query. Receive callbacks as the result set changes. Only the differences between the old and new documents are passed to the callbacks.
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
callbacks | Object | Functions to call to deliver the result set as it changes | Yes |
// Cursor is an instance of Mongo.Cursor
Cursor.observeChangesAsync(
callbacks
);
Establishes a live query that invokes callbacks when the result of the query changes. In contrast to observeAsync
, observeChangesAsync
provides only the difference between the old and new result set, not the entire contents of the document that changed.
callbacks
may have the following functions as properties:
Callbacks
added(id, fields)
oraddedBefore(id, fields, before)
A new document entered the result set. It has theid
andfields
specified.fields
contains all fields of the document excluding the_id
field. The new document is before the document identified bybefore
, or at the end ifbefore
isnull
.changed(id, fields)
The document identified byid
changed its contents.fields
contains the changed fields with their new values. If a field was removed from the document then it will be present infields
with a value ofundefined
.removed(id)
The document identified byid
is no longer in the result set.movedBefore(id, before)
The document identified byid
changed its position in the result set, and now appears before the document identified bybefore
.
observeChangesAsync
is significantly more efficient if you do not use addedBefore
or movedBefore
.
Before observeChangesAsync
returns, added
(or addedBefore
) will be called zero or more times to deliver the initial results of the query.
observeChangesAsync
returns a promise of the live query handle, which is an object with a stop
method. Call stop
with no arguments to stop calling the callback functions and tear down the query. The query will run forever until you call this. If observeChangesAsync
is called from a Tracker.autorun
computation, it is automatically stopped when the computation is rerun or stopped.
TIP
observeChangesAsync
is recommended to keep code isomorphism in the client and server.
observeChanges
stays sync for easier client-side handler management.
(If the cursor was created with the option reactive
set to false, it will only deliver the initial results and will not call any further callbacks; it is not necessary to call stop
on the handle.)
Unlike
observeAsync
,observeChangesAsync
does not provide absolute position information (that is,atIndex
positions rather thanbefore
positions.) This is for efficiency.
Example:
// Keep track of how many administrators are online.
let count = 0;
const cursor = Users.find({ admin: true, onlineNow: true });
const handle = await cursor.observeChangesAsync({
added(id, user) {
count += 1;
console.log(`${user.name} brings the total to ${count} admins.`);
},
removed() {
count -= 1;
console.log(`Lost one. We're now down to ${count} admins.`);
},
});
// After five seconds, stop keeping the count.
setTimeout(() => handle.stop(), 5000);
Mongo.ObjectID
Summary:
Create a Mongo-style ObjectID
. If you don't specify a hexString
, the ObjectID
will be generated randomly (not using MongoDB's ID construction rules).
Arguments:
Source codeName | Type | Description | Required |
---|---|---|---|
hexString | String | Optional. The 24-character hexadecimal contents of the ObjectID to create | No |
import { Mongo } from "meteor/mongo"";
const objectID = new Mongo.ObjectID(
"hexString"
);
Mongo.ObjectID
follows the same API as the Node MongoDB driver ObjectID
class. Note that you must use the equals
method (or EJSON.equals
) to compare them; the ===
operator will not work. If you are writing generic code that needs to deal with _id
fields that may be either strings or ObjectID
s, use EJSON.equals
instead of ===
to compare them.
ObjectID
values created by Meteor will not have meaningful answers to theirgetTimestamp
method, since Meteor currently constructs them fully randomly.
Selectors
The simplest selectors are just a string or Mongo.ObjectID
. These selectors match the document with that value in its _id
field.
A slightly more complex form of selector is an object containing a set of keys that must match in a document:
// Matches all documents where `deleted` is false.
{ deleted: false }
// Matches all documents where the `name` and `cognomen` are as given.
{ name: 'Rhialto', cognomen: 'the Marvelous' }
// Matches every document.
{}
But they can also contain more complicated tests:
// Matches documents where `age` is greater than 18.
{
age: {
$gt: 18;
}
}
// Matches documents where `tags` is an array containing 'popular'.
{
tags: "popular";
}
// Matches documents where `fruit` is one of three possibilities.
{
fruit: {
$in: ["peach", "plum", "pear"];
}
}
See the complete documentation.
Modifiers
A modifier is an object that describes how to update a document in place by changing some of its fields. Some examples:
// Set the `admin` property on the document to true.
{ $set: { admin: true } }
// Add 2 to the `votes` property and add 'Traz' to the end of the `supporters`
// array.
{ $inc: { votes: 2 }, $push: { supporters: 'Traz' } }
But if a modifier doesn't contain any $-operators, then it is instead interpreted as a literal document, and completely replaces whatever was previously in the database. (Literal document modifiers are not currently supported by validated updates.)
// Find the document with ID '123' and completely replace it.
Users.update({ _id: "123" }, { name: "Alice", friends: ["Bob"] });
See the full list of modifiers.
Sort specifiers
Sorts may be specified using your choice of several syntaxes:
// All of these do the same thing (sort in ascending order by key `a`, breaking
// ties in descending order of key `b`).
[['a', 'asc'], ['b', 'desc']]
['a', ['b', 'desc']]
{ a: 1, b: -1 }
// Sorted by `createdAt` descending.
Users.find({}, { sort: { createdAt: -1 } });
// Sorted by `createdAt` descending and by `name` ascending.
Users.find({}, { sort: [['createdAt', 'desc'], ['name', 'asc']] });
The last form will only work if your JavaScript implementation preserves the order of keys in objects. Most do, most of the time, but it's up to you to be sure.
For local collections you can pass a comparator function which receives two document objects, and returns -1 if the first document comes first in order, 1 if the second document comes first, or 0 if neither document comes before the other. This is a Minimongo extension to MongoDB.
Field specifiers
Queries can specify a particular set of fields to include or exclude from the result object.
To exclude specific fields from the result objects, the field specifier is a dictionary whose keys are field names and whose values are 0
. All unspecified fields are included.
Users.find({}, { fields: { password: 0, hash: 0 } });
To include only specific fields in the result documents, use 1
as the value. The _id
field is still included in the result.
Users.find({}, { fields: { firstname: 1, lastname: 1 } });
With one exception, it is not possible to mix inclusion and exclusion styles: the keys must either be all 1 or all 0. The exception is that you may specify _id: 0
in an inclusion specifier, which will leave _id
out of the result object as well. However, such field specifiers can not be used with observeChangesAsync
, observeAsync
, cursors returned from a publish function. They may be used with fetch
, findOne
, forEach
, and map
.
Field operators such as $
and $elemMatch
are not available on the client side yet.
A more advanced example:
Users.insert({
alterEgos: [
{ name: "Kira", alliance: "murderer" },
{ name: "L", alliance: "police" },
],
name: "Yagami Light",
});
Users.findOne({}, { fields: { "alterEgos.name": 1, _id: 0 } });
// Returns { alterEgos: [{ name: 'Kira' }, { name: 'L' }] }
See the MongoDB docs for details of the nested field rules and array behavior.
Connecting to your database
When developing your application, Meteor starts a local MongoDB instance and automatically connects to it. In production, you must specify a MONGO_URL
environment variable pointing at your database in the standard mongo connection string format.
You can also set
MONGO_URL
in development if you want to connect to a different MongoDB instance.
If you want to use oplog tailing for livequeries, you should also set MONGO_OPLOG_URL
(generally you'll need a special user with oplog access, but the detail can differ depending on how you host your MongoDB. Read more here).
As of Meteor 1.4, you must ensure you set the
replicaSet
parameter on yourMETEOR_OPLOG_URL
MongoDB connection options
MongoDB provides many connection options, usually the default works but in some cases you may want to pass additional options. You can do it in two ways:
Meteor settings
You can use your Meteor settings file to set the options in a property called options
inside packages
> mongo
, these values will be provided as options for MongoDB in the connect method.
this option was introduced in Meteor 1.10.2
For example, you may want to specify a certificate for your TLS connection (see the options here) then you could use these options:
"packages": {
"mongo": {
"options": {
"tls": true,
"tlsCAFileAsset": "certificate.pem"
}
}
}
Meteor will convert relative paths to absolute paths if the option name (key) ends with Asset
, for this to work properly you need to place the files in the private
folder in the root of your project. In the example Mongo connection would receive this:
"packages": {
"mongo": {
"options": {
"tls": true,
"tlsCAFile": "/absolute/path/certificate.pem"
}
}
}
See that the final option name (key) does not contain Asset
in the end as expected by MongoDB.
This configuration is necessary in some MongoDB host providers to avoid this error MongoNetworkError: failed to connect to server [sg-meteorappdb-32194.servers.mongodirector.com:27017] on first connect [Error: self signed certificate
.
Another way to avoid this error is to allow invalid certificates with this option:
"packages": {
"mongo": {
"options": {
"tlsAllowInvalidCertificates": true
}
}
}
You can pass any MongoDB valid option, these are just examples using certificates configurations.
If you're using a certificate and having authentication errors when trying to connect to a database other than admin
, make sure to provide the flags &ssl=true&authSource=admin
. You MONGO_URL string should look like this:
mongodb://<username>:<password>@[server-1],[server-2],[server-3]/my-database?replicaSet=my-replica&ssl=true&authSource=admin
Mongo Oplog Options
Oplog options were introduced in Meteor 2.15.1 If you set the
MONGO_OPLOG_URL
env var, Meteor will use MongoDB's Oplog to show efficient, real time updates to your users via your subscriptions.
Due to how Meteor's Oplog implementation is built behind the scenes, if you have certain collections where you expect big amounts of write operations, this might lead to big CPU spikes on your meteor app server, even if you have no publications/subscriptions on any data/documents of these collections. For more information on this, please have a look into this blog post from 2016, this github discussion from 2022 or this meteor forums post from 2023.
To solve this, 2 Oplog settings have been introduced to tweak, which collections are watched or ignored in the oplog.
Exclusion: To exclude for example all updates/inserts of documents in the 2 collections called products
and prices
, you would need to set the following setting in your Meteor settings file:
"packages": {
"mongo": {
"oplogExcludeCollections": ["products", "prices"]
}
}
Inclusion: vice versa, if you only want to watch/include the oplog for changes on documents in the 2 collections chats
and messages
, you would use:
"packages": {
"mongo": {
"oplogIncludeCollections": ["chats", "messages"]
}
}
For obvious reasons, using both oplogExcludeCollections
and oplogIncludeCollections
at the same time is not possible and will result in an error.
Mongo.setConnectionOptions(options)
You can also call Mongo.setConnectionOptions
to set the connection options but you need to call it before any other package using Mongo connections is initialized so you need to add this code in a package and add it above the other packages, like accounts-base in your .meteor/packages
file.
this option was introduced in Meteor 1.4