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 code

Name	Type	Description	Required
name	String	The name of the collection. If null, creates an unmanaged (unsynchronized) local collection.	Yes
options	Object	undefined	No

Options:

Name	Type	Description	Required
connection	Object	The server connection that will manage this collection. Uses the default connection if not specified. Pass the return value of calling DDP.connect to specify a different server. Pass null to specify no connection. Unmanaged (name is null) collections cannot specify a connection.	No
idGeneration	String	The method of generating the _id fields of new documents in this collection. Possible values: 'STRING': random strings 'MONGO': random Mongo.ObjectID values The default id generation technique is 'STRING'.	No
transform	function	An optional transformation function. Documents will be passed through this function before being returned from fetch or findOneAsync, and before being passed to callbacks of observe, map, forEach, allow, and deny. Transforms are not applied for the callbacks of observeChanges or to cursors returned from publish functions.	No
defineMutationMethods	Boolean	Set to false to skip setting up the mutation methods that enable insert/update/remove from client code. Default true.	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 code

Name	Type	Description	Required
selector	MongoSelector	A query describing the documents to find	No
options	Object	undefined	No

Options:

Name	Type	Description	Required
sort	MongoSortSpecifier	Sort order (default: natural order)	No
skip	Number	Number of results to skip at the beginning	No
limit	Number	Maximum number of results to return	No
fields	MongoFieldSpecifier	Dictionary of fields to return or exclude.	No
reactive	Boolean	(Client only) Default true; pass false to disable reactivity	No
transform	function	Overrides transform on the Collection for this cursor. Pass null to disable transformation.	No
disableOplog	Boolean	(Server only) Pass true to disable oplog-tailing on this query. This affects the way server processes calls to observe on this query. Disabling the oplog can be useful when working with data that updates in large batches.	No
pollingIntervalMs	Number	(Server only) When oplog is disabled (through the use of disableOplog or when otherwise not available), the frequency (in milliseconds) of how often to poll this query when observing on the server. Defaults to 10000ms (10 seconds).	No
pollingThrottleMs	Number	(Server only) When oplog is disabled (through the use of disableOplog or when otherwise not available), the minimum time (in milliseconds) to allow between re-polling when observing on the server. Increasing this will save CPU and mongo load at the expense of slower updates to users. Decreasing this is not recommended. Defaults to 50ms.	No
maxTimeMs	Number	(Server only) If set, instructs MongoDB to set a time limit for this cursor's operations. If the operation reaches the specified time limit (in milliseconds) without the having been completed, an exception will be thrown. Useful to prevent an (accidental or malicious) unoptimized query from causing a full collection scan that would disrupt other database users, at the expense of needing to handle the resulting error.	No
hint	String	(Server only) Overrides MongoDB's default index selection and query optimization process. Specify an index to force its use, either by its name or index specification. You can also specify { $natural : 1 } to force a forwards collection scan, or { $natural : -1 } for a reverse collection scan. Setting this is only recommended for advanced users.	No
readPreference	String	(Server only) Specifies a custom MongoDB readPreference for this particular cursor. Possible values are primary, primaryPreferred, secondary, secondaryPreferred and nearest.	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 code

Name	Type	Description	Required
selector	MongoSelector	A query describing the documents to find	No
options	Object	undefined	No

Options:

Name	Type	Description	Required
sort	MongoSortSpecifier	Sort order (default: natural order)	No
skip	Number	Number of results to skip at the beginning	No
fields	MongoFieldSpecifier	Dictionary of fields to return or exclude.	No
reactive	Boolean	(Client only) Default true; pass false to disable reactivity	No
transform	function	Overrides transform on the Collection for this cursor. Pass null to disable transformation.	No
readPreference	String	(Server only) Specifies a custom MongoDB readPreference for fetching the document. Possible values are primary, primaryPreferred, secondary, secondaryPreferred and nearest.	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 code

Name	Type	Description	Required
selector	MongoSelector	A query describing the documents to find	No
options	Object	undefined	No

Options:

Name	Type	Description	Required
sort	MongoSortSpecifier	Sort order (default: natural order)	No
skip	Number	Number of results to skip at the beginning	No
fields	MongoFieldSpecifier	Dictionary of fields to return or exclude.	No
reactive	Boolean	(Client only) Default true; pass false to disable reactivity	No
transform	function	Overrides transform on the Collection for this cursor. Pass null to disable transformation.	No
readPreference	String	(Server only) Specifies a custom MongoDB readPreference for fetching the document. Possible values are primary, primaryPreferred, secondary, secondaryPreferred and nearest.	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 code

Name	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} */
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 code

Name	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} */
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 code

Name	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

const result = 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 code

Name	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 code

Name	Type	Description	Required
selector	MongoSelector	Specifies which documents to modify	Yes
modifier	MongoModifier	Specifies how to modify the documents	Yes
options	Object	undefined	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

Options:

Name	Type	Description	Required
multi	Boolean	True to modify all matching documents; false to only modify one of the matching documents (the default).	No
upsert	Boolean	True to insert a document if no matching documents are found.	No
arrayFilters	Array	Optional. Used in combination with MongoDB filtered positional operator to specify which elements to modify in an array field.	No

// Collection is an instance of Mongo.Collection

const result = 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 by allow and deny. The number of affected documents will be returned from the update 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 applicable allow and deny 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.

server.js

// 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 }
    );
  },
});

client.js

// 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 code

Name	Type	Description	Required
selector	MongoSelector	Specifies which documents to modify	Yes
modifier	MongoModifier	Specifies how to modify the documents	Yes
options	Object	undefined	No

Options:

Name	Type	Description	Required
multi	Boolean	True to modify all matching documents; false to only modify one of the matching documents (the default).	No
upsert	Boolean	True to insert a document if no matching documents are found.	No
arrayFilters	Array	Optional. Used in combination with MongoDB filtered positional operator to specify which elements to modify in an array field.	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 code

Name	Type	Description	Required
selector	MongoSelector	Specifies which documents to modify	Yes
modifier	MongoModifier	Specifies how to modify the documents	Yes
options	Object	undefined	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

Options:

Name	Type	Description	Required
multi	Boolean	True to modify all matching documents; false to only modify one of the matching documents (the default).	No

// Collection is an instance of Mongo.Collection

const result = 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 code

Name	Type	Description	Required
selector	MongoSelector	Specifies which documents to modify	Yes
modifier	MongoModifier	Specifies how to modify the documents	Yes
options	Object	undefined	No

Options:

Name	Type	Description	Required
multi	Boolean	True to modify all matching documents; false to only modify one of the matching documents (the default).	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 code

Name	Type	Description	Required
selector	MongoSelector	Specifies which documents to remove	Yes

// Collection is an instance of Mongo.Collection

const result = Collection.remove();
  MongoSelector
);

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 and deny. The number of removed documents will be returned from remove if you don't pass a callback.

  As a safety measure, if selector is omitted (or is undefined), no documents will be removed. Set selector 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 applicable allow and deny 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.

server.js

// 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 } });
  }
});

client.js

// 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 code

Name	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

Summary:

Asynchronously creates the specified index on the collection.

Arguments:

Source code

Name	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 1; for descending index, specify a value of -1. Use text for text indexes.	Yes
options	Object	All options are listed in MongoDB documentation	No

Options:

Name	Type	Description	Required
name	String	Name of the index	No
unique	Boolean	Define that the index values must be unique, more at MongoDB documentation	No
sparse	Boolean	Define that the index is sparse, more at MongoDB documentation	No

// Collection is an instance of Mongo.Collection

const result = 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

Summary:

Asynchronously creates the specified index on the collection.

Arguments:

Source code

Name	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 1; for descending index, specify a value of -1. Use text for text indexes.	Yes
options	Object	All options are listed in MongoDB documentation	No

Options:

Name	Type	Description	Required
name	String	Name of the index	No
unique	Boolean	Define that the index values must be unique, more at MongoDB documentation	No
sparse	Boolean	Define that the index is sparse, more at MongoDB documentation	No

// Collection is an instance of Mongo.Collection

const result = Collection.createIndexAsync();
  index,
  options,  // this param is optional 
);

Async version of createIndex that return a Promise.

Collection.allow

Server only

Summary:

Allow users to write directly to this collection from client code, subject to limitations you define.

Arguments:

Source code

Name	Type	Description	Required
options	Object	undefined	Yes

Options:

Name	Type	Description	Required
insertAsync, updateAsync, removeAsync	function	Functions that look at a proposed modification to the database and return true if it should be allowed.	No
fetch	Array.<String>	Optional performance enhancement. Limits the fields that will be fetched from the database for inspection by your update and remove functions.	No
transform	function	Overrides transform on the Collection. Pass null to disable transformation.	No

// Collection is an instance of Mongo.Collection

const result = 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, update, or remove 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 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, update, and remove 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) - The user userId wants to insert the document doc into the collection. Return true if this should be allowed.

  doc will contain the _id field if one was explicitly set by the client, or if there is an active transform. You can use this to prevent users from specifying arbitrary _id fields.

• update(userId, doc, fieldNames, modifier) - The user userId wants to update a document doc in the database. (doc is the current version of the document from the database, without the proposed update.) Return true to permit the change.

  fieldNames is an array of the (top-level) fields in doc 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 the allow functions.

• remove(userId, doc) - the user userId wants to remove doc from the database. Return true to permit this.

When calling update or remove 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;
  },

  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;
  },

  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, update, and remove 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

Summary:

Override allow rules.

Arguments:

Source code

Name	Type	Description	Required
options	Object	undefined	Yes

Options:

Name	Type	Description	Required
insertAsync, updateAsync, removeAsync	function	Functions that look at a proposed modification to the database and return true if it should be denied, even if an allow rule says otherwise.	No
fetch	Array.<String>	Optional performance enhancement. Limits the fields that will be fetched from the database for inspection by your update and remove functions.	No
transform	function	Overrides transform on the Collection. Pass null to disable transformation.	No

// Collection is an instance of Mongo.Collection

const result = 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

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

const result = 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

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

const result = 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 code

Name	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 this inside callback.	No

// Cursor is an instance of Mongo.Cursor

const result = 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 code

Name	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 this inside callback.	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 code

Name	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 this inside callback.	No

// Cursor is an instance of Mongo.Cursor

const result = 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 code

Name	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 this inside callback.	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