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db.collection.find()

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  • Definition
  • Compatibility
  • Syntax
  • Behavior
  • Examples

Definition

db.collection.find(query, projection)

Important

mongo Shell Method

This page documents a mongo method. This is not the documentation for database commands or language-specific drivers, such as Node.js. To use the database command, see the find command.

For MongoDB API drivers, refer to the language-specific MongoDB driver documentation.

Selects documents in a collection or view and returns a cursor to the selected documents.

Returns:A cursor to the documents that match the query criteria. When the find() method "returns documents," the method is actually returning a cursor to the documents.

Compatibility

You can use db.collection.find() for deployments hosted in the following environments:

  • MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud

Syntax

The find() method has the following form:

db.collection.find( <query>, <projection>, <options> )

The find() method takes the following parameters:

Parameter
Type
Description
document

Optional. Specifies selection filter using query operators. To return all documents in a collection, omit this parameter or pass an empty document ({}).

document

Optional. Specifies the fields to return in the documents that match the query filter. To return all fields in the matching documents, omit this parameter. For details, see Projection.

Behavior

Projection

Important

Language Consistency

Starting in MongoDB 4.4, as part of making find() and findAndModify() projection consistent with aggregation's $project stage,

The projection parameter determines which fields are returned in the matching documents. The projection parameter takes a document of the following form:

{ <field1>: <value>, <field2>: <value> ... }
Projection
Description
<field>: <1 or true>
Specifies the inclusion of a field. If you specify a non-zero integer for the projection value, the operation treats the value as true.
<field>: <0 or false>
Specifies the exclusion of a field.
"<field>.$": <1 or true>

Uses the $ array projection operator to return the first element that matches the query condition on the array field. If you specify a non-zero integer for the projection value, the operation treats the value as true.

Not available for views.

<field>: <array projection>

Uses the array projection operators ($elemMatch, $slice) to specify the array elements to include.

Not available for views.

<field>: <$meta expression>

Uses the $meta operator expression to specify the inclusion of available per-document metadata.

Not available for views.

<field>: <aggregation expression>

Specifies the value of the projected field.

Starting in MongoDB 4.4, with the use of aggregation expressions and syntax, including the use of literals and aggregation variables, you can project new fields or project existing fields with new values.

  • If you specify a non-numeric, non-boolean literal (such as a literal string or an array or an operator expression) for the projection value, the field is projected with the new value, for example:

    • { field: [ 1, 2, 3, "$someExistingField" ] }

    • { field: "New String Value" }

    • { field: { status: "Active", total: { $sum: "$existingArray" } } }

  • To project a literal value for a field, use the $literal aggregation expression; for example:

    • { field: { $literal: 5 } }

    • { field: { $literal: true } }

    • { field: { $literal: { fieldWithValue0: 0, fieldWithValue1: 1 } } }

In versions 4.2 and earlier, any specification value (with the exception of the previously unsupported document value) is treated as either true or false to indicate the inclusion or exclusion of the field.

New in version 4.4.

Embedded Field Specification

For fields in an embedded documents, you can specify the field using either:

  • dot notation, for example "field.nestedfield": <value>

  • nested form, for example { field: { nestedfield: <value> } } (Starting in MongoDB 4.4)

_id Field Projection

The _id field is included in the returned documents by default unless you explicitly specify _id: 0 in the projection to suppress the field.

Inclusion or Exclusion

A projection cannot contain both include and exclude specifications, with the exception of the _id field:

  • In projections that explicitly include fields, the _id field is the only field that you can explicitly exclude.

  • In projections that explicitly excludes fields, the _id field is the only field that you can explicitly include; however, the _id field is included by default.

See Projection Examples.

Cursor Handling

Executing db.collection.find() in the mongo shell automatically iterates the cursor to display up to the first 20 documents. Type it to continue iteration.

To access the returned documents with a driver, use the appropriate cursor handling mechanism for the driver language.

Tip

See also:

Read Concern

To specify the read concern for db.collection.find(), use the cursor.readConcern() method.

Type Bracketing

MongoDB treats some data types as equivalent for comparison purposes. For instance, numeric types undergo conversion before comparison. For most data types, however, comparison operators only perform comparisons on documents where the BSON type of the target field matches the type of the query operand. Consider the following collection:

{ "_id": "apples", "qty": 5 }
{ "_id": "bananas", "qty": 7 }
{ "_id": "oranges", "qty": { "in stock": 8, "ordered": 12 } }
{ "_id": "avocados", "qty": "fourteen" }

The following query uses $gt to return documents where the value of qty is greater than 4.

db.collection.find( { qty: { $gt: 4 } } )

The query returns the following documents:

{ "_id": "apples", "qty": 5 }
{ "_id": "bananas", "qty": 7 }

The document with _id equal to "avocados" is not returned because its qty value is of type string while the $gt operand is of type integer.

The document with _id equal to "oranges" is not returned because its qty value is of type object.

Note

To enforce data types in a collection, use Schema Validation.

Sessions

For cursors created inside a session, you cannot call getMore outside the session.

Similarly, for cursors created outside of a session, you cannot call getMore inside a session.

Session Idle Timeout

MongoDB drivers and mongo shell associate all operations with a server session, with the exception of unacknowledged write operations. For operations not explicitly associated with a session (i.e. using Mongo.startSession()), MongoDB drivers and the mongo shell creates an implicit session and associates it with the operation.

If a session is idle for longer than 30 minutes, the MongoDB server marks that session as expired and may close it at any time. When the MongoDB server closes the session, it also kills any in-progress operations and open cursors associated with the session. This includes cursors configured with noCursorTimeout() or a maxTimeMS() greater than 30 minutes.

For operations that may be idle for longer than 30 minutes, associate the operation with an explicit session using Mongo.startSession() and periodically refresh the session using the refreshSessions command. See Session Idle Timeout for more information.

Transactions

db.collection.find() can be used inside distributed transactions.

  • For cursors created outside of a transaction, you cannot call getMore inside the transaction.

  • For cursors created in a transaction, you cannot call getMore outside the transaction.

Important

In most cases, a distributed transaction incurs a greater performance cost over single document writes, and the availability of distributed transactions should not be a replacement for effective schema design. For many scenarios, the denormalized data model (embedded documents and arrays) will continue to be optimal for your data and use cases. That is, for many scenarios, modeling your data appropriately will minimize the need for distributed transactions.

For additional transactions usage considerations (such as runtime limit and oplog size limit), see also Production Considerations.

Client Disconnection

Starting in MongoDB 4.2, if the client that issued db.collection.find() disconnects before the operation completes, MongoDB marks db.collection.find() for termination using killOp.

Examples

The examples in this section use documents from the bios collection where the documents generally have the form:

{
    "_id" : <value>,
    "name" : { "first" : <string>, "last" : <string> },       // embedded document
    "birth" : <ISODate>,
    "death" : <ISODate>,
    "contribs" : [ <string>, ... ],                           // Array of Strings
    "awards" : [
        { "award" : <string>, year: <number>, by: <string> }  // Array of embedded documents
        ...
    ]
}

To create and populate the bios collection, see The bios Example Collection.

Find All Documents in a Collection

The find() method with no parameters returns all documents from a collection and returns all fields for the documents. For example, the following operation returns all documents in the bios collection:

db.bios.find()

Find Documents that Match Query Criteria

Query for Equality

  • The following operation returns documents in the bios collection where _id equals 5:

    db.bios.find( { _id: 5 } )

  • The following operation returns documents in the bios collection where the field last in the name embedded document equals "Hopper":

    db.bios.find( { "name.last": "Hopper" } )

    Note

    To access fields in an embedded document, use dot notation ("<embedded document>.<field>").

Query Using Operators

To find documents that match a set of selection criteria, call find() with the <criteria> parameter.

MongoDB provides various query operators to specify the criteria.

  • The following operation uses the $in operator to return documents in the bios collection where _id equals either 5 or ObjectId("507c35dd8fada716c89d0013"):

    db.bios.find(
       { _id: { $in: [ 5, ObjectId("507c35dd8fada716c89d0013") ] } }
    )

  • The following operation uses the $gt operator returns all the documents from the bios collection where birth is greater than new Date('1950-01-01'):

    db.bios.find( { birth: { $gt: new Date('1950-01-01') } } )

  • The following operation uses the $regex operator to return documents in the bios collection where name.last field starts with the letter N (or is "LIKE N%")

    db.bios.find(
       { "name.last": { $regex: /^N/ } }
    )

For a list of the query operators, see Query Selectors.

Query for Ranges

Combine comparison operators to specify ranges for a field. The following operation returns from the bios collection documents where birth is between new Date('1940-01-01') and new Date('1960-01-01') (exclusive):

db.bios.find( { birth: { $gt: new Date('1940-01-01'), $lt: new Date('1960-01-01') } } )

For a list of the query operators, see Query Selectors.

Query for Multiple Conditions

The following operation returns all the documents from the bios collection where birth field is greater than new Date('1950-01-01') and death field does not exists:

db.bios.find( {
   birth: { $gt: new Date('1920-01-01') },
   death: { $exists: false }
} )

For a list of the query operators, see Query Selectors.

Query Embedded Documents

The following examples query the name embedded field in the bios collection.

Query Exact Matches on Embedded Documents

The following operation returns documents in the bios collection where the embedded document name is exactly { first: "Yukihiro", last: "Matsumoto" }, including the order:

db.bios.find(
    { name: { first: "Yukihiro", last: "Matsumoto" } }
)

The name field must match the embedded document exactly. The query does not match documents with the following name fields:

{
   first: "Yukihiro",
   aka: "Matz",
   last: "Matsumoto"
}
{
   last: "Matsumoto",
   first: "Yukihiro"
}

Query Fields of an Embedded Document

The following operation returns documents in the bios collection where the embedded document name contains a field first with the value "Yukihiro" and a field last with the value "Matsumoto". The query uses dot notation to access fields in an embedded document:

db.bios.find(
   {
     "name.first": "Yukihiro",
     "name.last": "Matsumoto"
   }
)

The query matches the document where the name field contains an embedded document with the field first with the value "Yukihiro" and a field last with the value "Matsumoto". For instance, the query would match documents with name fields that held either of the following values:

{
  first: "Yukihiro",
  aka: "Matz",
  last: "Matsumoto"
}
{
  last: "Matsumoto",
  first: "Yukihiro"
}

For more information and examples, see also Query on Embedded/Nested Documents.

Query Arrays

Query for an Array Element

The following examples query the contribs array in the bios collection.

  • The following operation returns documents in the bios collection where the array field contribs contains the element "UNIX":

    db.bios.find( { contribs: "UNIX" } )

  • The following operation returns documents in the bios collection where the array field contribs contains the element "ALGOL" or "Lisp":

    db.bios.find( { contribs: { $in: [ "ALGOL", "Lisp" ]} } )

  • The following operation use the $all query operator to return documents in the bios collection where the array field contribs contains both the elements "ALGOL" and "Lisp":

    db.bios.find( { contribs: { $all: [ "ALGOL", "Lisp" ] } } )

    For more examples, see $all. See also $elemMatch.

  • The following operation uses the $size operator to return documents in the bios collection where the array size of contribs is 4:

    db.bios.find( { contribs: { $size: 4 } } )

For more information and examples of querying an array, see:

For a list of array specific query operators, see Array.

Query an Array of Documents

The following examples query the awards array in the bios collection.

  • The following operation returns documents in the bios collection where the awards array contains an element with award field equals "Turing Award":

    db.bios.find(
       { "awards.award": "Turing Award" }
    )

  • The following operation returns documents in the bios collection where the awards array contains at least one element with both the award field equals "Turing Award" and the year field greater than 1980:

    db.bios.find(
       { awards: { $elemMatch: { award: "Turing Award", year: { $gt: 1980 } } } }
    )

    Use the $elemMatch operator to specify multiple criteria on an array element.

For more information and examples of querying an array, see:

For a list of array specific query operators, see Array.

Projections

The projection parameter specifies which fields to return. The parameter contains either include or exclude specifications, not both, unless the exclude is for the _id field.

Note

Unless the _id field is explicitly excluded in the projection document _id: 0, the _id field is returned.

Specify the Fields to Return

The following operation finds all documents in the bios collection and returns only the name field, contribs field and _id field:

db.bios.find( { }, { name: 1, contribs: 1 } )

Note

Unless the _id field is explicitly excluded in the projection document _id: 0, the _id field is returned.

Explicitly Excluded Fields

The following operation queries the bios collection and returns all fields except the first field in the name embedded document and the birth field:

db.bios.find(
   { contribs: 'OOP' },
   { 'name.first': 0, birth: 0 }
)

Explicitly Exclude the _id Field

Note

Unless the _id field is explicitly excluded in the projection document _id: 0, the _id field is returned.

The following operation finds documents in the bios collection and returns only the name field and the contribs field:

db.bios.find(
   { },
   { name: 1, contribs: 1, _id: 0 }
)

On Arrays and Embedded Documents

The following operation queries the bios collection and returns the last field in the name embedded document and the first two elements in the contribs array:

db.bios.find(
   { },
   { _id: 0, 'name.last': 1, contribs: { $slice: 2 } } )

Starting in MongoDB 4.4, you can also specify embedded fields using the nested form, for example:

db.bios.find(
   { },
   { _id: 0, name: { last: 1 }, contribs: { $slice: 2 } }
)

Use Aggregation Expression

Starting in MongoDB 4.4, db.collection.find() projection can accept aggregation expressions and syntax.

With the use of aggregation expressions and syntax, you can project new fields or project existing fields with new values. For example, the following operation uses aggregation expressions to override the value of the name and awards fields as well as to include new fields reportDate, reportBy, and reportNumber.

db.bios.find(
   { },
   {
     _id: 0,
     name: {
        $concat: [
           { $ifNull: [ "$name.aka", "$name.first" ] },
           " ",
           "$name.last"
        ]
     },
     birth: 1,
     contribs: 1,
     awards: { $cond: { if: { $isArray: "$awards" }, then: { $size: "$awards" }, else: 0 } },
     reportDate: { $dateToString: {  date: new Date(), format: "%Y-%m-%d" } },
     reportBy: "hellouser123",
     reportNumber: { $literal: 1 }
   }
)

To set the reportRun field to the value 1 The operation returns the following documents:

{ "birth" : ISODate("1924-12-03T05:00:00Z"), "contribs" : [ "Fortran", "ALGOL", "Backus-Naur Form", "FP" ], "name" : "John Backus", "awards" : 4, "reportDate" : "2020-06-05", "reportBy" : "hellouser123", "reportNumber" : 1 }
{ "birth" : ISODate("1927-09-04T04:00:00Z"), "contribs" : [ "Lisp", "Artificial Intelligence", "ALGOL" ], "name" : "John McCarthy", "awards" : 3, "reportDate" : "2020-06-05", "reportBy" : "hellouser123", "reportNumber" : 1 }
{ "birth" : ISODate("1906-12-09T05:00:00Z"), "contribs" : [ "UNIVAC", "compiler", "FLOW-MATIC", "COBOL" ], "name" : "Grace Hopper", "awards" : 4, "reportDate" : "2020-06-05", "reportBy" : "hellouser123", "reportNumber" : 1 }
{ "birth" : ISODate("1926-08-27T04:00:00Z"), "contribs" : [ "OOP", "Simula" ], "name" : "Kristen Nygaard", "awards" : 3, "reportDate" : "2020-06-05", "reportBy" : "hellouser123", "reportNumber" : 1 }
{ "birth" : ISODate("1931-10-12T04:00:00Z"), "contribs" : [ "OOP", "Simula" ], "name" : "Ole-Johan Dahl", "awards" : 3, "reportDate" : "2020-06-05", "reportBy" : "hellouser123", "reportNumber" : 1 }
{ "birth" : ISODate("1956-01-31T05:00:00Z"), "contribs" : [ "Python" ], "name" : "Guido van Rossum", "awards" : 2, "reportDate" : "2020-06-05", "reportBy" : "hellouser123", "reportNumber" : 1 }
{ "birth" : ISODate("1941-09-09T04:00:00Z"), "contribs" : [ "UNIX", "C" ], "name" : "Dennis Ritchie", "awards" : 3, "reportDate" : "2020-06-05", "reportBy" : "hellouser123", "reportNumber" : 1 }
{ "birth" : ISODate("1965-04-14T04:00:00Z"), "contribs" : [ "Ruby" ], "name" : "Matz Matsumoto", "awards" : 1, "reportDate" : "2020-06-05", "reportBy" : "hellouser123", "reportNumber" : 1 }
{ "birth" : ISODate("1955-05-19T04:00:00Z"), "contribs" : [ "Java" ], "name" : "James Gosling", "awards" : 2, "reportDate" : "2020-06-05", "reportBy" : "hellouser123", "reportNumber" : 1 }
{ "contribs" : [ "Scala" ], "name" : "Martin Odersky", "awards" : 0, "reportDate" : "2020-06-05", "reportBy" : "hellouser123", "reportNumber" : 1 }

Tip

See also:

Project Fields to Return from Query

Iterate the Returned Cursor

The find() method returns a cursor to the results.

In the mongo shell, if the returned cursor is not assigned to a variable using the var keyword, the cursor is automatically iterated to access up to the first 20 documents that match the query. You can update the displayBatchSize variable to change the number of automatically iterated documents.

The following example sets the batch size to 3. Future db.collection.find() operations will only return 3 documents per cursor iteration.

config.set( "displayBatchSize", 3 )

To manually iterate over the results, assign the returned cursor to a variable with the var keyword, as shown in the following sections.

With Variable Name

The following example uses the variable myCursor to iterate over the cursor and print the matching documents:

var myCursor = db.bios.find( );
myCursor

With next() Method

The following example uses the cursor method next() to access the documents:

var myCursor = db.bios.find( );
var myDocument = myCursor.hasNext() ? myCursor.next() : null;
if (myDocument) {
    var myName = myDocument.name;
    print (tojson(myName));
}

To print, you can also use the printjson() method instead of print(tojson()):

if (myDocument) {
   var myName = myDocument.name;
   printjson(myName);
}

With forEach() Method

The following example uses the cursor method forEach() to iterate the cursor and access the documents:

var myCursor = db.bios.find( );
myCursor.forEach(printjson);

Modify the Cursor Behavior

The mongo shell and the drivers provide several cursor methods that call on the cursor returned by the find() method to modify its behavior.

Order Documents in the Result Set

The sort() method orders the documents in the result set. The following operation returns documents in the bios collection sorted in ascending order by the name field:

db.bios.find().sort( { name: 1 } )

sort() corresponds to the ORDER BY statement in SQL.

Limit the Number of Documents to Return

The limit() method limits the number of documents in the result set. The following operation returns at most 5 documents in the bios collection:

db.bios.find().limit( 5 )

limit() corresponds to the LIMIT statement in SQL.

Set the Starting Point of the Result Set

The skip() method controls the starting point of the results set. The following operation skips the first 5 documents in the bios collection and returns all remaining documents:

db.bios.find().skip( 5 )

Specify Collation

Collation allows users to specify language-specific rules for string comparison, such as rules for lettercase and accent marks.

The collation() method specifies the collation for the db.collection.find() operation.

db.bios.find( { "name.last": "hopper" } ).collation( { locale: "en_US", strength: 1 } )

Combine Cursor Methods

The following statements chain cursor methods limit() and sort():

db.bios.find().sort( { name: 1 } ).limit( 5 )
db.bios.find().limit( 5 ).sort( { name: 1 } )

The two statements are equivalent; i.e. the order in which you chain the limit() and the sort() methods is not significant. Both statements return the first five documents, as determined by the ascending sort order on 'name'.

Available mongo Shell Cursor Methods

Back

db.collection.explain()

Next

db.collection.findAndModify()