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db.collection.find()![](/zh-cn/docs/v5.3/assets/link.svg)
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Definition![](/zh-cn/docs/v5.3/assets/link.svg)
db.collection.find(query, projection)
Important
mongosh Method
This is a
mongosh
method. This is not the documentation forNode.js
or other programming language specific driver methods.In most cases,
mongosh
methods work the same way as the legacymongo
shell methods. However, some legacy methods are unavailable inmongosh
.For the legacy
mongo
shell documentation, refer to the documentation for the corresponding MongoDB Server release: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.
ParameterTypeDescriptionquery
documentOptional. Specifies selection filter using query operators. To return all documents in a collection, omit this parameter or pass an empty document ({}
).documentOptional. 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.
Returns: A cursor to the documents that match the query
criteria. When thefind()
method "returns documents," the method is actually returning a cursor to the documents.
Behavior![](/zh-cn/docs/v5.3/assets/link.svg)
Projection![](/zh-cn/docs/v5.3/assets/link.svg)
Important
Language Consistency
Starting in MongoDB 4.4, as part of making
find()
and
findAndModify()
projection consistent with
aggregation's $project
stage,
The
find()
andfindAndModify()
projection can accept aggregation expressions and syntax.MongoDB enforces additional restrictions with regards to projections. See Projection Restrictions for details.
The projection
parameter determines which fields are returned in
the matching documents. The projection
parameter takes a document
of the following form:
{ <field1>: <value>, <field2>: <value> ... }
Projection | Description |
---|---|
<field>: <1 or true> | Specifies the inclusion of a field. Non-zero integers are also
treated as true . |
<field>: <0 or false> | Specifies the exclusion of a field. |
"<field>.$": <1 or true> | |
<field>: <array projection> | Using the array projection operators $elemMatch ,
$slice , specifies the array element(s) to include,
thereby excluding those elements that do not meet the
expressions. (Not available for views.) |
<field>: <$meta expression> | Using the $meta operator expression, specifies 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. For example,
In versions 4.2 and earlier, any specification value (with
the exception of the previously unsupported document
value) is treated as either New in version 4.4. |
Embedded Field Specification![](/zh-cn/docs/v5.3/assets/link.svg)
For fields in an embedded documents, you can specify the field using either:
dot notation; e.g.
"field.nestedfield": <value>
nested form; e.g.
{ field: { nestedfield: <value> } }
(Starting in MongoDB 4.4)
_id
Field Projection![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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.
Cursor Handling![](/zh-cn/docs/v5.3/assets/link.svg)
Executing db.collection.find()
in mongosh
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.
Read Concern![](/zh-cn/docs/v5.3/assets/link.svg)
To specify the read concern for
db.collection.find()
, use the cursor.readConcern()
method.
Type Bracketing![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
New in version 4.0.
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![](/zh-cn/docs/v5.3/assets/link.svg)
Starting in MongoDB 3.6, MongoDB drivers and mongosh
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 mongosh
create an implicit session and associate 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![](/zh-cn/docs/v5.3/assets/link.svg)
db.collection.find()
can be used inside multi-document 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, multi-document transaction incurs a greater performance cost over single document writes, and the availability of multi-document 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 multi-document transactions.
For additional transactions usage considerations (such as runtime limit and oplog size limit), see also Production Considerations.
Client Disconnection![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
Query for Equality![](/zh-cn/docs/v5.3/assets/link.svg)
The following operation returns documents in the bios collection where
_id
equals5
:db.bios.find( { _id: 5 } ) The following operation returns documents in the bios collection where the field
last
in thename
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![](/zh-cn/docs/v5.3/assets/link.svg)
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 either5
orObjectId("507c35dd8fada716c89d0013")
:db.bios.find( { _id: { $in: [ 5, ObjectId("507c35dd8fada716c89d0013") ] } } ) The following operation uses the
$gt
operator returns all the documents from thebios
collection wherebirth
is greater thannew 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 wherename.last
field starts with the letterN
(or is"LIKE N%"
)db.bios.find( { "name.last": { $regex: /^N/ } } )
For a list of the query operators, see Query Selectors.
Query for Ranges![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
The following examples query the name
embedded field in the
bios collection.
Query Exact Matches on Embedded Documents![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
Query for an Array Element![](/zh-cn/docs/v5.3/assets/link.svg)
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 fieldcontribs
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 ofcontribs
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![](/zh-cn/docs/v5.3/assets/link.svg)
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 withaward
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 theaward
field equals"Turing Award"
and theyear
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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, e.g.
db.bios.find( { }, { _id: 0, name: { last: 1 }, contribs: { $slice: 2 } } )
Use Aggregation Expression![](/zh-cn/docs/v5.3/assets/link.svg)
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:
Iterate the Returned Cursor![](/zh-cn/docs/v5.3/assets/link.svg)
The find()
method returns a
cursor to the results.
In mongosh
, 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 set the
DBQuery.shellBatchSize
variable to change the number of automatically
iterated documents.
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
mongosh
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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![](/zh-cn/docs/v5.3/assets/link.svg)
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'.