时间：2021-07-01 10:21:17 帮助过：11人阅读
db.collection.find( <query filter>, <projection> )
For the db.collection.find() method, you can specify the following optional fields:
You can optionally add a cursor modifier to impose limits, skips, and sort orders. The order of documents returned by a query is not defined unless you specify a sort().
The examples on this page use the db.collection.find() method in the mongo shell. In the mongoshell, if the returned cursor is not assigned to a variable using the var keyword, then the cursor is automatically iterated up to 20 times to print up to the first 20 documents in the results.
To populate the users collection referenced in the examples, run the following in mongo shell:
NOTE: If the users collection already contains documents with the same _id values, you need to drop the collection (db.users.drop()) before inserting the example documents.
db.users.insertMany(
[
{
_id: 1,
name: "sue",
age: 19,
type: 1,
status: "P",
favorites: { artist: "Picasso", food: "pizza" },
finished: [ 17, 3 ],
badges: [ "blue", "black" ],
points: [
{ points: 85, bonus: 20 },
{ points: 85, bonus: 10 }
]
},
{
_id: 2,
name: "bob",
age: 42,
type: 1,
status: "A",
favorites: { artist: "Miro", food: "meringue" },
finished: [ 11, 25 ],
badges: [ "green" ],
points: [
{ points: 85, bonus: 20 },
{ points: 64, bonus: 12 }
]
},
{
_id: 3,
name: "ahn",
age: 22,
type: 2,
status: "A",
favorites: { artist: "Cassatt", food: "cake" },
finished: [ 6 ],
badges: [ "blue", "red" ],
points: [
{ points: 81, bonus: 8 },
{ points: 55, bonus: 20 }
]
},
{
_id: 4,
name: "xi",
age: 34,
type: 2,
status: "D",
favorites: { artist: "Chagall", food: "chocolate" },
finished: [ 5, 11 ],
badges: [ "red", "black" ],
points: [
{ points: 53, bonus: 15 },
{ points: 51, bonus: 15 }
]
},
{
_id: 5,
name: "xyz",
age: 23,
type: 2,
status: "D",
favorites: { artist: "Noguchi", food: "nougat" },
finished: [ 14, 6 ],
badges: [ "orange" ],
points: [
{ points: 71, bonus: 20 }
]
},
{
_id: 6,
name: "abc",
age: 43,
type: 1,
status: "A",
favorites: { food: "pizza", artist: "Picasso" },
finished: [ 18, 12 ],
badges: [ "black", "blue" ],
points: [
{ points: 78, bonus: 8 },
{ points: 57, bonus: 7 }
]
}
]
)
View Code
An empty query filter document ({}) selects all documents in the collection:
db.users.find( {} )
Omitting a query filter document to the db.collection.find() is equivalent to specifying an empty query document. As such, the following operation is equivalent to the previous operation:
db.users.find()
A query filter document can specify equality condition with <field>:<value> expressions to select all documents that contain the <field> with the specified <value>:
{ <field1>: <value1>, ... }
The following example retrieves from the users collection all documents where the status field has the value "A":
db.users.find( { status: "A" } )
A query filter document can use the query operators to specify conditions in the following form:
{ <field1>: { <operator1>: <value1> }, ... }
The following example retrieves all documents from the users collection where status equals either "P"or "D":
db.users.find( { status: { $in: [ "P", "D" ] } } )
Although you can express this query using the $or operator, use the $in operator rather than the $or operator when performing equality checks on the same field.
Refer to the Query and Projection Operators document for the complete list of query operators.
A compound query can specify conditions for more than one field in the collection’s documents. Implicitly, a logical AND conjunction connects the clauses of a compound query so that the query selects the documents in the collection that match all the conditions.
The following example retrieves all documents in the users collection where the status equals "A" and age is less than ($lt) 30:
db.users.find( { status: "A", age: { $lt: 30 } } )
See comparison operators for other comparison operators.
Using the $or operator, you can specify a compound query that joins each clause with a logical OR conjunction so that the query selects the documents in the collection that match at least one condition.
The following example retrieves all documents in the collection where the status equals "A" or age is less than ($lt) 30:
db.users.find(
{
$or: [ { status: "A" }, { age: { $lt: 30 } } ]
}
)
NOTE: Queries which use comparison operators are subject to Type Bracketing.
With additional clauses, you can specify precise conditions for matching documents.
In the following example, the compound query document selects all documents in the collection where the``status`` equals "A" and either age is less than than ($lt) 30 or type equals 1:
db.users.find(
{
status: "A",
$or: [ { age: { $lt: 30 } }, { type: 1 } ]
}
)
When the field holds an embedded document, a query can either specify an exact match on the embedded document or specify a match by individual fields in the embedded document using the dot notation.
To specify an exact equality match on the whole embedded document, use the query document { <field>: <value> } where <value> is the document to match. Equality matches on an embedded document require an exact match of the specified <value>, including the field order.
In the following example, the query matches all documents where the favorites field is an embedded document that contains only the fields artist equal to "Picasso" and food equal to "pizza", in that order:
db.users.find( { favorites: { artist: "Picasso", food: "pizza" } } )
Use the dot notation to match by specific fields in an embedded document. Equality matches for specific fields in an embedded document will select documents in the collection where the embedded document contains the specified fields with the specified values. The embedded document can contain additional fields.
In the following example, the query uses the dot notation to match all documents where the favorites field is an embedded document that includes the field artist equal to "Picasso" and may contain other fields:
db.users.find( { "favorites.artist": "Picasso" } )
When the field holds an array, you can query for an exact array match or for specific values in the array. If the array holds embedded documents, you can query for specific fields in the embedded documents using dot notation.
If you specify multiple conditions using the $elemMatch operator, the array must contain at least one element that satisfies all the conditions. See Single Element Satisfies the Criteria.
If you specify multiple conditions without using the $elemMatch operator, then some combination of the array elements, not necessarily a single element, must satisfy all the conditions; i.e. different elements in the array can satisfy different parts of the conditions. See Combination of Elements Satisfies the Criteria.
To specify equality match on an array, use the query document { <field>: <value> } where <value>is the array to match. Equality matches on the array require that the array field match exactly the specified <value>, including the element order.
The following example queries for all documents where the field badges is an array that holds exactly two elements, "blue", and "black", in this order:
db.users.find( { badges: [ "blue", "black" ] } )
The query matches the following document:
{
"_id" : 1,
"name" : "sue",
"age" : 19,
"type" : 1,
"status" : "P",
"favorites" : { "artist" : "Picasso", "food" : "pizza" },
"finished" : [ 17, 3 ]
"badges" : [ "blue", "black" ],
"points" : [ { "points" : 85, "bonus" : 20 }, { "points" : 85, "bonus" : 10 } ]
}
Equality matches can specify a single element in the array to match. These specifications match if the array contains at least one element with the specified value.
The following example queries for all documents where badges is an array that contains "black" as one of its elements:
db.users.find( { badges: "black" } )
The query matches the following documents:
{
"_id" : 1,
"name" : "sue",
"age" : 19,
"type" : 1,
"status" : "P",
"favorites" : { "artist" : "Picasso", "food" : "pizza" },
"finished" : [ 17, 3 ]
"badges" : [ "blue", "black" ],
"points" : [ { "points" : 85, "bonus" : 20 }, { "points" : 85, "bonus" : 10 } ]
}
{
"_id" : 4,
"name" : "xi",
"age" : 34,
"type" : 2,
"status" : "D",
"favorites" : { "artist" : "Chagall", "food" : "chocolate" },
"finished" : [ 5, 11 ],
"badges" : [ "red", "black" ],
"points" : [ { "points" : 53, "bonus" : 15 }, { "points" : 51, "bonus" : 15 } ]
}
{
"_id" : 6,
"name" : "abc",
"age" : 43,
"type" : 1,
"status" : "A",
"favorites" : { "food" : "pizza", "artist" : "Picasso" },
"finished" : [ 18, 12 ],
"badges" : [ "black", "blue" ],
"points" : [ { "points" : 78, "bonus" : 8 }, { "points" : 57, "bonus" : 7 } ]
}
Equality matches can specify equality matches for an element at a particular index or position of the array using the dot notation.
In the following example, the query uses the dot notation to match all documents where the badges is an array that contains "black" as the first element:
db.users.find( { "badges.0": "black" } )
The operation returns the following document:
{
"_id" : 6,
"name" : "abc",
"age" : 43,
"type" : 1,
"status" : "A",
"favorites" : { "food" : "pizza", "artist" : "Picasso" },
"finished" : [ 18, 12 ],
"badges" : [ "black", "blue" ],
"points" : [ { "points" : 78, "bonus" : 8 }, { "points" : 57, "bonus" : 7 } ]
}
Use $elemMatch operator to specify multiple criteria on the elements of an array such that at least one array element satisfies all the specified criteria.
The following example queries for documents where the finished array contains at least one element that is greater than ($gt) 15 and less than ($lt) 20:
db.users.find( { finished: { $elemMatch: { $gt: 15, $lt: 20 } } } )
The operation returns the following documents, whose finished array contains at least one element which meets both criteria:
{
"_id" : 1,
"name" : "sue",
"age" : 19,
"type" : 1,
"status" : "P",
"favorites" : { "artist" : "Picasso", "food" : "pizza" },
"finished" : [ 17, 3 ]
"badges" : [ "blue", "black" ],
"points" : [ { "points" : 85, "bonus" : 20 }, { "points" : 85, "bonus" : 10 } ]
}
{
"_id" : 6,
"name" : "abc",
"age" : 43,
"type" : 1,
"status" : "A",
"favorites" : { "food" : "pizza", "artist" : "Picasso" },
"finished" : [ 18, 12 ],
"badges" : [ "black", "blue" ],
"points" : [ { "points" : 78, "bonus" : 8 }, { "points" : 57, "bonus" : 7 } ]
}
The following example queries for documents where the finished array contains elements that in some combination satisfy the query conditions; e.g., one element can satisfy the greater than 15 condition and another element can satisfy the less than 20 condition, or a single element can satisfy both:
db.users.find( { finished: { $gt: 15, $lt: 20 } } )
The operation returns the following documents:
{
"_id" : 1,
"name" : "sue",
"age" : 19,
"type" : 1,
"status" : "P",
"favorites" : { "artist" : "Picasso", "food" : "pizza" },
"finished" : [ 17, 3 ]
"badges" : [ "blue", "black" ],
"points" : [ { "points" : 85, "bonus" : 20 }, { "points" : 85, "bonus" : 10 } ]
}
{
"_id" : 2,
"name" : "bob",
"age" : 42,
"type" : 1,
"status" : "A",
"favorites" : { "artist" : "Miro", "food" : "meringue" },
"finished" : [ 11, 20 ],
"badges" : [ "green" ],
"points" : [ { "points" : 85, "bonus" : 20 }, { "points" : 64, "bonus" : 12 } ]
}
{
"_id" : 6,
"name" : "abc",
"age" : 43,
"type" : 1,
"status" : "A",
"favorites" : { "food" : "pizza", "artist" : "Picasso" },
"finished" : [ 18, 12 ],
"badges" : [ "black", "blue" ],
"points" : [ { "points" : 78, "bonus" : 8 }, { "points" : 57, "bonus" : 7 } ]
}
If you know the array index of the embedded document, you can specify the document using the embedded document’s position using the dot notation.
The following example selects all documents where the points contains an array whose first element (i.e. index is 0) is a document that contains the field points whose value is less than or equal to 55:
db.users.find( { ‘points.0.points‘: { $lte: 55 } } )
The operation returns the following documents:
{
"_id" : 4,
"name" : "xi",
"age" : 34,
"type" : 2,
"status" : "D",
"favorites" : { "artist" : "Chagall", "food" : "chocolate" },
"finished" : [ 5, 11 ],
"badges" : [ "red", "black" ],
"points" : [ { "points" : 53, "bonus" : 15 }, { "points" : 51, "bonus" : 15 } ]
}
If you do not know the index position of the document in the array, concatenate the name of the field that contains the array, with a dot (.) and the name of the field in the embedded document.
The following example selects all documents where the points is an array with at least one embedded document that contains the field points whose value is less than or equal to 55:
db.users.find( { ‘points.points‘: { $lte: 55 } } )
The operation returns the following documents:
{
"_id" : 3,
"name" : "ahn",
"age" : 22,
"type" : 2,
"status" : "A",
"favorites" : { "artist" : "Cassatt", "food" : "cake" },
"finished" : [ 6 ],
"badges" : [ "blue", "red" ],
"points" : [ { "points" : 81, "bonus" : 8 }, { "points" : 55, "bonus" : 20 } ]
}
{
"_id" : 4,
"name" : "xi",
"age" : 34,
"type" : 2,
"status" : "D",
"favorites" : { "artist" : "Chagall", "food" : "chocolate" },
"finished" : [ 5, 11 ],
"badges" : [ "red", "black" ],
"points" : [ { "points" : 53, "bonus" : 15 }, { "points" : 51, "bonus" : 15 } ]
}
Use $elemMatch operator to specify multiple criteria on an array of embedded documents such that at least one embedded document satisfies all the specified criteria.
The following example queries for documents where the points array has at least one embedded document that contains both the field points less than or equal to 70 and the field bonus equal to 20:
db.users.find( { points: { $elemMatch: { points: { $lte: 70 }, bonus: 20 } } } )
The operation returns the following document:
{
"_id" : 3,
"name" : "ahn",
"age" : 22,
"type" : 2,
"status" : "A",
"favorites" : { "artist" : "Cassatt", "food" : "cake" },
"finished" : [ 6 ],
"badges" : [ "blue", "red" ],
"points" : [ { "points" : 81, "bonus" : 8 }, { "points" : 55, "bonus" : 20 } ]
}
The following example queries for documents where the points array contains elements that in some combination satisfy the query conditions; e.g. one element satisfies the points less than or equal to 70condition and another element satisfies the bonus equal to 20 condition, or a single element satisfies both criteria:
db.users.find( { "points.points": { $lte: 70 }, "points.bonus": 20 } )
The query returns the following documents:
{
"_id" : 2,
"name" : "bob",
"age" : 42,
"type" : 1,
"status" : "A",
"favorites" : { "artist" : "Miro", "food" : "meringue" },
"finished" : [ 11, 20 ],
"badges" : [ "green" ],
"points" : [ { "points" : 85, "bonus" : 20 }, { "points" : 64, "bonus" : 12 } ]
}
{
"_id" : 3,
"name" : "ahn",
"age" : 22,
"type" : 2,
"status" : "A",
"favorites" : { "artist" : "Cassatt", "food" : "cake" },
"finished" : [ 6 ],
"badges" : [ "blue", "red" ],
"points" : [ { "points" : 81, "bonus" : 8 }, { "points" : 55, "bonus" : 20 } ]
}
The following methods can also read documents from a collection:
New in version 3.2.
For reads to replica sets and replica set shards, read concern allows clients to choose a level of isolation for their reads.
For more information, see Read Concern.
MongoDB - MongoDB CRUD Operations, Query Documents
标签：oss selectors single project query sam min each ogr