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- Match an Array
- Query an Array for an Element
- Specify Multiple Conditions for Array Elements
- Additional Query Tutorials
➤ Use the Select your language drop-down menu in the upper-right to set the language of the following examples.
The following example queries for all documents where the field tags
value is an array with exactly two elements, "red"
and "blank"
, in the specified order:
If, instead, you wish to find an array that contains both the elements "red"
and "blank"
, without regard to order or other elements in the array, use the $all
operator:
The following example queries for all documents where tags
is an array that contains the string "red"
as one of its elements:
For example, the following operation
queries for all documents where the array dim_cm
contains at least one element whose value is greater than 25
.
When specifying compound conditions on array elements, you can specify the query such that either a single array element meets these condition or any combination of array elements meets the conditions.
The following example queries for documents where the dim_cm
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:
Use $elemMatch
operator to specify multiple criteria on the elements of an array such that at least one array element satisfies all the specified criteria.
The
following example queries for documents where the dim_cm
array contains at least one element that is both greater than [$gt
] 22
and less than [$lt
] 30
:
Using dot notation, you can specify query conditions for an element at a particular index or position of the array. The array uses zero-based indexing.
Note
When querying using dot notation, the field and nested field must be inside quotation marks.
The following example queries for all documents where the second element in the
array dim_cm
is greater than 25
:
Use the $size
operator to query for arrays by number of elements. For example, the following selects documents where the array tags
has 3 elements.
For additional query examples, see:
Query Documents
Query on Embedded/Nested Documents
Query an Array of Embedded Documents
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$filter
Selects a subset of an array to return based on the specified condition. Returns an array with only those elements that match the condition. The returned elements are in the original order.
$filter
has the following syntax:
{ $filter: { input: , cond: , as: , limit: } }
| An expression that resolves to an array. |
| An expression that resolves to a boolean value used to determine if an element should be included in the output array. The expression references each element of the |
| Optional. A name for the variable that represents each individual element of the |
| Optional. A number expression that restricts the number of matching array elements that If the specified |
For more information on expressions, see Expressions.
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A collection sales
has the following documents:
db.sales.insertMany[ [ { _id: 0, items: [ { item_id: 43, quantity: 2, price: 10 }, { item_id: 2, quantity: 1, price: 240 } ] }, { _id: 1, items: [ { item_id: 23, quantity: 3, price: 110 }, { item_id: 103, quantity: 4, price: 5 }, { item_id: 38, quantity: 1, price: 300 } ] }, { _id: 2, items: [ { item_id: 4, quantity: 1, price: 23 } ] } ] ]
The following example filters the items
array to only include documents that have a price
greater than or equal to 100
:
db.sales.aggregate[ [ { $project: { items: { $filter: { input: "$items", as: "item", cond: { $gte: [ "$$item.price", 100 ] } } } } } ] ]
The operation produces the following results:
{ "_id" : 0, "items" : [ { "item_id" : 2, "quantity" : 1, "price" : 240 } ] } { "_id" : 1, "items" : [ { "item_id" : 23, "quantity" : 3, "price" : 110 }, { "item_id" : 38, "quantity" : 1, "price" : 300 } ] } { "_id" : 2, "items" : [ ] }
This example uses the sales
collection from the previous example.
The example uses the limit
field to specifiy the number of matching
elements returned in each items
array.
db.sales.aggregate[ [ { $project: { items: { $filter: { input: "$items", cond: { $gte: [ "$$item.price", 100 ] }, as: "item", limit: 1 } } } } ] ]
The operation produces the following results:
{ "_id" : 0, "items" : [ { "item_id" : 2, "quantity" : 1, "price" : 240 } ] } { "_id" : 1, "items" : [ { "item_id" : 23, "quantity" : 3, "price" : 110 } ] } { "_id" : 2, "items" : [ ] }
This example uses the sales
collection from the previous example.
The following example uses a numeric expression for the limit
field to specifiy the number of matching elements returned in each items
array.
db.sales.aggregate[ [ { $project: { items: { $filter: { input: "$items", cond: { $lte: [ "$$item.price", 150] }, as: "item", limit: 2.000 } } } } ] ]
The operation produces the following results:
{ "_id": 0, "items": [ { "item_id": 43, "quantity": 2, "price": 10 } ] }, { "_id": 1, "items": [ { "item_id": 23, "quantity": 3, "price": 110 }, { "item_id": 103, "quantity": 4, "price": 5 } ] }, { "_id": 2, "items": [ { "item_id": 4, "quantity": 1, "price": 23 } ] }
This
example uses the sales
collection from the previous example.
The example uses a limit
field value that is larger than the possible number of matching elements that can be returned.
db.sales.aggregate[ [ { $project: { items: { $filter: { input: "$items", cond: { $gte: [ "$$item.price", 100] }, as: "item", limit: 5 } } } } ] ]
The operation produces the following results:
[ { "_id": 0, "items": [ { "item_id": 2, "quantity": 1, "price": 240 } ] }, { "_id": 1, "items": [ { "item_id": 23, "quantity": 3, "price": 110 }, { "item_id": 38, "quantity": 1, "price": 300 } ] }, { "_id": 2, "items": [] } ]