$sort
-
$sort
-
The
$sort
modifier orders the elements of an array during a$push
operation.To use the
$sort
modifier, it must appear with the$each
modifier. You can pass an empty array[]
to the$each
modifier such that only the$sort
modifier has an effect.For
<sort specification>
:- To sort array elements that are not documents, or if the array elements are documents, to sort by the whole documents, specify
1
for ascending or-1
for descending. - If the array elements are documents, to sort by a field in the documents, specify a sort document with the field and the direction, i.e.
{ field: 1 }
or{ field: -1 }
. Do not reference the containing array field in the sort specification (e.g.{ "arrayField.field": 1 }
is incorrect).
- To sort array elements that are not documents, or if the array elements are documents, to sort by the whole documents, specify
Behavior
The $sort
modifier can sort array elements that are not documents. In previous versions, the $sort
modifier required the array elements be documents.
If the array elements are documents, the modifier can sort by either the whole document or by a specific field in the documents. In previous versions, the $sort
modifier can only sort by a specific field in the documents.
Trying to use the $sort
modifier without the $each
modifier results in an error. The $sort
no longer requires the $slice
modifier. For a list of modifiers available for $push
, see Modifiers.
Examples
Sort Array of Documents by a Field in the Documents
A collection students
contains the following document:
The following update appends additional documents to the quizzes
array and then sorts all the elements of the array by the ascending score
field:
Important
The sort document refers directly to the field in the documents and does not reference the containing array field quizzes
; i.e. { score: 1 }
and not { "quizzes.score": 1}
After the update, the array elements are in order of ascending score
field.:
Sort Array Elements That Are Not Documents
A collection students
contains the following document:
The following operation adds two more elements to the scores
array and sorts the elements:
The updated document has the elements of the scores
array in ascending order:
Update Array Using Sort Only
A collection students
contains the following document:
To update the tests
field to sort its elements in descending order, specify the { $sort: -1 }
and specify an empty array []
for the $each
modifier, as in the following:
The result of the operation is to update the scores
field to sort its elements in descending order:
Use $sort
with Other $push
Modifiers
A collection students
has the following document:
The following $push
operation uses:
- the
$each
modifier to add multiple documents to thequizzes
array, - the
$sort
modifier to sort all the elements of the modifiedquizzes
array by thescore
field in descending order, and - the
$slice
modifier to keep only the first three sorted elements of thequizzes
array.
The result of the operation is keep only the three highest scoring quizzes:
The order of the modifiers is immaterial to the order in which the modifiers are processed. See Modifiers for details.