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Clarify when $elemMatch is not necessary #2058

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Clarify when $elemMatch is not necessary #2058

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22 changes: 20 additions & 2 deletions source/reference/operator/query/elemMatch.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -30,8 +30,8 @@ for :query:`$elemMatch`.
Examples
--------

Element Match
~~~~~~~~~~~~~
Primitive type element match
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Given the following documents in the ``scores`` collection:

Expand Down Expand Up @@ -87,6 +87,24 @@ Specifically, the query matches the following document:

{ "_id" : 3, "results" : [ { "product" : "abc", "score" : 7 }, { "product" : "xyz", "score" : 8 } ] }


Single embedded document field
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you only want to find documents with an array containing one (as
opposed to multiple) embedded document fields that satisfy a condition,
then ``$elemMatch`` is not necessary, and you can just write ``array.field``:

db.survey.find(
{ results: { $elemMatch: { product: "xyz" } } }
)

is equivalent to:

db.survey.find(
{ "results.product": "xyz" } } }
)

For more information on querying arrays, see
:ref:`read-operations-arrays`, including
:ref:`specify-multiple-criteria-for-array-elements` and
Expand Down