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DOCS-484 clarify query construction when operating on same field #236

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14 changes: 10 additions & 4 deletions source/reference/operator/and.txt
Original file line number Diff line number Diff line change
Expand Up @@ -39,15 +39,21 @@ $and

db.inventory.find( { price: 1.99, qty: { $lt: 20 } , sale: true } )

If, however, a query requires an ``AND`` operation on the same
field, you *must* use the :operator:`$and` operator as in the
following example:
If, however, a query requires an ``AND`` operation on the same field
such as ``{ $price: { $ne: 1.99 } } AND { price: { $exists: true }
}``, then either use the :operator:`$and` operator for the two
separate expressions or combine the operator expressions for the
field ``{ $price: { $ne: 1.99, $exists: true } }``.

Consider the following examples:

.. code-block:: javascript

db.inventory.update( { $and: [ { price: { $ne: 1.99 } }, { price: { $exists: true } } ] }, { $set: { qty: 15 } } )

This :method:`update() <db.collection.update()>` operation will set
db.inventory.update( { price: { $ne: 1.99, $exists: true } } , { $set: { qty: 15 } } )

Both :method:`update() <db.collection.update()>` operations will set
the value of the ``qty`` field in documents where:

- the ``price`` field value does not equal ``1.99`` **and**
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6 changes: 1 addition & 5 deletions source/reference/operator/exists.txt
Original file line number Diff line number Diff line change
Expand Up @@ -17,15 +17,11 @@ $exists

.. code-block:: javascript

db.inventory.find( { $and: [ { qty: { $exists: true } }, { qty: { $nin: [ 5, 15 ] } } ] } )
db.inventory.find( { qty: { $exists: true, $nin: [ 5, 15 ] } } )

This query will select all documents in the ``inventory`` collection
where the ``qty`` field exists *and* its value does not equal either
``5`` nor ``15``.

The above query used the :operator:`$and` operator because the query
performs an ``AND`` operation on the value of the same field and is
not specific to the :operator:`$exists` operator.

.. seealso::

Expand Down