$or
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$or
The
$or
operator performs a logicalOR
operation on an array of one or more<expressions>
and selects the documents that satisfy at least one of the<expressions>
.
Compatibility
You can use $or
for deployments hosted in the following
environments:
MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud
MongoDB Enterprise: The subscription-based, self-managed version of MongoDB
MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB
Syntax
The $or
operator has the following syntax:
{ $or: [ { <expression1> }, { <expression2> }, ... , { <expressionN> } ] }
Consider the following example:
db.inventory.find( { $or: [ { quantity: { $lt: 20 } }, { price: 10 } ] } )
This query will select all documents in the inventory
collection
where either the quantity
field value is less than 20
or the
price
field value equals 10
.
Behaviors
$or
Clauses and Indexes
When evaluating the clauses in the $or
expression, MongoDB
either performs a collection scan or, if all the clauses are supported
by indexes, MongoDB performs index scans. That is, for MongoDB to use
indexes to evaluate an $or
expression, all the clauses in the
$or
expression must be supported by indexes. Otherwise,
MongoDB will perform a collection scan.
When using indexes with $or
queries, each clause of an
$or
can use its own index. Consider the following query:
db.inventory.find( { $or: [ { quantity: { $lt: 20 } }, { price: 10 } ] } )
To support this query, rather than a compound index, you would create
one index on quantity
and another index on price
:
db.inventory.createIndex( { quantity: 1 } ) db.inventory.createIndex( { price: 1 } )
MongoDB can use all but the geoHaystack
index to support $or
clauses.
$or
and text
Queries
If $or
includes a $text
query, all clauses in the
$or
array must be supported by an index. This is because a
$text
query must use an index, and $or
can only use
indexes if all its clauses are supported by indexes. If the
$text
query cannot use an index, the query will return an
error.
$or
and GeoSpatial Queries
$or
supports geospatial clauses with the following exception
for the near clause (near clause includes $nearSphere
and
$near
). $or
cannot contain a near clause with any
other clause.
$or
and Sort Operations
When executing $or
queries with a sort()
,
MongoDB can use indexes that support the $or
clauses.
$or
versus $in
When using $or
with <expressions>
that are equality checks
for the value of the same field, use the $in
operator instead
of the $or
operator.
For example, to select all documents in the inventory
collection
where the quantity
field value equals either 20
or 50
, use the
$in
operator:
db.inventory.find ( { quantity: { $in: [20, 50] } } )
Nested $or
Clauses
You may nest $or
operations.
Error Handling
To allow the query engine to optimize queries, $or
handles
errors as follows:
If any expression supplied to
$or
would cause an error when evaluated alone, the$or
containing the expression may cause an error but an error is not guaranteed.An expression supplied after the first expression supplied to
$or
may cause an error even if the first expression evaluates totrue
.
For example, the following query always produces an error if $x
is
0
:
db.example.find( { $expr: { $eq: [ { $divide: [ 1, "$x" ] }, 3 ] } } )
The following query, which contains multiple expressions supplied to
$or
, may produce an error if there is any document where $x
is 0
:
db.example.find( { $or: [ { x: { $eq: 0 } }, { $expr: { $eq: [ { $divide: [ 1, "$x" ] }, 3 ] } } ] } )