$or¶
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$or¶ The
$oroperator performs a logicalORoperation on an array of two or more<expressions>and selects the documents that satisfy at least one of the<expressions>. The$orhas 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
inventorycollection where either thequantityfield value is less than20or thepricefield value equals10.
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¶
Changed in version 2.6.
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¶
Changed in version 2.6.
$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¶
Changed in version 2.6.
When executing $or queries with a sort(),
MongoDB can now use indexes that support the $or clauses.
Previous versions did not use the indexes.
$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] } } )