$or¶
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- $or¶
The $or operator performs a logical OR operation on an array of two or more <expressions> and selects the documents that satisfy at least one of the <expressions>. The $or 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¶
在 2.6 版更改.
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¶
在 2.6 版更改.
$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¶
在 2.6 版更改.
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] } } )