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- $or (aggregation)
$or (aggregation)¶
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Definition¶
- $or¶
Evaluates one or more expressions and returns true if any of the expressions are true. Otherwise, $or returns false.
$or has the following syntax:
{ $or: [ <expression1>, <expression2>, ... ] }
For more information on expressions, see Expressions.
Behavior¶
$or uses short-circuit logic: the operation stops evaluation after encountering the first true expression.
In addition to the false boolean value, $or evaluates as false the following: null, 0, and undefined values. The $or evaluates all other values as true, including non-zero numeric values and arrays.
Example | Result | |
---|---|---|
{ $or: [ true, false ] } | true | |
{ $or: [ [ false ], false ] } | true | |
{ $or: [ null, 0, undefined ] } | false | |
{ $or: [ ] } | false |
Example¶
Consider an inventory collection with the following documents:
{ "_id" : 1, "item" : "abc1", description: "product 1", qty: 300 }
{ "_id" : 2, "item" : "abc2", description: "product 2", qty: 200 }
{ "_id" : 3, "item" : "xyz1", description: "product 3", qty: 250 }
{ "_id" : 4, "item" : "VWZ1", description: "product 4", qty: 300 }
{ "_id" : 5, "item" : "VWZ2", description: "product 5", qty: 180 }
The following operation uses the $or operator to determine if qty is greater than 250 or less than 200:
db.inventory.aggregate(
[
{
$project:
{
item: 1,
result: { $or: [ { $gt: [ "$qty", 250 ] }, { $lt: [ "$qty", 200 ] } ] }
}
}
]
)
The operation returns the following results:
{ "_id" : 1, "item" : "abc1", "result" : true }
{ "_id" : 2, "item" : "abc2", "result" : false }
{ "_id" : 3, "item" : "xyz1", "result" : false }
{ "_id" : 4, "item" : "VWZ1", "result" : true }
{ "_id" : 5, "item" : "VWZ2", "result" : true }
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