$and¶
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- $and¶
Syntax: { $and: [ { <expression1> }, { <expression2> } , ... , { <expressionN> } ] }
$and performs a logical AND operation on an array of two or more expressions (e.g. <expression1>, <expression2>, etc.) and selects the documents that satisfy all the expressions in the array. The $and operator uses short-circuit evaluation. If the first expression (e.g. <expression1>) evaluates to false, MongoDB will not evaluate the remaining expressions.
注解
MongoDB provides an implicit AND operation when specifying a comma separated list of expressions. Using an explicit AND with the $and operator is necessary when the same field or operator has to be specified in multiple expressions.
Examples¶
AND Queries With Multiple Expressions Specifying the Same Field¶
Consider the following example:
db.inventory.find( { $and: [ { price: { $ne: 1.99 } }, { price: { $exists: true } } ] } )
This query will select all documents in the inventory collection where:
- the price field value is not equal to 1.99 and
- the price field exists.
This query can be also be constructed with an implicit AND operation by combining the operator expressions for the price field. For example, this query can be written as:
db.inventory.find( { price: { $ne: 1.99, $exists: true } } )
AND Queries With Multiple Expressions Specifying the Same Operator¶
Consider the following example:
db.inventory.find( {
$and : [
{ $or : [ { price : 0.99 }, { price : 1.99 } ] },
{ $or : [ { sale : true }, { qty : { $lt : 20 } } ] }
]
} )
This query will return all select all documents where:
- the price field value equals 0.99 or 1.99, and
- the sale field value is equal to true or the qty field value is less than 20.
This query cannot be constructed using an implicit AND operation, because it uses the $or operator more than once.