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Logical Query Operators

$and

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  • Behavior
  • Examples
$and

Syntax: { $and: [ { <expression1> }, { <expression2> } , ... , { <expressionN> } ] }

$and performs a logical AND operation on an array of one or more expressions (<expression1>, <expression2>, and so on) and selects the documents that satisfy all the expressions.

Note

MongoDB provides an implicit AND operation when specifying a comma separated list of expressions.

Behavior

To allow the query engine to optimize queries, $and handles errors as follows:

  • If any expression supplied to $and would cause an error when evaluated alone, the $and containing the expression may cause an error but an error is not guaranteed.

  • An expression supplied after the first expression supplied to $and may cause an error even if the first expression evaluates to false.

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 $and, may produce an error if there is any document where $x is 0:

db.example.find( {
   $and: [
      { x: { $ne: 0 } },
      { $expr: { $eq: [ { $divide: [ 1, "$x" ] }, 3 ] } }
   ]
} )

Examples

AND Queries With Multiple Expressions Specifying the Same Field

Consider this query:

db.inventory.find( { $and: [ { price: { $ne: 1.99 } }, { price: { $exists: true } } ] } )

The query selects all documents in the inventory collection where:

  • the price field value is not equal to 1.99 and

  • the price field exists.

The query can be rewritten with an implicit AND operation that combines the operator expressions for the price field:

db.inventory.find( { price: { $ne: 1.99, $exists: true } } )

AND Queries With Multiple Expressions Specifying the Same Operator

Consider this query:

db.inventory.find( {
    $and: [
        { $or: [ { qty: { $lt : 10 } }, { qty : { $gt: 50 } } ] },
        { $or: [ { sale: true }, { price : { $lt : 5 } } ] }
    ]
} )

The query selects all documents where:

  • the qty field value is less than 10 or greater than 50, and

  • the sale field value is equal to true or the price field value is less than 5.

The query cannot use an implicit AND operation because it uses the $or operator more than once.

Tip

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