$eq (aggregation)

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Definition

Example

MongoDB 5.0 is end of life as of October 2024. This version of the documentation is no longer supported. To upgrade your 5.0 deployment, see the MongoDB 6.0 upgrade procedures.

Definition

$eq

Compares two values and returns:

true when the values are equivalent.
false when the values are not equivalent.

The $eq compares both value and type, using the specified BSON comparison order for values of different types.

$eq has this syntax:

{ $eq: [ <expression1>, <expression2> ] }

The arguments can be any valid expression. For more information on expressions, see Expressions.

Example

Create an inventory collection with these documents:

db.inventory.insertMany( [
   { _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 }
] )

Use the $eq operator to determine if qty equals 250:

db.inventory.aggregate(
   [
     {
       $project:
          {
            item: 1,
            qty: 1,
            qtyEq250: { $eq: [ "$qty", 250 ] },
            _id: 0
          }
     }
   ]
)

Output:

{ item : "abc1", qty : 300, qtyEq250 : false }
{ item : "abc2", qty : 200, qtyEq250 : false }
{ item : "xyz1", qty : 250, qtyEq250 : true }
{ item : "VWZ1", qty : 300, qtyEq250 : false }
{ item : "VWZ2", qty : 180, qtyEq250 : false }

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$documentNumber

$exp