$eq (expression operator)

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 }