$eq (aggregation)

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 thespecified BSON comparison orderfor values of different types.

$eq has the following syntax:

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

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

Example

Consider an inventory collection with the following documents:

  1. { "_id" : 1, "item" : "abc1", description: "product 1", qty: 300 }
  2. { "_id" : 2, "item" : "abc2", description: "product 2", qty: 200 }
  3. { "_id" : 3, "item" : "xyz1", description: "product 3", qty: 250 }
  4. { "_id" : 4, "item" : "VWZ1", description: "product 4", qty: 300 }
  5. { "_id" : 5, "item" : "VWZ2", description: "product 5", qty: 180 }

The following operation uses the $eq operator todetermine if qty equals 250:

  1. db.inventory.aggregate(
  2.    [
  3.      {
  4.        $project:
  5.           {
  6.             item: 1,
  7.             qty: 1,
  8.             qtyEq250: { $eq: [ "$qty", 250 ] },
  9.             _id: 0
  10.           }
  11.      }
  12.    ]
  13. )

The operation returns the following results:

  1. { "item" : "abc1", "qty" : 300, "qtyEq250" : false }
  2. { "item" : "abc2", "qty" : 200, "qtyEq250" : false }
  3. { "item" : "xyz1", "qty" : 250, "qtyEq250" : true }
  4. { "item" : "VWZ1", "qty" : 300, "qtyEq250" : false }
  5. { "item" : "VWZ2", "qty" : 180, "qtyEq250" : false }