$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

The following example uses the movies collection from the sample_mflix sample dataset. For details on how to load this dataset into your deployment, see Load the sample dataset.

This aggregation operation uses the $eq operator to determine if the year field equals 1978:

db.movies.aggregate( [
   { $match: { runtime: { $gt: 1000 } } },
   {
      $project:
        {
          _id: 0,
          title: 1,
          year: 1,
          yearEq1978: { $eq: [ "$year", 1978 ] }
        }
   }
] )

[
  {
    title: 'Centennial',
    year: 1978,
    yearEq1978: true
  },
  {
    title: 'Baseball',
    year: 1994,
    yearEq1978: false
  }
]