$eq (aggregation)
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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 the following syntax:{ $eq: [ <expression1>, <expression2> ] } The arguments can be any valid expression. For more information on expressions, see Expressions.
Example
Consider an inventory
collection with the following documents:
{ "_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 }
The following operation uses the $eq
operator to
determine if qty
equals 250
:
db.inventory.aggregate( [ { $project: { item: 1, qty: 1, qtyEq250: { $eq: [ "$qty", 250 ] }, _id: 0 } } ] )
The operation returns the following results:
{ "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 }