$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 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 }