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- $eq (aggregation)
$eq (aggregation)¶
- $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 }