Hướng dẫn concat mongodb
Docs Home → MongoDB Manual $concat Concatenates strings and returns the concatenated string.
The arguments can be any valid expression as long as they resolve to strings. For more information on expressions, see Expressions. If the argument resolves to a value of Consider a
The following operation uses the
The operation returns the following results:
Definition¶$concat ¶Concatenates strings and returns the concatenated string.
{ $concat: [ <expression1>, <expression2>, ... ] } The arguments can be any valid expression as long as they resolve to strings. For more information on expressions, see Expressions. If the argument resolves to a value of Examples¶Consider a { "_id" : 1, "item" : "ABC1", quarter: "13Q1", "description" : "product 1" } { "_id" : 2, "item" : "ABC2", quarter: "13Q4", "description" : "product 2" } { "_id" : 3, "item" : "XYZ1", quarter: "14Q2", "description" : null } The following operation uses the db.inventory.aggregate( [ { $project: { itemDescription: { $concat: [ "$item", " - ", "$description" ] } } } ] ) The operation returns the following results: { "_id" : 1, "itemDescription" : "ABC1 - product 1" } { "_id" : 2, "itemDescription" : "ABC2 - product 2" } { "_id" : 3, "itemDescription" : null } |