mongoDB : $project (aggregation)

$project operator is used to format document, it takes a document that can specify the inclusion of fields, the suppression of the _id field, the addition of new fields, and the resetting the values of existing fields.

Syntax

{ $project: { <specifications> } }

Syntax	Description
<field>: <1 or true>	Specify the inclusion of a field.
_id: <0 or false>	Specify the suppression of the _id field.
<field>: <expression>	Add a new field or reset the value of an existing field.

> db.products.find()
{ "_id" : 1, "name" : "Nokia X3", "category" : "cellphone", "manufacturer" : "Nokia", "price" : 103 }
{ "_id" : 2, "name" : "Dell Inspiron i3147-3750", "category" : "laptop", "manufacturer" : "DELL", "price" : 359 }
{ "_id" : 3, "name" : "Nokia Lumia 521", "category" : "cellphone", "manufacturer" : "Nokia", "price" : 65 }
{ "_id" : 4, "name" : "Google Nexus 9 tablet", "category" : "tablet", "manufacturer" : "Google", "price" : 194 }
{ "_id" : 5, "name" : "Apple MacBook Air MD711LL/B", "category" : "laptop", "manufacturer" : "Apple", "price" : 854 }
{ "_id" : 6, "name" : "Apple MacBook Air MD760LL/B", "category" : "laptop", "manufacturer" : "Apple", "price" : 859 }
{ "_id" : 7, "name" : "Samsung Galaxy S III", "category" : "cellphone", "manufacturer" : "Samsung", "price" : 199 }
{ "_id" : 8, "name" : "Samsung Galaxy S5, White", "category" : "cellphone", "manufacturer" : "Samsung", "price" : 569 }
{ "_id" : 9, "name" : "Samsung Galaxy S2, White", "category" : "cellphone", "manufacturer" : "Samsung", "price" : 469 }
{ "_id" : 10, "name" : "Google Nexus 10 tablet", "category" : "tablet", "manufacturer" : "Google", "price" : 254 }
{ "_id" : 11, "name" : "Nokia x2", "category" : "cellphone", "manufacturer" : "Nokia", "price" : 93 }
{ "_id" : 12, "name" : "Apple iPhone 4", "category" : "cellphone", "manufacturer" : "Apple", "price" : 121 }
{ "_id" : 13, "name" : "Apple iPhone 5", "category" : "cellphone", "manufacturer" : "Apple", "price" : 409 }
{ "_id" : 14, "name" : "Apple iPhone 6", "category" : "cellphone", "manufacturer" : "Apple", "price" : 695 }
>

>

>

> db.products.aggregate([{"$project" : {"_id" : 0, "maker" :"$manufacturer", "details" : {"category" : {"$toUpper" : "$category"}, "price" : "$price"}}}])
{ "maker" : "Nokia", "details" : { "category" : "CELLPHONE", "price" : 103 } }
{ "maker" : "DELL", "details" : { "category" : "LAPTOP", "price" : 359 } }
{ "maker" : "Nokia", "details" : { "category" : "CELLPHONE", "price" : 65 } }
{ "maker" : "Google", "details" : { "category" : "TABLET", "price" : 194 } }
{ "maker" : "Apple", "details" : { "category" : "LAPTOP", "price" : 854 } }
{ "maker" : "Apple", "details" : { "category" : "LAPTOP", "price" : 859 } }
{ "maker" : "Samsung", "details" : { "category" : "CELLPHONE", "price" : 199 } }
{ "maker" : "Samsung", "details" : { "category" : "CELLPHONE", "price" : 569 } }
{ "maker" : "Samsung", "details" : { "category" : "CELLPHONE", "price" : 469 } }
{ "maker" : "Google", "details" : { "category" : "TABLET", "price" : 254 } }
{ "maker" : "Nokia", "details" : { "category" : "CELLPHONE", "price" : 93 } }
{ "maker" : "Apple", "details" : { "category" : "CELLPHONE", "price" : 121 } }
{ "maker" : "Apple", "details" : { "category" : "CELLPHONE", "price" : 409 } }
{ "maker" : "Apple", "details" : { "category" : "CELLPHONE", "price" : 695 } }

Prevoius                                                 Next                                                 Home