$unset (aggregation)
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Definition
Note
Disambiguation
Syntax
The $unset
stage has the following syntax:
Considerations
$unset
and $project
The $unset
is an alias for the $project
stage that removes/excludes fields:
{ $project: { "<field1>": 0, "<field2>": 0, ... } }
Embedded Fields
To remove/exclude a field or fields within an embedded document, you can use the dot notation, as in:
{ $unset: "<field.nestedfield>" }
or
{ $unset: [ "<field1.nestedfield>", ...] }
Examples
Create a sample books
collection with the following documents:
db.books.insertMany([ { "_id" : 1, title: "Antelope Antics", isbn: "0001122223334", author: { last:"An", first: "Auntie" }, copies: [ { warehouse: "A", qty: 5 }, { warehouse: "B", qty: 15 } ] }, { "_id" : 2, title: "Bees Babble", isbn: "999999999333", author: { last:"Bumble", first: "Bee" }, copies: [ { warehouse: "A", qty: 2 }, { warehouse: "B", qty: 5 } ] } ])
Remove a Single Field
The following example removes the top-level field copies
:
db.books.aggregate([ { $unset: "copies" } ])
Alternatively, you can also use the following syntax:
db.books.aggregate([ { $unset: [ "copies" ] } ])
Either operation returns the following documents:
{ "_id" : 1, "title" : "Antelope Antics", "isbn" : "0001122223334", "author" : { "last" : "An", "first" : "Auntie" } } { "_id" : 2, "title" : "Bees Babble", "isbn" : "999999999333", "author" : { "last" : "Bumble", "first" : "Bee" } }
Remove Top-Level Fields
The following example removes the top-level fields isbn
and
copies
:
db.books.aggregate([ { $unset: [ "isbn", "copies" ] } ])
The $unset
operation outputs the following documents:
{ "_id" : 1, "title" : "Antelope Antics", "author" : { "last" : "An", "first" : "Auntie" } } { "_id" : 2, "title" : "Bees Babble", "author" : { "last" : "Bumble", "first" : "Bee" } }
Remove Embedded Fields
The following example removes the top-level field isbn
, the
embedded field first
(from the name
document) and the embedded field
warehouse
(from the elements in the copies
array):
db.books.aggregate([ { $unset: [ "isbn", "author.first", "copies.warehouse" ] } ])
The $unset
operation outputs the following documents:
{ "_id" : 1, "title" : "Antelope Antics", "author" : { "last" : "An" }, "copies" : [ { "qty" : 5 }, { "qty" : 15 } ] } { "_id" : 2, "title" : "Bees Babble", "author" : { "last" : "Bumble" }, "copies" : [ { "qty" : 2 }, { "qty" : 5 } ] }