$allElementsTrue (aggregation)
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Definition
$allElementsTrue
Evaluates an array as a set and returns
true
if no element in the array isfalse
. Otherwise, returnsfalse
. An empty array returnstrue
.$allElementsTrue
has the following syntax:{ $allElementsTrue: [ <expression> ] } The
<expression>
itself must resolve to an array, separate from the outer array that denotes the argument list. For more information on expressions, see Expressions.
Behavior
If a set contains a nested array element, $allElementsTrue
does not descend
into the nested array but evaluates the array at top-level.
In addition to the false
boolean value, $allElementsTrue
evaluates
as false
the following: null
, 0
, and undefined
values. The $allElementsTrue
evaluates all other values as true
,
including non-zero numeric values and arrays.
Example | Result |
---|---|
{ $allElementsTrue: [ [ true, 1, "someString" ] ] } | true |
{ $allElementsTrue: [ [ [ false ] ] ] } | true |
{ $allElementsTrue: [ [ ] ] } | true |
{ $allElementsTrue: [ [ null, false, 0 ] ] } | false |
Example
Create an example collection named survey
with the following
documents:
db.survey.insertMany([ { "_id" : 1, "responses" : [ true ] }, { "_id" : 2, "responses" : [ true, false ] }, { "_id" : 3, "responses" : [ ] }, { "_id" : 4, "responses" : [ 1, true, "seven" ] }, { "_id" : 5, "responses" : [ 0 ] }, { "_id" : 6, "responses" : [ [ ] ] }, { "_id" : 7, "responses" : [ [ 0 ] ] }, { "_id" : 8, "responses" : [ [ false ] ] }, { "_id" : 9, "responses" : [ null ] }, { "_id" : 10, "responses" : [ undefined ] } ])
The following operation uses the $allElementsTrue
operator to determine if the responses
array only contains values
that evaluate to true
:
db.survey.aggregate( [ { $project: { responses: 1, isAllTrue: { $allElementsTrue: [ "$responses" ] }, _id: 0 } } ] )
The operation returns the following results:
{ "responses" : [ true ], "isAllTrue" : true } { "responses" : [ true, false ], "isAllTrue" : false } { "responses" : [ ], "isAllTrue" : true } { "responses" : [ 1, true, "seven" ], "isAllTrue" : true } { "responses" : [ 0 ], "isAllTrue" : false } { "responses" : [ [ ] ], "isAllTrue" : true } { "responses" : [ [ 0 ] ], "isAllTrue" : true } { "responses" : [ [ false ] ], "isAllTrue" : true } { "responses" : [ null ], "isAllTrue" : false } { "responses" : [ undefined ], "isAllTrue" : false }