FQL v4 will be decommissioned on June 30, 2025. Ensure that you complete your migration from FQL v4 to FQL v10 by that date.

Fauna accounts created after August 21, 2024 must use FQL v10. These accounts will not be able to run FQL v4 queries or access the v4 Dashboard.

For more details, see the v4 EOL announcement and migration guide. Contact support@fauna.com with any questions.

IsCollection

This reference topic applies to FQL v4. Go to this page for the latest FQL v10 reference topics.

 
IsCollection( value )
is_collection( value )
IsCollection( value )
IsCollection( value )
IsCollection( value )
IsCollection( value )

Description

The IsCollection function returns true only if value is a collection, otherwise it returns false.

Parameters

Parameter Type Definition and Requirements

value

Any

Any value, which is to be tested to determine whether it is a collection or not.

Returns

Returns a Boolean, indicating whether value was a collection or not.

Examples

The following query uses Map to iterate over an array of all of the types of values that can be tested by a type-check function, passing each item into a Lambda function that returns an object, which contains the value and the result of calling IsCollection with that value:

client.query(
  q.Map(
    [
      ['array'],
      true,
      false,
      new Uint8Array([1, 2, 3, 4]),
      [0x1, 0x2, 0x3, 0x4],
      q.Collection('Letters'),
      q.Ref('credentials/self'),
      q.Database('child_db'),
      q.Date('2019-11-12'),
      q.Ref(q.Collection('Letters'), 123),
      10.1,
      q.Function('double'),
      q.Index('letters'),
      10,
      q.Ref(q.Keys(), '1'),
      q.Query(q.Lambda('x', q.Var('x'))),
      null,
      { x: 10 },
      q.Role('employees'),
      q.Match(q.Index('letters')),
      'ten',
      '10',
      q.Time('2020-07-06T12:34:56.789Z'),
      q.Ref(q.Tokens(), '1'),
    ],
    q.Lambda('x', {
      value: q.Var('x'),
      IsCollection: q.IsCollection(q.Var('x')),
    })
  )
)
.then((ret) => console.log(ret))
.catch((err) => console.error(
  'Error: [%s] %s: %s',
  err.name,
  err.message,
  err.errors()[0].description,
))
[
  { value: [ 'array' ], IsCollection: false },
  { value: true, IsCollection: false },
  { value: false, IsCollection: false },
  { value: Bytes("AQIDBA=="), IsCollection: false },
  { value: [ 1, 2, 3, 4 ], IsCollection: false },
  { value: Collection("Letters"), IsCollection: true },
  {
    value: Ref(Credentials(), "268431923988136448"),
    IsCollection: false
  },
  { value: Database("child_db"), IsCollection: false },
  { value: Date("2019-11-12"), IsCollection: false },
  { value: Ref(Collection("Letters"), "123"), IsCollection: false },
  { value: 10.1, IsCollection: false },
  { value: Function("double"), IsCollection: false },
  { value: Index("letters"), IsCollection: false },
  { value: 10, IsCollection: false },
  { value: Ref(Keys(), "1"), IsCollection: false },
  { value: Query(Lambda("x", Var("x"))), IsCollection: false },
  { value: null, IsCollection: false },
  { value: { x: 10 }, IsCollection: false },
  { value: Role("employees"), IsCollection: false },
  { value: Match(Index("letters")), IsCollection: false },
  { value: 'ten', IsCollection: false },
  { value: '10', IsCollection: false },
  { value: Time("2020-06-15T21:11:22.812Z"), IsCollection: false },
  { value: Ref(Tokens(), "1"), IsCollection: false }
]
result = client.query(
  q.map_(
    q.lambda_("x", {
      "value": q.var("x"),
      "IsCollection": q.is_collection(q.var("x")),
    }),
    [
      ["array"],
      True,
      False,
      bytearray([1, 2, 3, 4]),
      [0x1, 0x2, 0x3, 0x4],
      q.collection("Letters"),
      q.ref("credentials/self"),
      q.database("child_db"),
      q.date("2019-11-12"),
      q.ref(q.collection("Letters"), 123),
      10.1,
      q.function("double"),
      q.index("letters"),
      10,
      q.ref(q.keys(), "1"),
      q.query(q.lambda_("x", q.var("x"))),
      None,
      {"x": 10},
      q.role("employees"),
      q.match(q.index("letters")),
      "ten",
      "10",
      q.time("2020-07-06T12:34:56.789Z"),
      q.ref(q.tokens(), "1"),
    ],
  )
)
print(result)
[{'value': ['array'], 'IsCollection': False}, {'value': True, 'IsCollection': False}, {'value': False, 'IsCollection': False}, {'value': bytearray(b'\x01\x02\x03\x04'), 'IsCollection': False}, {'value': [1, 2, 3, 4], 'IsCollection': False}, {'value': Ref(id=Letters, collection=Ref(id=collections)), 'IsCollection': True}, {'value': Ref(id=282032258185953792, collection=Ref(id=credentials)), 'IsCollection': False}, {'value': Ref(id=child_db, collection=Ref(id=databases)), 'IsCollection': False}, {'value': datetime.date(2019, 11, 12), 'IsCollection': False}, {'value': Ref(id=123, collection=Ref(id=Letters, collection=Ref(id=collections))), 'IsCollection': False}, {'value': 10.1, 'IsCollection': False}, {'value': Ref(id=double, collection=Ref(id=functions)), 'IsCollection': False}, {'value': Ref(id=letters, collection=Ref(id=indexes)), 'IsCollection': False}, {'value': 10, 'IsCollection': False}, {'value': Ref(id=1, collection=Ref(id=keys)), 'IsCollection': False}, {'value': Query({'api_version': '4', 'lambda': 'x', 'expr': {'var': 'x'}}), 'IsCollection': False}, {'value': None, 'IsCollection': False}, {'value': {'x': 10}, 'IsCollection': False}, {'value': Ref(id=employees, collection=Ref(id=roles)), 'IsCollection': False}, {'value': SetRef({'match': Ref(id=letters, collection=Ref(id=indexes))}), 'IsCollection': False}, {'value': 'ten', 'IsCollection': False}, {'value': '10', 'IsCollection': False}, {'value': FaunaTime('2020-07-06T12:34:56.789Z'), 'IsCollection': False}, {'value': Ref(id=1, collection=Ref(id=tokens)), 'IsCollection': False}]
result, err := client.Query(
	f.Map(
		f.Arr{
			f.Arr{"array"},
			true,
			false,
			f.BytesV{0x01, 0x02, 0x03, 0x04},
			f.Arr{0x1, 0x2, 0x3, 0x4},
			f.Collection("Letters"),
			f.Ref("credentials/self"),
			f.Database("child_db"),
			f.Date("2019-11-12"),
			f.Ref(f.Collection("Letters"), 123),
			10.1,
			f.Function("double"),
			f.Index("letters"),
			10,
			f.Ref(f.Keys(), "1"),
			f.Query(f.Lambda("x", f.Var("x"))),
			nil,
			f.Null(),
			f.Obj{"x": 10},
			f.Role("employees"),
			f.Match(f.Index("letters")),
			"ten",
			"10",
			f.Time("2020-07-06T12:34:56.789Z"),
			f.Ref(f.Tokens(), "1"),
		},
		f.Lambda("x", f.Obj{
			"value": f.Var("x"),
			"IsCollection": f.IsCollection(f.Var("x")),
		})))

if err != nil {
	fmt.Fprintln(os.Stderr, err)
} else {
	fmt.Println(result)
}
[map[IsCollection:false value:[array]] map[IsCollection:false value:true] map[IsCollection:false value:false] map[IsCollection:false value:[1 2 3 4]] map[IsCollection:false value:[1 2 3 4]] map[IsCollection:true value:{Letters 0xc00012e210 0xc00012e210 <nil>}] map[IsCollection:false value:{280481857410171392 0xc00012e330 0xc00012e330 <nil>}] map[IsCollection:false value:{child_db 0xc00008fdd0 0xc00008fdd0 <nil>}] map[IsCollection:false value:{0 63709113600 <nil>}] map[IsCollection:false value:{123 0xc00017e000 0xc00017e000 <nil>}] map[IsCollection:false value:10.1] map[IsCollection:false value:{double 0xc00017e150 0xc00017e150 <nil>}] map[IsCollection:false value:{letters 0xc00017e270 0xc00017e270 <nil>}] map[IsCollection:false value:10] map[IsCollection:false value:{1 0xc00017e3c0 0xc00017e3c0 <nil>}] map[IsCollection:false value:{[123 34 97 112 105 95 118 101 114 115 105 111 110 34 58 34 51 34 44 34 108 97 109 98 100 97 34 58 34 120 34 44 34 101 120 112 114 34 58 123 34 118 97 114 34 58 34 120 34 125 125]}] map[IsCollection:false value:{}] map[IsCollection:false value:{}] map[IsCollection:false value:map[x:10]] map[IsCollection:false value:{employees 0xc00017e5d0 0xc00017e5d0 <nil>}] map[IsCollection:false value:{map[match:{letters 0xc00017e720 0xc00017e720 <nil>}]}] map[IsCollection:false value:ten] map[IsCollection:false value:10] map[IsCollection:false value:{789000000 63729635696 <nil>}] map[IsCollection:false value:{1 0xc00017e8d0 0xc00017e8d0 <nil>}]]
try
{
    Value result = await client.Query(
        Map(
            Arr(
                Arr("array"),
                true,
                false,
                BytesV.Of(0x1, 0x2, 0x3, 0x4),
                Arr(0x1, 0x2, 0x3, 0x4),
                Collection("Letters"),
                Ref("credentials/self"),
                Database("child_db"),
                Date("2019-11-12"),
                Ref(Collection("Letters"), 123),
                10.1,
                Function("double"),
                Index("letters"),
                10,
                Ref(Keys(), "1"),
                Query(Lambda("x", Var("x"))),
                null,
                Obj("x", 10),
                Role("employees"),
                Match(Index("letters")),
                "ten",
                "10",
                Time("2020-07-06T12:34:56.789Z"),
                Ref(Tokens(), "1")
            ),
            Lambda(
                "x",
                Obj(
                    "value", Var("x"),
                    "IsCollection", IsCollection(Var("x"))
                )
            )
        )
    );

    Console.WriteLine(result);
}
catch (Exception e)
{
    Console.WriteLine($"ERROR: {e.Message}");
}
Arr(ObjectV(value: Arr(StringV(array)),IsCollection: BooleanV(False)), ObjectV(value: BooleanV(True),IsCollection: BooleanV(False)), ObjectV(value: BooleanV(False),IsCollection: BooleanV(False)), ObjectV(value: BytesV(0x01, 0x02, 0x03, 0x04),IsCollection: BooleanV(False)), ObjectV(value: Arr(LongV(1), LongV(2), LongV(3), LongV(4)),IsCollection: BooleanV(False)), ObjectV(value: RefV(id = "Letters", collection = RefV(id = "collections")),IsCollection: BooleanV(True)), ObjectV(value: RefV(id = "295434597822366208", collection = RefV(id = "credentials")),IsCollection: BooleanV(False)), ObjectV(value: RefV(id = "child_db", collection = RefV(id = "databases")),IsCollection: BooleanV(False)), ObjectV(value: FaunaDate(2019-11-12 12:00:00 AM),IsCollection: BooleanV(False)), ObjectV(value: RefV(id = "123", collection = RefV(id = "Letters", collection = RefV(id = "collections"))),IsCollection: BooleanV(False)), ObjectV(value: DoubleV(10.1),IsCollection: BooleanV(False)), ObjectV(value: RefV(id = "double", collection = RefV(id = "functions")),IsCollection: BooleanV(False)), ObjectV(value: RefV(id = "letters", collection = RefV(id = "indexes")),IsCollection: BooleanV(False)), ObjectV(value: LongV(10),IsCollection: BooleanV(False)), ObjectV(value: RefV(id = "1", collection = RefV(id = "keys")),IsCollection: BooleanV(False)), ObjectV(value: QueryV(System.Collections.Generic.Dictionary`2[System.String,FaunaDB.Query.Expr]),IsCollection: BooleanV(False)), ObjectV(value: NullV,IsCollection: BooleanV(False)), ObjectV(value: ObjectV(x: LongV(10)),IsCollection: BooleanV(False)), ObjectV(value: RefV(id = "employees", collection = RefV(id = "roles")),IsCollection: BooleanV(False)), ObjectV(value: SetRefV(System.Collections.Generic.Dictionary`2[System.String,FaunaDB.Types.Value]),IsCollection: BooleanV(False)), ObjectV(value: StringV(ten),IsCollection: BooleanV(False)), ObjectV(value: StringV(10),IsCollection: BooleanV(False)), ObjectV(value: FaunaTime(2020-07-06T12:34:56.789Z),IsCollection: BooleanV(False)), ObjectV(value: RefV(id = "1", collection = RefV(id = "tokens")),IsCollection: BooleanV(False)))
System.out.println(
    client.query(
        Map(
            Arr(
                Arr(Value("array")),
                Value(true),
                Value(false),
                Value(new byte[] {0x1, 0x2, 0x3, 0x4}),
                Arr(Value(0x1), Value(0x2), Value(0x3), Value(0x4)),
                Collection("Letters"),
                Ref("credentials/self"),
                Database("child_db"),
                Date("2019-11-12"),
                Ref(Collection("Letters"), "123"),
                Value(10.1),
                Function("double"),
                Index("letters"),
                Value(10),
                Ref(Keys(), "1"),
                Query(Lambda("x", Var("x"))),
                Null(),
                Obj("x", Value(10)),
                Role("employees"),
                Match(Index("letters")),
                Value("ten"),
                Value("10"),
                Time("2020-07-06T12:34:56.789Z"),
                Ref(Tokens(), "1")
            ),
            Lambda(
                "x",
                Obj("value", Var("x"), "IsCollection", IsCollection(Var("x")))
            )
        )
    ).get());
[{value: ["array"], IsCollection: false}, {value: true, IsCollection: false}, {value: false, IsCollection: false}, {value: [0x01 0x02 0x03 0x04], IsCollection: false}, {value: [1, 2, 3, 4], IsCollection: false}, {value: ref(id = "Letters", collection = ref(id = "collections")), IsCollection: true}, {value: ref(id = "286816445084467712", collection = ref(id = "credentials")), IsCollection: false}, {value: ref(id = "child_db", collection = ref(id = "databases")), IsCollection: false}, {value: 2019-11-12, IsCollection: false}, {value: ref(id = "123", collection = ref(id = "Letters", collection = ref(id = "collections"))), IsCollection: false}, {value: 10.1, IsCollection: false}, {value: ref(id = "double", collection = ref(id = "functions")), IsCollection: false}, {value: ref(id = "letters", collection = ref(id = "indexes")), IsCollection: false}, {value: 10, IsCollection: false}, {value: ref(id = "1", collection = ref(id = "keys")), IsCollection: false}, {value: QueryV({api_version=4, lambda=x, expr={var=x}}), IsCollection: false}, {value: null, IsCollection: false}, {value: {x: 10}, IsCollection: false}, {value: ref(id = "employees", collection = ref(id = "roles")), IsCollection: false}, {value: {@set = {match: ref(id = "letters", collection = ref(id = "indexes"))}}, IsCollection: false}, {value: "ten", IsCollection: false}, {value: "10", IsCollection: false}, {value: 2020-07-06T12:34:56.789Z, IsCollection: false}, {value: ref(id = "1", collection = ref(id = "tokens")), IsCollection: false}]
Map(
  [
    ['array'],
    true,
    false,
    new Uint8Array([1, 2, 3, 4]),
    [0x1, 0x2, 0x3, 0x4],
    Collection('Letters'),
    Ref('credentials/self'),
    Database('child_db'),
    Date('2019-11-12'),
    Ref(Collection('Letters'), 123),
    10.1,
    Function('double'),
    Index('letters'),
    10,
    Ref(Keys(), '1'),
    Query(Lambda('x', Var('x'))),
    null,
    { x: 10 },
    Role('employees'),
    Match(Index('letters')),
    'ten',
    '10',
    Time('2020-07-06T12:34:56.789Z'),
    Ref(Tokens(), '1'),
  ],
  Lambda('x', {
    value: Var('x'),
    IsCollection: IsCollection(Var('x')),
  })
)
[
  { value: [ 'array' ], IsCollection: false },
  { value: true, IsCollection: false },
  { value: false, IsCollection: false },
  { value: { '0': 1, '1': 2, '2': 3, '3': 4 }, IsCollection: false },
  { value: [ 1, 2, 3, 4 ], IsCollection: false },
  { value: Collection("Letters"), IsCollection: true },
  {
    value: Ref(Credentials(), "302043979982045696"),
    IsCollection: false
  },
  { value: Database("child_db"), IsCollection: false },
  { value: Date("2019-11-12"), IsCollection: false },
  { value: Ref(Collection("Letters"), "123"), IsCollection: false },
  { value: 10.1, IsCollection: false },
  { value: Function("double"), IsCollection: false },
  { value: Index("letters"), IsCollection: false },
  { value: 10, IsCollection: false },
  { value: Ref(Keys(), "1"), IsCollection: false },
  { value: Query(Lambda("x", Var("x"))), IsCollection: false },
  { value: null, IsCollection: false },
  { value: { x: 10 }, IsCollection: false },
  { value: Role("employees"), IsCollection: false },
  { value: Match(Index("letters")), IsCollection: false },
  { value: 'ten', IsCollection: false },
  { value: '10', IsCollection: false },
  { value: Time("2020-07-06T12:34:56.789Z"), IsCollection: false },
  { value: Ref(Tokens(), "1"), IsCollection: false }
]
Query metrics:

  •    bytesIn:   608

  •   bytesOut: 1,679

  • computeOps:     2

  •    readOps:     0

  •   writeOps:     0

  •  readBytes:   373

  • writeBytes:     0

  •  queryTime:  29ms

  •    retries:     0

This query operates on a pre-existing schema, which is not provided here.

Also, the query is executed via a client connection, that uses a secret acquired by calling the Login function (not shown here), so that Ref("credentials/self") returns a valid value.

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