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.

IsString

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

 
IsString( value )
is_string( value )
IsString( value )
IsString( value )
IsString( value )
IsString( value )

Description

The IsString function returns true only if value is a String, 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 String or not.

Returns

Returns a Boolean, indicating whether value was a String 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 IsString 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'),
      IsString: q.IsString(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' ], IsString: false },
  { value: true, IsString: false },
  { value: false, IsString: false },
  { value: Bytes("AQIDBA=="), IsString: false },
  { value: [ 1, 2, 3, 4 ], IsString: false },
  { value: Collection("Letters"), IsString: false },
  { value: Ref(Credentials(), "268435476221788672"), IsString: false },
  { value: Database("child_db"), IsString: false },
  { value: Date("2019-11-12"), IsString: false },
  { value: Ref(Collection("Letters"), "123"), IsString: false },
  { value: 10.1, IsString: false },
  { value: Function("double"), IsString: false },
  { value: Index("letters"), IsString: false },
  { value: 10, IsString: false },
  { value: Ref(Keys(), "1"), IsString: false },
  { value: Query(Lambda("x", Var("x"))), IsString: false },
  { value: null, IsString: false },
  { value: { x: 10 }, IsString: false },
  { value: Role("employees"), IsString: false },
  { value: Match(Index("letters")), IsString: false },
  { value: 'ten', IsString: true },
  { value: '10', IsString: true },
  { value: Time("2020-06-15T22:07:50.380Z"), IsString: false },
  { value: Ref(Tokens(), "1"), IsString: false }
]
result = client.query(
  q.map_(
    q.lambda_("x", {
      "value": q.var("x"),
      "IsString": q.is_string(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'], 'IsString': False}, {'value': True, 'IsString': False}, {'value': False, 'IsString': False}, {'value': bytearray(b'\x01\x02\x03\x04'), 'IsString': False}, {'value': [1, 2, 3, 4], 'IsString': False}, {'value': Ref(id=Letters, collection=Ref(id=collections)), 'IsString': False}, {'value': Ref(id=282032258185953792, collection=Ref(id=credentials)), 'IsString': False}, {'value': Ref(id=child_db, collection=Ref(id=databases)), 'IsString': False}, {'value': datetime.date(2019, 11, 12), 'IsString': False}, {'value': Ref(id=123, collection=Ref(id=Letters, collection=Ref(id=collections))), 'IsString': False}, {'value': 10.1, 'IsString': False}, {'value': Ref(id=double, collection=Ref(id=functions)), 'IsString': False}, {'value': Ref(id=letters, collection=Ref(id=indexes)), 'IsString': False}, {'value': 10, 'IsString': False}, {'value': Ref(id=1, collection=Ref(id=keys)), 'IsString': False}, {'value': Query({'api_version': '4', 'lambda': 'x', 'expr': {'var': 'x'}}), 'IsString': False}, {'value': None, 'IsString': False}, {'value': {'x': 10}, 'IsString': False}, {'value': Ref(id=employees, collection=Ref(id=roles)), 'IsString': False}, {'value': SetRef({'match': Ref(id=letters, collection=Ref(id=indexes))}), 'IsString': False}, {'value': 'ten', 'IsString': True}, {'value': '10', 'IsString': True}, {'value': FaunaTime('2020-07-06T12:34:56.789Z'), 'IsString': False}, {'value': Ref(id=1, collection=Ref(id=tokens)), 'IsString': 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"),
			"IsString": f.IsString(f.Var("x")),
		})))

if err != nil {
	fmt.Fprintln(os.Stderr, err)
} else {
	fmt.Println(result)
}
[map[IsString:false value:[array]] map[IsString:false value:true] map[IsString:false value:false] map[IsString:false value:[1 2 3 4]] map[IsString:false value:[1 2 3 4]] map[IsString:false value:{Letters 0xc00009be60 0xc00009be60 <nil>}] map[IsString:false value:{280481857410171392 0xc00009bf80 0xc00009bf80 <nil>}] map[IsString:false value:{child_db 0xc00013c0c0 0xc00013c0c0 <nil>}] map[IsString:false value:{0 63709113600 <nil>}] map[IsString:false value:{123 0xc00008e2a0 0xc00008e2a0 <nil>}] map[IsString:false value:10.1] map[IsString:false value:{double 0xc00008e3f0 0xc00008e3f0 <nil>}] map[IsString:false value:{letters 0xc00008e510 0xc00008e510 <nil>}] map[IsString:false value:10] map[IsString:false value:{1 0xc00008e660 0xc00008e660 <nil>}] map[IsString: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[IsString:false value:{}] map[IsString:false value:{}] map[IsString:false value:map[x:10]] map[IsString:false value:{employees 0xc00008e870 0xc00008e870 <nil>}] map[IsString:false value:{map[match:{letters 0xc00008e9c0 0xc00008e9c0 <nil>}]}] map[IsString:true value:ten] map[IsString:true value:10] map[IsString:false value:{789000000 63729635696 <nil>}] map[IsString:false value:{1 0xc00008eb70 0xc00008eb70 <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"),
                    "IsString", IsString(Var("x"))
                )
            )
        )
    );

    Console.WriteLine(result);
}
catch (Exception e)
{
    Console.WriteLine($"ERROR: {e.Message}");
}
Arr(ObjectV(value: Arr(StringV(array)),IsString: BooleanV(False)), ObjectV(value: BooleanV(True),IsString: BooleanV(False)), ObjectV(value: BooleanV(False),IsString: BooleanV(False)), ObjectV(value: BytesV(0x01, 0x02, 0x03, 0x04),IsString: BooleanV(False)), ObjectV(value: Arr(LongV(1), LongV(2), LongV(3), LongV(4)),IsString: BooleanV(False)), ObjectV(value: RefV(id = "Letters", collection = RefV(id = "collections")),IsString: BooleanV(False)), ObjectV(value: RefV(id = "295432217851593216", collection = RefV(id = "credentials")),IsString: BooleanV(False)), ObjectV(value: RefV(id = "child_db", collection = RefV(id = "databases")),IsString: BooleanV(False)), ObjectV(value: FaunaDate(2019-11-12 12:00:00 AM),IsString: BooleanV(False)), ObjectV(value: RefV(id = "123", collection = RefV(id = "Letters", collection = RefV(id = "collections"))),IsString: BooleanV(False)), ObjectV(value: DoubleV(10.1),IsString: BooleanV(False)), ObjectV(value: RefV(id = "double", collection = RefV(id = "functions")),IsString: BooleanV(False)), ObjectV(value: RefV(id = "letters", collection = RefV(id = "indexes")),IsString: BooleanV(False)), ObjectV(value: LongV(10),IsString: BooleanV(False)), ObjectV(value: RefV(id = "1", collection = RefV(id = "keys")),IsString: BooleanV(False)), ObjectV(value: QueryV(System.Collections.Generic.Dictionary`2[System.String,FaunaDB.Query.Expr]),IsString: BooleanV(False)), ObjectV(value: NullV,IsString: BooleanV(False)), ObjectV(value: ObjectV(x: LongV(10)),IsString: BooleanV(False)), ObjectV(value: RefV(id = "employees", collection = RefV(id = "roles")),IsString: BooleanV(False)), ObjectV(value: SetRefV(System.Collections.Generic.Dictionary`2[System.String,FaunaDB.Types.Value]),IsString: BooleanV(False)), ObjectV(value: StringV(ten),IsString: BooleanV(True)), ObjectV(value: StringV(10),IsString: BooleanV(True)), ObjectV(value: FaunaTime(2020-07-06T12:34:56.789Z),IsString: BooleanV(False)), ObjectV(value: RefV(id = "1", collection = RefV(id = "tokens")),IsString: 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"), "IsString", IsString(Var("x")))
            )
        )
    ).get());
[{value: ["array"], IsString: false}, {value: true, IsString: false}, {value: false, IsString: false}, {value: [0x01 0x02 0x03 0x04], IsString: false}, {value: [1, 2, 3, 4], IsString: false}, {value: ref(id = "Letters", collection = ref(id = "collections")), IsString: false}, {value: ref(id = "285736343388029440", collection = ref(id = "credentials")), IsString: false}, {value: ref(id = "child_db", collection = ref(id = "databases")), IsString: false}, {value: 2019-11-12, IsString: false}, {value: ref(id = "123", collection = ref(id = "Letters", collection = ref(id = "collections"))), IsString: false}, {value: 10.1, IsString: false}, {value: ref(id = "double", collection = ref(id = "functions")), IsString: false}, {value: ref(id = "letters", collection = ref(id = "indexes")), IsString: false}, {value: 10, IsString: false}, {value: ref(id = "1", collection = ref(id = "keys")), IsString: false}, {value: QueryV({api_version=4, lambda=x, expr={var=x}}), IsString: false}, {value: null, IsString: false}, {value: {x: 10}, IsString: false}, {value: ref(id = "employees", collection = ref(id = "roles")), IsString: false}, {value: {@set = {match: ref(id = "letters", collection = ref(id = "indexes"))}}, IsString: false}, {value: "ten", IsString: true}, {value: "10", IsString: true}, {value: 2020-07-06T12:34:56.789Z, IsString: false}, {value: ref(id = "1", collection = ref(id = "tokens")), IsString: 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'),
    IsString: IsString(Var('x')),
  })
)
[
  { value: [ 'array' ], IsString: false },
  { value: true, IsString: false },
  { value: false, IsString: false },
  { value: { '0': 1, '1': 2, '2': 3, '3': 4 }, IsString: false },
  { value: [ 1, 2, 3, 4 ], IsString: false },
  { value: Collection("Letters"), IsString: false },
  { value: Ref(Credentials(), "302043979982045696"), IsString: false },
  { value: Database("child_db"), IsString: false },
  { value: Date("2019-11-12"), IsString: false },
  { value: Ref(Collection("Letters"), "123"), IsString: false },
  { value: 10.1, IsString: false },
  { value: Function("double"), IsString: false },
  { value: Index("letters"), IsString: false },
  { value: 10, IsString: false },
  { value: Ref(Keys(), "1"), IsString: false },
  { value: Query(Lambda("x", Var("x"))), IsString: false },
  { value: null, IsString: false },
  { value: { x: 10 }, IsString: false },
  { value: Role("employees"), IsString: false },
  { value: Match(Index("letters")), IsString: false },
  { value: 'ten', IsString: true },
  { value: '10', IsString: true },
  { value: Time("2020-07-06T12:34:56.789Z"), IsString: false },
  { value: Ref(Tokens(), "1"), IsString: false }
]
Query metrics:

  •    bytesIn:   600

  •   bytesOut: 1,582

  • computeOps:     2

  •    readOps:     0

  •   writeOps:     0

  •  readBytes:   373

  • writeBytes:     0

  •  queryTime:  25ms

  •    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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