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.

`ContainsField`

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

ContainsField( field, in )

contains_field( field, in )

ContainsField( field, in )

ContainsField( field, in )

ContainsField( field, in )

ContainsField( field, in )

Description

The ContainsField function returns true if the specified field exists within the result of the in expression, or false otherwise.

ContainsField is useful when you need to distinguish between objects, arrays, or documents that contain a field and those that do not.

Parameters

Parameter Type Definition and Requirements

Parameter	Type	Definition and Requirements
`field`	String	The name of a field.
`in`	Any	A value of any type.

field

String

The name of a field.

in

Any

A value of any type.

Returns

A boolean value indicates whether field exists within in.

Examples

The following query returns true because the field a exists in the provided object:

client.query(
  q.ContainsField(
    'a',
    {
      a: 1,
      b: 2,
      c: 3,
    },
  )
)
.then((ret) => console.log(ret))
.catch((err) => console.error(
  'Error: [%s] %s: %s',
  err.name,
  err.message,
  err.errors()[0].description,
))

true

result = client.query(
  q.contains_field(
    "a",
    {
      "a": 1,
      "b": 2,
      "c": 3
    }
  )
)
print(result)

True

result, err := client.Query(
	f.ContainsField(
		"a",
		f.Obj{
			"a": 1,
			"b": 2,
			"c": 3 }))

if err != nil {
	fmt.Fprintln(os.Stderr, err)
} else {
	fmt.Println(result)
}

true

try
{
    Value result = await client.Query(
        ContainsField(
            "a",
            Obj(
                "a", 1,
                "b", 2,
                "c", 3
            )
        )
    );

    Console.WriteLine(result);
}
catch (Exception e)
{
    Console.WriteLine($"ERROR: {e.Message}");
}

BooleanV(True)

System.out.println(
    client.query(
        ContainsField(
            Value("a"),
            Obj(
                "a", Value(1),
                "b", Value(2),
                "c", Value(3)
            )
        )
    )
    .get());

true

ContainsField(
  'a',
  {
    'a': 1,
    'b': 2,
    'c': 3,
  },
)

true

Query metrics:

bytesIn: 58
bytesOut: 17
computeOps: 1
readOps: 0
writeOps: 0
readBytes: 0
writeBytes: 0
queryTime: 5ms
retries: 0

The following query returns false because the field f does not exist in the provided object:

client.query(
  q.ContainsField(
    'f',
    {
      a: 1,
      b: 2,
      c: 3,
    },
  )
)
.then((ret) => console.log(ret))
.catch((err) => console.error(
  'Error: [%s] %s: %s',
  err.name,
  err.message,
  err.errors()[0].description,
))

false

result = client.query(
  q.contains_field(
    "f",
    {
      "a": 1,
      "b": 2,
      "c": 3
    }
  )
)
print(result)

False

result, err := client.Query(
	f.ContainsField(
		"f",
		f.Obj{
			"a": 1,
			"b": 2,
			"c": 3 }))

if err != nil {
	fmt.Fprintln(os.Stderr, err)
} else {
	fmt.Println(result)
}

false

try
{
    Value result = await client.Query(
        ContainsField(
            "f",
            Obj(
                "a", 1,
                "b", 2,
                "c", 3
            )
        )
    );

    Console.WriteLine(result);
}
catch (Exception e)
{
    Console.WriteLine($"ERROR: {e.Message}");
}

BooleanV(False)

System.out.println(
    client.query(
        ContainsField(
            Value("f"),
            Obj(
                "a", Value(1),
                "b", Value(2),
                "c", Value(3)
            )
        )
    )
    .get());

false

ContainsField(
  'f',
  {
    'a': 1,
    'b': 2,
    'c': 3,
  },
)

false

Query metrics:

bytesIn: 58
bytesOut: 18
computeOps: 1
readOps: 0
writeOps: 0
readBytes: 0
writeBytes: 0
queryTime: 6ms
retries: 0

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