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.

`Let`

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

Let( bindings, in )

let( bindings, in )

Let( bindings, in )

Let( bindings, in )

Let( bindings, in )

Let( bindings, in )

Description

The Let function binds one or more variables to a single value or expression. When multiple variables are defined, the evaluation is from left to right. Variables which have previously been defined may be used to define future variables. Variables are lexically scoped to the expression passed via the in parameter. The value of a variable can be referenced with Var syntax.

Parameters

Parameter Type Definition and Requirements

Parameter	Type	Definition and Requirements
`bindings`	List of pairs	The variable or variables to define.
`in`	Expression	The expression in which the variables are defined.

bindings

List of pairs

The variable or variables to define.

in

Expression

The expression in which the variables are defined.

Returns

The evaluation of the in argument.

Examples

The following query defines two variables to be used by the expression defined by the in argument. The first variable "x" contains the value 1 and the second variable "y" contains the value 2. The expression defined by the in argument simply returns the value of the variable "x". The value is accessed by using the Var function with the associated variable’s name.

client.query(
  q.Let(
    { x: 1, y: 2 },
    q.Var('x')
  )
)
.then((ret) => console.log(ret))
.catch((err) => console.error(
  'Error: [%s] %s: %s',
  err.name,
  err.message,
  err.errors()[0].description,
))

result = client.query(
  q.let({"x": 1, "y": 2}, q.var("x"))
)
print(result)

result, err := client.Query(
	f.Let().Bind(
		"x", 1).Bind(
		"y", 2).In(
		f.Var("x")))

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

try
{
    Value result = await client.Query(
        Let("x", 1, "y", 2).In(Var("x"))
    );
    Console.WriteLine(result);
}
catch (Exception e)
{
    Console.WriteLine($"ERROR: {e.Message}");
}

LongV(1)

System.out.println(
    client.query(
        Let("x", Value(1), "y", Value(2)).in(Var("x"))
    ).get());

Let(
  { x: 1, y: 2 },
  Var('x')
)

Query metrics:

bytesIn: 42
bytesOut: 14
computeOps: 1
readOps: 0
writeOps: 0
readBytes: 0
writeBytes: 0
queryTime: 1ms
retries: 0

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