mochi/input_coercion

Input value coercion and validation for GraphQL arguments.

This module validates and coerces input values (arguments, variables) against their declared types in the schema. It ensures:

Type compatibility (Int vs String, etc.)
Enum value validity
Input object field validation
Non-null constraint enforcement
List item type validation

Example

let result = input_coercion.coerce_argument_value(
  ast.StringValue("hello"),
  schema.Named("String"),
  schema,
  variables,
  ["createUser", "input", "name"],
)
// Ok(dynamic("hello"))

Types

CoercionError

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Errors that can occur during input coercion

pub type CoercionError {
  TypeMismatch(path: List(String), expected: String, got: String)
  InvalidEnumValue(
    path: List(String),
    enum_name: String,
    value: String,
  )
  MissingRequiredField(path: List(String), field: String)
  UnknownField(
    path: List(String),
    field: String,
    type_name: String,
  )
  UnknownArgument(path: List(String), name: String)
  NullNotAllowed(path: List(String))
  UnknownType(path: List(String), type_name: String)
  ScalarCoercionFailed(
    path: List(String),
    scalar_name: String,
    reason: String,
  )
}

Constructors

TypeMismatch(path: List(String), expected: String, got: String)

Value type doesn’t match expected type

InvalidEnumValue(
  path: List(String),
  enum_name: String,
  value: String,
)

Enum value is not valid for the enum type

MissingRequiredField(path: List(String), field: String)

Required field is missing from input object

UnknownField(
  path: List(String),
  field: String,
  type_name: String,
)

Unknown field provided in input object

UnknownArgument(path: List(String), name: String)

Unknown argument provided on a field

```
NullNotAllowed(path: List(String))
```
Null value provided for non-null type

UnknownType(path: List(String), type_name: String)

Referenced type not found in schema

ScalarCoercionFailed(
  path: List(String),
  scalar_name: String,
  reason: String,
)

Custom scalar rejected the value

CoercionResult

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Result of coercion - either a Dynamic value or an error

pub type CoercionResult =
  Result(dynamic.Dynamic, CoercionError)

Values

coerce_argument_value

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pub fn coerce_argument_value(
  value: @internal Value,
  expected_type: schema.FieldType,
  schema: schema.Schema,
  variables: dict.Dict(String, dynamic.Dynamic),
  path: List(String),
) -> Result(dynamic.Dynamic, CoercionError)

Coerce and validate an argument value against its declared type.

This is the main entry point for input validation. It recursively validates the value structure against the schema type definition.

coerce_arguments

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pub fn coerce_arguments(
  ast_args: List(@internal Argument),
  arg_defs: dict.Dict(String, schema.ArgumentDefinition),
  schema: schema.Schema,
  variables: dict.Dict(String, dynamic.Dynamic),
  field_path: List(String),
) -> Result(dict.Dict(String, dynamic.Dynamic), CoercionError)

Coerce all arguments for a field, returning either all coerced values or the first error

format_error

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pub fn format_error(error: CoercionError) -> String

Format a coercion error as a human-readable message