@spec cast_validate_params(
  Axn.Context.t(),
  keyword()
) :: {:cont, Axn.Context.t()} | {:halt, {:error, map()}}

Casts and validates parameters according to a schema with optional custom validation.

This step takes raw parameters from the context, casts them according to a schema, and optionally applies custom validation logic. The schema uses the Params library format and supports required fields, optional fields, defaults, and custom validation.

Options

• :schema - Parameter schema map (required). Uses Params.Schema format.
• :validate - Custom validation function that receives changeset (optional).

Schema Format

The schema follows the Params.Schema format:

• field!: :type - Required field of the specified type
• field: :type - Optional field of the specified type
• field: [field: :type, default: value] - Field with default value
• field: [field: :type, cast: &func/1] - Field with custom cast function

Supported types include :string, :integer, :boolean, :atom, :map, :list, etc.

Custom Validation

The optional :validate function receives an Ecto.Changeset and the current Axn.Context after initial casting and validation. It should return a modified changeset with any additional validations applied:

def validate_params(changeset, ctx) do
  changeset
  |> validate_format(:email, ~r/@/)
  |> validate_length(:name, min: 2)
  |> validate_user_permissions(ctx.assigns.current_user)
end

Context Updates

On success, this step updates the context:

• ctx.params - Contains the cast and validated parameters
• ctx.private.raw_params - Contains the original raw parameters
• ctx.private.changeset - Contains the final changeset

Examples

# Basic schema validation
step :cast_validate_params, schema: %{
  email!: :string,
  name: :string,
  age: [field: :integer, default: 18]
}

# With custom validation
step :cast_validate_params,
     schema: %{phone!: :string, region: [field: :string, default: "US"]},
     validate: &__MODULE__.validate_phone_number/2

def validate_phone_number(changeset, ctx) do
  params = Params.to_map(changeset)
  validate_format(changeset, :phone, phone_regex_for_region(params.region))
end

Returns

• {:cont, updated_context} - Parameters are valid, pipeline continues
• {:halt, {:error, %{reason: :invalid_params, changeset: changeset}}} - Validation failed

The error changeset contains all validation errors and can be used to generate user-friendly error messages.