Represents a validation in Ash.

See Ash.Resource.Validation.Builtin for a list of builtin validations.

To write your own validation, define a module that implements the init/1 callback to validate options at compile time, and validate/2 callback to do the validation.

Then, in a resource, you can say:

validations do
  validation {MyValidation, [foo: :bar]}
end

To make it more readable, you can define a function in the module that returns that tuple, and import it into your resource.

defmodule MyValidation do
  def my_validation(value) do
    {__MODULE__, foo: value}
  end
end

defmodule MyResource do
  ...

  import MyValidation

  validations do
    validate my_validation(:foo)
  end
end