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View Source Validate Changes

In Ash, there are three kinds of validations.

- The simple `allow_nil?` and `writable?` validations provided for attributes
- Type constraints, specific to each type
- The `validations` section

##

allow_nil-writable

allow_nil/writable?

These are considered simple/global enough to warrant being specified at the attribute level.

    attributes do
      attribute :some_field, :integer, writable?: false
      attribute :some_other_field, :integer, allow_nil?: false
    end

To see the equivalent statements using the `validations` section of a resource, see the corresponding section below.

##

type-constraints

Type constraints

Each type (including custom types) can expose `constraints`. When declaring an attribute these constraints can be provided with the `constraints` option. For example:

    attributes do
      attribute :some_field, :integer, constraints: [min: 1, max: 5]
      attribute :some_other_field, :string, constraints: [max_length: 255]
    end

##

validations-section

Validations Section

The validations section allows you to create validations based on the changeset. The only information available is the changeset. If you want to adjust the behavior based on other details of the request, like the current user, you are most likely looking for authorization.

A validation is a module that implements the `Ash.Resource.Validation` behaviour. The built in validations expose utility functions that are imported into the resource's scope, to make them easier to read. You can do this with custom validations as well. See the documentation in `Ash.Resource.Validation` for more information. Right now, there are not very many built in validations, but the idea is that eventually we will have a rich library of built in validations to choose from.

Validations can be scoped to the `type` (`:create`, `:update`, `:destroy`) of action (but not to specific actions). If you would like to adjust the validations for a specific action, you can place that validation directly in the action, i.e

    create :create do
      validate attribute_equals(:name, "fred")
    end

###

important-note

Important Note

By default, validations in the global `validations` block will run on create and update only. Many validations don't make sense in the context of destroys. To make them run on destroy, use `on: [:create, :update, :destroy]`

###

examples

Examples

    validations do
      validate present([:foo, :bar]), on: :update
      validate present([:foo, :bar, :baz], at_least: 2), on: :create
      validate absent([:foo, :bar, :baz], exactly: 1), on: [:update, :destroy]
      validate {MyCustomValidation, [foo: :bar]}, on: :create
    end

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