Ecto.Validator

Validates a given struct or dict given a set of predicates.

Ecto.Validator.struct(user,
  name: present() when on_create?(user),
  age: present(message: "must be present"),
  age: greater_than(18),
  also: validate_other
)

Validations are passed as the second argument in the attribute-predicate format. Each predicate can be filtered via the when operator. Note when here is not limited to only guard expressions.

The predicates above are going to receive the attribute being validated and its current value as argument. For example, the present predicate above is going to be called as:

present(:name, user.name)
present(:age, user.age, message: "must be present")

The validator also handles a special key :also, which is used to pipe to predicates without a particular attribute. Instead, such predicates receive the struct as argument. In this example, validate_other will be invoked as:

validate_other(user)

Note all predicates must return a keyword list, with the attribute error as key and the validation message as value.

A handful of predicates can be found at Ecto.Validator.Predicates.