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Crecto provides validations and constraints which are turned into changeset errors.

Validations are performed without the need to interact with the database.

class User < Crecto::Model
schema "users" do
field :uuid, String
field :age, Int32
field :name, String
field :role, String
field :password, String, virtual: true
field :password_confirmation, String, virtual: true
# Validate that fields arent blank before inserting or updating
validate_required :age # or an array [:age, :name]
# Validate the format of fields using a regex
validate_format :name, /^[a-zA-Z]*&/
# Validate the length of a field
validate_length :uuid, is: 36, # min: 36, max: 60
# Validate the existence of the value of the field in an array
validate_inclusion :role, in: ["admin", "user"]
# Opposite of inclusion
validate_exclusion :age, in: Range(0, 20)
# Generic or custom validation using a proc
validate "Passwords must match", ->(user: User) do
user.password == user.password_confirmation
# Multiple validations
validates :name,
presence: true,
format: {pattern: /^[a-zA-Z]*&/},
exclusion: {in: ["foo", "bar"]},
length: {min: 2, max: 50}