Repositories » Custom Changesets
You can define custom changeset classes that should inherit from one of the built-in types:
ROM::Changeset::CreateusesCreatecommandsROM::Changeset::UpdateusesUpdatecommandsROM::Changeset::DeleteusesDeletecommandsROM::Changesetis a generic type that needs to be configured with a specific command type that you'd like to use
Defining Changeset subclass for a specific relation
Let's say we want to generate a random access token for a user prior saving its changeset. To achieve this we can set up a custom changeset class that will do just that:
require 'securerandom'
class NewUserChangeset < ROM::Changeset::Create[:users]
map do |tuple|
tuple.merge(access_token: generate_access_token)
end
def generate_access_token
SecureRandom.hex
end
end
Now we can easily use this changeset with a user repository:
new_user = user_repo.changeset(NewUserChangeset).data(name: 'Jane')
user_repo.create(new_user)
# => #<ROM::Struct[User] id=1 name="Jane" access_token="b9dd175aec90758b0841d09e4947724e">
Re-using base changeset classes
You can inherit from your own base changeset classes to re-use common functionality. For example you may want to generate access_tokens for admins and users that are separate entities within your system. To achieve this you can define base changeset class without setting it up for any specific relation:
require 'securerandom'
class NewUserChangeset < ROM::Changeset::Create
map do |tuple|
tuple.merge(access_token: generate_access_token)
end
def generate_access_token
SecureRandom.hex
end
end
Now we can ask specific root repositories for instances of this changeset:
new_user = user_repo.changeset(NewUserChangeset).data(name: 'Jane')
user_repo.create(new_user)
# => #<ROM::Struct[User] id=1 name="Jane" access_token="b9dd175aec90758b0841d09e4947724e">
new_admin = admin_repo.changeset(NewUserChangeset).data(name: 'Jane')
admin_repo.create(new_admin)
# => #<ROM::Struct[Admin] id=1 name="Jane" access_token="b9dd175aec90758b0841d09e4947724e">
Custom changeset with a restricted relation
Changesets that inherit from Update and Delete are restrictible, which means that their
relation can (and in typical cases should be) restricted. For convenience, you can restrict
a changeset using #by_pk method, which is a common thing to do:
require 'securerandom'
class UpdateUserChangeset < ROM::Changeset::Update[:users]
map do |tuple|
tuple.merge(access_token: generate_access_token)
end
def generate_access_token
SecureRandom.hex
end
end
Now we can get our custom changeset and restrict its relation by its primary key:
user = user_repo.create(name: "Jane")
changeset = user_repo.changeset(UpdateUserChangeset).by_pk(user.id)
user_repo.update(changeset)
# => #<ROM::Struct[User] id=1 name="Jane" access_token="b9dd175aec90758b0841d09e4947724e">
You can also pass data to the restriction method:
user = user_repo.create(name: "Jane")
changeset = user_repo.changeset(UpdateUserChangeset).by_pk(user.id, name: "Jane Doe")
user_repo.update(changeset)
# => #<ROM::Struct[User] id=1 name="Jane Doe" access_token="b9dd175aec90758b0841d09e4947724e">
Using Dependency Injection with changesets
If you want to reuse various components in your changesets without coupling them too much, you can use option API
to define additional changeset collaborators. Let's say we want to provide a token generator as a changeset's collaborator
instead of implementing additional method in our changeset:
class NewUserChangeset < ROM::Changeset::Create
option :token_generator, reader: true
map do |tuple|
tuple.merge(access_token: token_generator.call)
end
end
new_user = user_repo.
changeset(NewUserChangeset).
with(token_generator: SecureRandom.method(:hex).
data(name: 'Jane')
user_repo.create(new_user)
# => #<ROM::Struct[User] id=1 name="Jane" access_token="b9dd175aec90758b0841d09e4947724e">