Ecto changeset set change movie#

Next up, we’ll add the “has one” relationship to the Movie schema: # lib/friends/movie.ex defmodule Friends.Movie do use Ecto.Schema schema 'movies' do field :title, :string field :tagline, :string has_many :characters, Friends.Character has_one :distributor, Friends.Distributor # I'm new! end end # lib/friends/distributor.ex defmodule Friends.Distributor do use Ecto.Schema schema 'distributors' do field :name, :string belongs_to :movie, Friends.Movie end end We should add a foreign key of movie_id to the distributors table migration we just generated as well as a unique index to enforce that a movie has only one distributor: # priv/repo/migrations/*_create_distributors.exs defmodule do use Ecto.Migration def change do create table ( :distributors ) do add :name, :string add :movie_id, references ( :movies ) end create unique_index ( :distributors, ) end endĪnd the Distributor schema should use the belongs_to/3 macro to allow us to call distributor.movie and look up a distributor’s associated movie using this foreign key. First, let’s generate the migration: mix create_distributors We’ll define the Distributor migration and schema with the “belongs to” relationship. Let’s say that a movie has one distributor, for example Netflix is the distributor of their original film “Bright”. Now we’re ready to run our migrations: mix ecto.migrate

This is what will allow us to call character.movie. It uses the foreign key to make a character’s associated movie available when we query for them.

In addition to adding the foreign key movie_id to our schema, it also gives us the ability to access associated movies schema through characters. Let’s take a closer look at what the belongs_to/3 macro does for us. # lib/friends/character.ex defmodule Friends.Character do use Ecto.Schema schema 'characters' do field :name, :string belongs_to :movie, Friends.Movie end end Our schema likewise needs to define the “belongs to” relationship between a character and its movie. So our migration should look like this: # priv/migrations/*_create_characters.exs defmodule do use Ecto.Migration def change do create table ( :characters ) do add :name, :string add :movie_id, references ( :movies ) end end end We can accomplish this with the following line in our create table/1 function: add :movie_id, references ( :movies ) We want this column to function as a foreign key. To declare that a character belongs to a movie, we need the characters table to have a movie_id column. A character belongs to a movie, so we’ll define a migration and schema that specifies this relationship.įirst, generate the migration: mix create_characters Now we’re ready to build our Character migration and schema.

This is what will allow us to call movie.characters. What it does is use the foreign key on the associated schema, characters, to make a movie’s associated characters available. The has_many/3 macro doesn’t add anything to the database itself. # lib/friends/movie.ex defmodule Friends.Movie do use Ecto.Schema schema 'movies' do field :title, :string field :tagline, :string has_many :characters, Friends.Character end end We’ll add a schema that specifies the “has many” relationship between a movies and its characters. Open up the newly generated migration file and define your change function to create the movies table with a few attributes: # priv/repo/migrations/*_create_movies.exs defmodule do use Ecto.Migration def change do create table ( :movies ) do add :title, :string add :tagline, :string end end end Let’s generate a migration for Movie: mix create_movies We’ll implement a “has many/belongs to” relationship between these two schemas: A movie has many characters and a character belongs to a movie. We’ll start with two schemas: Movie and Character. We’re adding some new entities to our Friends app’s domain model so that we can catalogue our favorite films.

Ecto changeset set change how to#

We’ll look at what they are and how to implement each type of relationship. There are three types of associations we can define between our schemas.

You can refer to the setup here for a quick refresher. We’ll start off with the same Friends app from the previous lesson.