Edgar Pino

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Getting Started With Ecto Part 4: Advanced Queries

January 08, 2019

Welcome to part four of Getting Started with Ecto. On the last post, we learned how to create, read, update, and delete records with Ecto. In this post, we will learn how to write more advanced queries with Ecto.

  1. Installing and Configuring Ecto
  2. Migrations, Schemas, and Changesets
  3. CRUD operations
  4. Advanced Queries (This Post)

Relationships

On the last post, we learned how to insert a single record with no relationships. Now we are going to learn how to create records that have relationships. In this example it’s creating a user with credentials.

Let’s start by defining the Accounts module inside getting_started_with_ecto/accounts/accounts.ex. Inside of that module, we will define a function called create_users_with_credentials that takes one argument with a map as the default. In this function, we will validate the user and credentials and insert them both into the database. Here’s how that looks like:

defmodule GettingStartedWithEcto.Accounts do
  alias GettingStartedWithEcto.Accounts.{User, Credential}
  alias GettingStartedWithEcto.Repo

  def create_user_with_credentials(attrs \\ %{}) do
    %User{}
    |> User.changeset(attrs)
    |> Ecto.Changeset.cast_assoc(:credential, with: &Credential.changeset/2)
    |> Repo.insert()
  end
end

Notice the default map argument

We first pass an empty %User{} struct and the attrs to the User.changeset function to validate our data. After that, we pipe the result to the cast_assoc. This function maps the credential association, runs the Credential.changeset function, and returns a changeset with our user and credentials. Lastly, we call Repo.insert which will insert the records into the database.

Loading Associations

The Ecto.Query module

Table Joins


Edgar Pino

Software Engineer @Pluralsight. Interested in distributed systems, machine learning, and the web. Follow me on Twitter.