Upsert

This is a demo project to demonstrate how to integrate Ecto in a raw Mix app.

This project uses two really simple models with a one-to-one relation between them.

Setup

To start using this demo app you have to run mix deps.get to install and compile the dependencies.

You can then create the database and run migrations:

$ mix ecto.create
$ mix ecto.migrate

You'll then be able to run iex -S mix to get an interactive console with the app code loaded.

Understanding how Ecto was integrated

To discover how Ecto was integrated to the fresh mix app that was generated using mix new upsert --sup command, you can use git log -p command.

All steps are contained in a separated commit so it's easy to navigate through.

Before being able to use Ecto in your project, you have to create a "repo". It can be done by hand but there's a Mix task that can do it for you:

$ mix ecto.gen.repo

The last steps contains the creation of migrations and models and was eased by the use of Mix tasks provided by Ecto:

$ mix ecto.gen.migration create_authors
$ mix ecto.gen.migration create_posts

You should take a look at lib/author.ex and lib/post.ex.

Playing with Ecto and models

Add data

First you should create some authors and posts to play with:

%Upsert.Author{name: "Nico"} |> Upsert.Repo.insert()
%Upsert.Author{name: "Chuck"} |> Upsert.Repo.insert()

%Upsert.Post{title: "Integrating Ecto", author_id: 1} |> Upsert.Repo.insert()
%Upsert.Post{title: "Using Ecto", author_id: 2} |> Upsert.Repo.insert()

List available data

You can now list all authors and posts:

Upsert.Repo.all Upsert.Author
Upsert.Repo.all Upsert.Post

Query data

You can also get one post matching a given author_id:

import Ecto.Query
Upsert.Repo.one(from post in Upsert.Post, where: post.author_id == 1)

And you could also load this post and load the author info at the same time:

Upsert.Repo.one(from post in Upsert.Post, where: post.author_id == 1, preload: :author)

Modify existing data

Now let's say we want to change the author which is associated to a given post:

post = Upsert.Repo.one(from post in Upsert.Post, where: post.author_id == 1, preload: :author)
changed = Ecto.Changeset.change(post, %{author_id: 2})
changed |> Upsert.Repo.update()

Modifying the other way around

Now let's say we retrieve the author along with its post. We want to change the author's name and the post's title:

author = Upsert.Repo.one(from a in Upsert.Author, where: a.id == 1, preload: :post)
author_changeset = Ecto.Changeset.change(author, %{name: "New name"})
author_post_changeset = author_changeset |> Ecto.Changeset.put_assoc(:post, %{title: "New title"})
Upsert.Repo.update(author_post_changeset)

or even shorter:

author_changeset = Ecto.Changeset.change(author, %{name: "New name", post: %{title: "New title"}})
Upsert.Repo.update(author_changeset)

Moving a child from a parent to another one

There's no easy way to change a record parent from within the parent so something like the following won't work:

author_changeset = Ecto.Changeset.change(author, %{name: "New name", post: %{author_id: 2}})
Upsert.Repo.update(author_changeset)

The author_id change won't be applied on update. Ecto always takes care of associating children with their parent structure.

If you need to change the parent you have to work on the child itself:

author = Upsert.Repo.one(from a in Upsert.Author, where: a.id == 1, preload: :post)
changeset = Ecto.Changeset.change(author.post, %{author_id: 2})
Upsert.Repo.update(changeset)

Bounga/ecto_example