In the last episode, we introduced `Ecto.Multi` for transactions. I really wanted you to know about `Ecto.Multi`, but in this particular case there is an easier path we could take. Today we'll dig a bit further into that, as well as see how we can best use Ecto from Phoenix for associations. Let's get started. ## Project We're starting with the [dailydrip/firestorm repo tagged before this episode](https://github.com/dailydrip/firestorm/tree/before_episode_006.4). Right now our Schemas don't know about their associations, because the generators didn't add them. Let's fix that quickly: ```sh vim lib/firestorm_web/forums/category.ex ``` ```elixir defmodule FirestormWeb.Forums.Category do use Ecto.Schema alias FirestormWeb.Forums.Thread # <-- schema "forums_categories" do field :title, :string # Categories have many threads has_many :threads, Thread # <-- timestamps() end end ``` ```sh vim lib/firestorm_web/forums/post.ex ``` ```elixir defmodule FirestormWeb.Forums.Post do use Ecto.Schema alias FirestormWeb.Forums.{User, Thread} # <-- schema "forums_posts" do field :body, :string # Posts belong to threads belongs_to :thread, Thread # <-- # and users belongs_to :user, User # <-- timestamps() end end ``` ```sh vim lib/firestorm_web/forums/thread.ex ``` ```elixir defmodule FirestormWeb.Forums.Thread do use Ecto.Schema alias FirestormWeb.Forums.{Category, Post} # <-- schema "forums_threads" do field :title, :string # Threads belong to categories belongs_to :category, Category # and have many posts has_many :posts, Post timestamps() end end ``` ```sh vim lib/firestorm_web/forums/user.ex ``` ```elixir defmodule FirestormWeb.Forums.User do use Ecto.Schema alias FirestormWeb.Forums.Post # <-- schema "forums_users" do field :email, :string field :name, :string field :username, :string # Users have many posts has_many :posts, Post # <-- timestamps() end end ``` Now we have our relationships set up properly. From here, we can actually insert a thread with its first post without resorting to `Ecto.Multi` by including the associated post in our changeset. We'll add a new changeset function for 'new threads': ```elixir defmodule FirestormWeb.Forums do # ... defp new_thread_changeset(%{thread: thread_attrs, post: post_attrs}) do # First we'll generate a post changeset - we don't require a thread_id here # because we'll build it momentarily and it's impossible to know. post_changeset = %Post{} |> cast(post_attrs, [:body, :user_id]) |> validate_required([:body, :user_id]) # Then we'll build our thread changeset like before, but we'll put a new # associated post into the changeset. There's only one post since it's the # first one, so we make a new list with just our one post in it. %Thread{} |> thread_changeset(thread_attrs) |> put_assoc(:posts, [post_changeset]) end # ... end ``` Then we'll use this function in `create_thread`: ```elixir defmodule FirestormWeb.Forums do # ... def create_thread(category, user, attrs \\ %{}) do post_attrs = attrs |> Map.take([:body]) |> Map.put(:user_id, user.id) thread_attrs = attrs |> Map.take([:title]) |> Map.put(:category_id, category.id) %{thread: thread_attrs, post: post_attrs} |> new_thread_changeset |> Repo.insert end # ... end ``` So now this works but all of our tests are broken because we expected to get a 2-tuple back originally. Instead of making you watch me fix all that up I'll use the magic of git to introduce a fix! ```sh git checkout mid_episode_006.4 ``` Boom, now we're good. You can check out the episode script to check my work if you'd like, but it's a lot of bookkeeping. So now we're just using Ecto associations in our changesets. We know that if we send in the right sort of data, we can create a thread with a new post. But we can't actually do that yet because the UI isn't there. Let's visit [our categories index page](http://localhost:4000/categories) (making sure we're logged in). We can go into a category, and there's no means to make a thread. Not cool. We'll fix it: ```sh vim lib/firestorm_web/web/templates/category/show.html.eex ``` ```html

Show Category

<%= link "New Thread", to: category_thread_path(@conn, :new, @category) %> ``` OK, if we click the link we get a form that just asks us for a title. We know we want a body to be sent as well when we create a thread, so let's get to tweaking: ```sh vim lib/firestorm_web/web/templates/thread/new.html.eex ``` This is just the default generated form. We don't want that junk. Let's write our own 'new thread' form. I'm cheating a bit because I've already written some CSS, but you aren't here for the CSS: ```html

Start a new thread

<%= form_for @changeset, category_thread_path(@conn, :create, @category), [class: "new-thread"], fn f -> %> <%= text_input f, :title, placeholder: "Type a title" %> <%= textarea f, :body, placeholder: "Type thread content here. Use markdown syntax." %>

<%= link "Cancel", to: category_path(@conn, :show, @category), class: "pure-button button-primary -muted cancel" %> <%= submit "Create Thread", class: "pure-button button-primary reply" %>

<% end %> ``` If we use that, it works...but we aren't showing the errors any longer. We can see this if we create a post with no title. It's super confusing. Let's show the errors if they exist. Doing it with normal fields is easy: ```html

Start a new thread

<%= form_for @changeset, category_thread_path(@conn, :create, @category), [class: "new-thread"], fn f -> %> <%= text_input f, :title, placeholder: "Type a title" %> <%= error_tag f, :title %> <%= textarea f, :body, placeholder: "Type thread content here. Use markdown syntax." %>

<%= link "Cancel", to: category_path(@conn, :show, @category), class: "pure-button button-primary -muted cancel" %> <%= submit "Create Thread", class: "pure-button button-primary reply" %>

<% end %> ``` But creating a new `Thread` is also invalid if we don't pass a body for the first post. Right now we won't see that error. We can dig in a bit deeper to make this work: ```html

Start a new thread

<%= link "Cancel", to: category_path(@conn, :show, @category), class: "pure-button button-primary -muted cancel" %> <%= submit "Create Thread", class: "pure-button button-primary reply" %>

<% end %> ``` So we have a form but it's hideous. Now the css can come in, I'll paste it rather quickly. First, the action bar that I'll use a few times: ```sh vim assets/css/components/_action-bar.scss ``` ```scss .action-bar { margin-top: 1rem; display: flex; flex-direction: row; > .begin { display: flex; flex-direction: row; } > .end { justify-content: flex-end; flex-grow: 1; display: flex; flex-direction: row; align-self: flex-end; } } ``` And then the `new-thread` component: ```sh vim assets/css/components/_new-thread.scss ``` ```scss .new-thread { display: flex; flex-direction: column; > input, > textarea { border-width: 0 0 1px 0; border-color: $tower-gray; resize: vertical; margin-top: .1rem; margin-bottom: .1rem; &:focus { border-color: $sky-blue; outline: none; box-shadow: none; } } } ``` And the `button-primary` component: ```sh vim assets/css/components/_button-primary.scss ``` ```scss .button-primary { background: $punch; color: $white; &.-inverted { background: transparent; color: $punch; } &.-muted { background: transparent; color: $tundora; } } ``` Since we added new components, we'll have to restart Phoenix because [the webpack library I'm using for glob support doesn't handle new files like you'd want it to](https://github.com/Aintaer/import-glob-loader/issues/4). Once that's done, we can see that it looks a bit nicer, and we have errors. ## Summary Today we looked in a bit more detail at how to use Ecto associations with Phoenix. We also saw how error messages work in general. I hope you enjoyed it. See you soon! ## Resources - [dailydrip/firestorm tagged before this episode](https://github.com/dailydrip/firestorm/tree/before_episode_006.4) - [dailydrip/firestorm tagged smack in the middle of this episode](https://github.com/dailydrip/firestorm/tree/mid_episode_006.4) - [dailydrip/firestorm tagged after this episode](https://github.com/dailydrip/firestorm/tree/after_episode_006.4) - [Ecto.Changeset documentation](https://hexdocs.pm/ecto/Ecto.Changeset.html) - [phoenix_html documentation](https://hexdocs.pm/phoenix_html) - [issue with import-glob-loader and autoreload](https://github.com/Aintaer/import-glob-loader/issues/4)

[006.4] Using Ecto Associations in Phoenix