Phoenix/Ecto - association not working - phoenix-framework

Question

Working through a sample guide. What's detailed in the chapter doesn't work in my app. Pretty simple stuff, it would seem. I've got a Video model:
defmodule Rumbl.Video do
use Rumbl.Web, :model
schema "videos" do
field :url, :string
field :title, :string
field :description, :string
belongs_to :user, Rumbl.User
belongs_to :category, Rumbl.Category
timestamps()
end
#doc """
Builds a changeset based on the `struct` and `params`.
"""
def changeset(struct, params \\ %{}) do
struct
|> cast(params, [:url, :title, :description])
|> validate_required([:url, :title])
|> assoc_constraint(:category)
end
end
I've also got a Category model:
defmodule Rumbl.Category do
use Rumbl.Web, :model
schema "categories" do
field :name, :string
timestamps()
end
#doc """
Builds a changeset based on the `struct` and `params`.
"""
def changeset(struct, params \\ %{}) do
struct
|> cast(params, [:name])
|> validate_required([:name])
end
def alphabetical(query) do
from c in query, order_by: c.name
end
def names_and_ids(query) do
from c in query, select: {c.name, c.id}
end
end
In an IEX session, I load a Video record as so:
iex(21)> video = Repo.one(from v in Video, limit: 1)
[debug] QUERY OK source="videos" db=16.0ms
SELECT v0."id", v0."url", v0."title", v0."description", v0."user_id", v0."category_id", v0."inserted_at", v0."updated_at" FROM "videos" AS v0 LIMIT 1 []
%Rumbl.Video{__meta__: #Ecto.Schema.Metadata<:loaded, "videos">,
category: #Ecto.Association.NotLoaded<association :category is not loaded>,
category_id: nil, description: "test1", id: 2,
inserted_at: #Ecto.DateTime<2017-01-02 06:50:26>, title: "test1",
updated_at: #Ecto.DateTime<2017-01-02 06:50:26>, url: "test1 video.com",
user: #Ecto.Association.NotLoaded<association :user is not loaded>,
user_id: 10}
I get why the category and user associations are not loaded. I didn't preload the user and there isn't a category association yet to load.
Either way, I've got my video in memory:
iex(22)> v.id
2
Now I load my category:
iex(23)> category = Repo.get_by Category, name: "Comedy"
[debug] QUERY OK source="categories" db=0.0ms
SELECT c0."id", c0."name", c0."inserted_at", c0."updated_at" FROM "categories" AS c0 WHERE (c0."name" = $1) ["Comedy"]
%Rumbl.Category{__meta__: #Ecto.Schema.Metadata<:loaded, "categories">, id: 4,
inserted_at: #Ecto.DateTime<2017-01-07 07:03:00>, name: "Comedy",
updated_at: #Ecto.DateTime<2017-01-07 07:03:00>}
Just to prove that I have it:
iex(24)> category.id
4
Now I try to associate the video with the category:
iex(25)> changeset = Video.changeset(video, %{category_id: category.id})
#Ecto.Changeset<action: nil, changes: %{}, errors: [], data: #Rumbl.Video<>,
valid?: true>
iex(26)> Repo.update(changeset)
{:ok,
%Rumbl.Video{__meta__: #Ecto.Schema.Metadata<:loaded, "videos">,
category: #Ecto.Association.NotLoaded<association :category is not loaded>,
category_id: nil, description: "test1", id: 2,
inserted_at: #Ecto.DateTime<2017-01-02 06:50:26>, title: "test1",
updated_at: #Ecto.DateTime<2017-01-02 06:50:26>, url: "test1 video.com",
user: #Ecto.Association.NotLoaded<association :user is not loaded>,
user_id: 10}}
I don't understand why there aren't any changes in the changeset. This is how the guide instructs to do an association. Am I missing something?
Thanks,
John

Answer 1

I figured it out. I needed to add the category_id to the list of params in the Video model:
def changeset(struct, params \\ %{}) do
struct
|> cast(params, [:url, :title, :description, :category_id])
|> validate_required([:url, :title])
|> assoc_constraint(:category)
end