Tutorial
How to use Phoenix forms for embedded schema and JSONB
In this tutorial, I want to show you how you can setup form that stores the data in partly the columns in a database but also some of the fields in JSONB with an embedded schema.
The reason you might want to do this instead of saving all entries in separate columns is that you can add more fields without changing the database.
STEP 1 - Generate a new column
In this example, I already have setup a crud interface for products in a table called shop_products. What I need to to is to add a JSONB coulmn to that table and I will give it the generic name data.
mix ecto.gen.migration add_data_column_to_products
The way to specify a JSONB column in ecto is to add the type :map . The default is an empty map and I dont want it to be blank.
defmodule Tutorial.Repo.Migrations.AddDataToProducts do
use Ecto.Migration def change do
alter table(:shop_products) do
add :data, :map, default: %{}, null: false
end
end
end
NOTE that I dont added an index because I dont need one in this tutorial.
With the migration file in place, I need to run the migrations by:
mix ecto.migrate
STEP 2 - Add a data schema
The data will be en embedded schema with its own changeset, and if needed, its own validation rules. In this example, I want to add size and colour as additional fields to the products.
# lib/tutorial/shop/data.ex
defmodule Tutorial.Shop.Data do
use Ecto.Schema
import Ecto.Changeset @primary_key false
embedded_schema do
field :size, :string
field :color, :string
end @doc false
def changeset(option, attrs) do
option
|> cast(attrs, [:size, :color])
|> validate_required([])
end
end
In the product schema, I need to make 3 changes.
- alias the Data schema
- and an embedsone for the Data shema. Also add the onreplace: :update
- in the changeset, add the line |> cast_embed(:data)
# lib/tutorial/shop/product.ex
defmodule Tutorial.Shop.Product do
use Ecto.Schema
import Ecto.Changeset alias Tutorial.Shop.Data # <-- ADD THIS LINE @primary<i>key {:id, :binary</i>id, autogenerate: true}
@foreign<i>key</i>type :binary_id
schema "shop_products" do
field :archived<i>at, :naive</i>datetime
field :name, :string embeds<i>one :data, Data, on</i>replace: :update # <-- ADD THIS LINE timestamps()
end @doc false
def changeset(product, attrs) do
product
|> cast(attrs, [:name, :archived_at])
|> validate_required([:name])
|> cast_embed(:data) # <-- ADD THIS LINE
end
end
I can test this by putting the data as a key in the valet_attrs map. I want to test this in both create and update.
elixir
# test/tutorial/shop_test.exs
test "create_product/1 with data attributes casts and updates embedded data" do
valid_attrs = Map.put(@valid_attrs, :data, %{size: "L", color: "green"}) assert {:ok, %Product{} = product} = Shop.create<i>product(valid</i>attrs)
assert product.data.size == "L"
assert product.data.color == "green" update_attrs = Map.put(@valid_attrs, :data, %{size: "M", color: "red"})
assert {:ok, %Product{} = product} = Shop.update_product(product, update_attrs)
assert product.data.size == "M"
assert product.data.color == "red"
end
STEP 3 - Add embedded fields to the form
Since I have setup an embedsone, and that behaves as a relation, I can use fieldsfor to store the values in the data column.
When I start the app, and test the form, it looks just like the other fields. If the fields dont show up, it is most likely because the data field in the database is defaulted to NULL. Make sure that defaults to an empty map.
When that is saved, I can test this in the console by getting the last product and see that the data is there.
Shop.get_product! "3ab9f40e-b290-4a58-9311-c0d88a79eaf1"
=> %Tutorial.Shop.Product{
__meta__: #Ecto.Schema.Metadata<:loaded, "shop_products">,
archived_at: nil,
data: %Tutorial.Shop.Data{color: "Black", size: "L"},
id: "3ab9f40e-b290-4a58-9311-c0d88a79eaf1",
inserted_at: ~N[2021-06-01 08:19:21],
name: "Test",
updated_at: ~N[2021-06-01 11:13:56]
}
