Hello,
How do I use correctly the many_to_many association with timestamps?
I suppose it uses insert_all (or update_all) under the put_assoc and it is the reason it doesn’t provide inserted_at and modified_at.
The schemas:
defmodule A.User do
use Ecto.Schema
import Ecto.Changeset
alias A.Product
schema "users" do
field :name, :string
many_to_many :products, Product, join_through: "users_products"
timestamps()
end
@doc false
def changeset(user, attrs) do
user
|> cast(attrs, [:name])
|> validate_required([:name])
end
end
defmodule A.Product do
use Ecto.Schema
import Ecto.Changeset
schema "products" do
field :name, :string
timestamps()
end
@doc false
def changeset(product, attrs) do
product
|> cast(attrs, [:name])
|> validate_required([:name])
end
end
defmodule A.UserProduct do
use Ecto.Schema
import Ecto.Changeset
alias A.User
alias A.Product
schema "users_products" do
belongs_to :user, User
belongs_to :product, Product
timestamps()
end
@doc false
def changeset(user_product, attrs) do
user_product
|> cast(attrs, [])
|> validate_required([])
end
end
The users_products migration:
def change do
create table(:users_products) do
add :user_id, references(:users, on_delete: :nothing)
add :product_id, references(:products, on_delete: :nothing)
timestamps()
end
create unique_index(:users_products, [:user_id, :product_id])
create index(:users_products, [:user_id])
create index(:users_products, [:product_id])
end
The association:
IO.puts("querying")
product = from q in Product,
where: q.name == ^product_name
product = Repo.one(product)
IO.inspect(product, label: "product:")
IO.puts("querying")
user = from q in User,
where: q.name == ^user_name,
preload: :products
user = Repo.one(user)
IO.inspect(user, label: "user:")
if product != nil and user != nil do
cs = Ecto.Changeset.change(user)
cs = Ecto.Changeset.put_assoc(cs, :products, [product | user.products])
IO.inspect(cs, label: "assoc put")
Repo.update!(cs)
end
The error:
[debug] QUERY OK db=0.2ms queue=0.1ms
begin []
[debug] QUERY ERROR db=9.2ms
INSERT INTO "users_products" ("product_id","user_id") VALUES ($1,$2) [1, 1]
[debug] QUERY OK db=0.1ms
rollback []
** (Postgrex.Error) ERROR 23502 (not_null_violation): null value in column "inserted_at" violates not-null constraint
table: users_products
column: inserted_at
Failing row contains (4, 1, 1, null, null).
I am up with other ways to achieve this. I don’t mind to use more explicit forms, but I need flexibility to add/remove/modify the associations, for example something like:
# Check if exists
up = from q in UserProduct,
where: q.user == ^user.id and q.product == ^product.id
up = Repo.one(up)
IO.inspect(up, label: "user_product")
# Create an association
up = Products.create_user_product(%{"user_id" => 1, "product_id" => 2})
Repo.insert!(up)
But it says UserProduct contains virtual fields (belongs_to), and I don’t know if it is natural to change it to field when they don’t belong in UserProduct but User and Product.
