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elixirphoenix-frameworkecto

Tds adapter supports only on_conflict: :raise (insert using on_conflict option)

Im on phoenix tutorial but using the Tds adapter (SQL Server), at the shopping cart behavior. The code fails using the on_conflict option for insert, here is the code

def add_item_to_cart(%Cart{} = cart, %Catalog.Product{} = product) do
    %CartItem{quantity: 1, price_when_carted: product.price}
    |> CartItem.changeset(%{})
    |> Ecto.Changeset.put_assoc(:cart, cart)
    |> Ecto.Changeset.put_assoc(:product, product)
    |> Repo.insert(
      on_conflict: [inc: [quantity: 1]],
      conflict_target: [:cart_id, :product_id]
    )
  end

The error is Tds adapter supports only on_conflict: :raise I'm trying to follow the tutorial and want to know if it is a dead-end or if there is an alternative to achieve the same.

Solution

  • There are three alternatives.

    • use what the host DB supports (on_conflict: :raise), rescue the raised exception, and execute another query that would increase quantity by 1 from rescue clause
    • start with issuing select query for [:cart_id, :product_id] and if it returned an empty result, call add_item_to_cart/2, otherwise increase quantity by 1
    • [the best one] use the database that is recommended for this tutorial (e. g. PostgreSQL)