Ecto: Validating belongs_to association is not nil?

Questions / Help
6

I think you want the following given your schema:

def changeset(struct, params \\ %{}) do
  struct
  |> cast(params, [:rating, :place_id])
  |> validate_required([:rating]
  |> assoc_constraint(:place)
end

For a :belongs_to association, use assoc_constraint/3 for validation. It let’s Ecto check whether the Place to which the rating belongs exists. cast_assoc/3 would go on the Place schema to check Rating. Don’t use validate_required/3 to check association constraints (as instructed here).

I struggled with the different changeset validations in the same context. I outlined my findings here: Ecto Association vs Foreign Key Constraints

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