# Constraint error when attempting to delete struct

#1

Hello everyone,
I have the following models and changesets for users and addresses:
user.ex

``````schema "users" do
field :title, :string
field :f_name, :string
field :l_name, :string
field :DOB, :date
field :email, :string
field :image, Assistant.Image.Type

#associations
has_many :appointment, Assistant.Web.Appointment
belongs_to :role, Assistant.Web.Role

timestamps()
end

#checks the changeset of the controller to see whether the input matches the rules I set here
def changeset(model, params \\ :invalid) do
model
|> cast(params, ~w(title f_name l_name DOB email username role_id))
|> cast_attachments(params, [:image])
|> validate_required([:title, :f_name, :l_name, :DOB, :email, :username, :role_id, :image])
|> validate_length(:username, min: 2, max: 20)
|> assoc_constraint(:role)
end
``````

``````schema "addresses" do
field :house_n, :integer
field :post_code, :string
field :city, :string
field :county, :string
field :country, :string

belongs_to :user, Assistant.Web.User, foreign_key: :user_id

timestamps()
end

@doc """
Builds a changeset based on the `struct` and `params`.
"""
def changeset(struct, params \\ %{}) do
struct
end
``````

When I try to delete a new user I have created it gives me this error:
constraint error when attempting to delete struct:

I have searched through the forum and on stack overflow and the solution seems to be to add the foreign_key_constraint(), but I am not exactly clear on how to go on about it as I have tried following the suggestions, but so far I keep getting the same error. Has it got anything to do with the cast_assoc()? I’ve got that from the book programming phoenix but online I found varying opinions on it so I thought maybe that could be the issue.

#2

Maybe You could set the on_delete option between user and its addresses association.

By default, it will do nothing… Thus I think it is why You get this error.

For this to work, You could look at

https://hexdocs.pm/ecto/Ecto.Migration.html#references/2

and

https://hexdocs.pm/ecto/Ecto.Schema.html#has_one/3

``````add :user_id, references("users"), on_delete: :delete_all
``````

and in the schema

``````has_one :addresses, Assistant.Web.Address, on_delete: :delete_all
``````

It is not tested, but it might help…

Has many belongs to relation deletion error
#3