Encountering a weird behaviour with Ecto.Changeset.unique_constraint() for multiple column, why?

Questions / Help
,
1

hello everyone,
i am encountering a weird behaviour here

my migration for id and nick_name field in user column is as follows

in file 1

defmodule MyModule.Repo.Migrations.AddInitialSchema do
  use Ecto.Migration

  def up do
    execute """
      CREATE TABLE IF NOT EXISTS `users` (
        PRIMARY KEY (`id`)
      ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
    """
  end
end

in file 2

defmodule MyModule.Repo.Migrations.UpdateColumnNickNameToUnqiueConstrainInUser do
  use Ecto.Migration

  def up do
    execute """
      ALTER TABLE users ADD UNIQUE(nick_name);
    """
  end
end

and my mysql users table look like this(only showing two field which is revelant)

+---------------------------+--------------+------+-----+---------+----------------+
| Field                     | Type         | Null | Key | Default | Extra          |
+---------------------------+--------------+------+-----+---------+----------------+
| id                        | bigint(20)   | NO   | PRI | NULL    | auto_increment |
| nick_name                 | varchar(255) | YES  | UNI | NULL    |                |
+---------------------------+--------------+------+-----+---------+----------------+

my changeset function is like this

  def changeset(user, params) do
    cast(user, params, [
      :id,
      :nick_name,
    ])
    |> unique_constraint(:nick_name,
    name: :nick_name,
    match: :suffix,
    message: "nick_name_already_taken"
    )
    |> unique_constraint(:id,
    name: :id,
    match: :suffix,
    message: "id_already_taken"
  )

my three consecutive inset is as follows

user1 = %User{
  id: 1,
  nick_name: "n1",
}

user2 = %User{
  id: 2,
  nick_name: "n1",
}

user3 = %User{
  id: 1,
  nick_name: "n2",
}

data = User.changeset(user, params)
IamService.Repo.insert(data)

now
when i am inserting user1 it is getting successfully inserted in the databases
after that when i inserting user2 i am getting error:

   errors: [
     nick_name: {"nick_name_already_taken",
      [constraint: :unique, constraint_name: "nick_name"]}
   ],

which is fine it is expected

but when i am inserting user3 i am getting the below error,

** (Ecto.ConstraintError) constraint error when attempting to insert struct:

    * PRIMARY (unique_constraint)

If you would like to stop this constraint violation from raising an
exception and instead add it as an error to your changeset, please
call `unique_constraint/3` on your changeset with the constraint
`:name` as an option.

The changeset defined the following constraints:

    * id (unique_constraint)
    * nick_name (unique_constraint)

    (ecto 3.4.4) lib/ecto/repo/schema.ex:700: anonymous fn/4 in Ecto.Repo.Schema.constraints_to_errors/3
    (elixir 1.11.4) lib/enum.ex:1411: Enum."-map/2-lists^map/1-0-"/2
    (ecto 3.4.4) lib/ecto/repo/schema.ex:685: Ecto.Repo.Schema.constraints_to_errors/3
    (ecto 3.4.4) lib/ecto/repo/schema.ex:666: Ecto.Repo.Schema.apply/4
    (ecto 3.4.4) lib/ecto/repo/schema.ex:263: anonymous fn/15 in Ecto.Repo.Schema.do_insert/4

seems to that the unique_constraint(:id,… is not getting applied
help me out, what is going wrong??

2 
* PRIMARY (unique_constraint)

Try using PRIMARY as the name for the constraint error to match on.

3

(removed by me)