confusing error message on constraint error

Question

Ecto is throwing me the following error:

** (exit) an exception was raised:
    ** (Ecto.ConstraintError) constraint error when attempting to insert struct:

    * unique: res_users_login_key

If you would like to convert this constraint into an error, please
call unique_constraint/3 in your changeset and define the proper
constraint name. The changeset defined the following constraints:

    * unique: res_users_login_index

Do I understand correctly that the actual name of the constraint in postgresql determines if the unique_constraint/3 function is successful or not? Just for reference, in postgreSQL the constraint is defined as follows:

Indexes:
    "res_users_pkey" PRIMARY KEY, btree (id)
    "res_users_login_key" UNIQUE CONSTRAINT, btree (login)

so _key and not _index.

I call the constraint function as follows:

 changeset |> unique_constraint(:login)

So, how do I make this work?

Try |> unique_constraint(:login, [name: :res_users_login_index]). — Dogbert
– Dogbert, Commented Apr 28, 2017 at 14:22
Do you mean: |> unique_constraint(:login, [name: :res_users_login_key])? — raarts
– raarts, Commented Apr 28, 2017 at 14:23
Oops yes, _key. _index is the incorrect name used by default since you hadn't specified a name. — Dogbert
– Dogbert, Commented Apr 28, 2017 at 14:29
Looking at stackoverflow.com/questions/4107915/… _index seems to be an inappropriate default doesn't it? Seems _key would be better for unique constraints. — raarts
– raarts, Commented Apr 28, 2017 at 14:35
They probably default to that because unique_index in Ecto migrations use the _index suffix for the index names by default. — Dogbert
– Dogbert, Commented Apr 28, 2017 at 14:41

Dogbert · Accepted Answer · 2017-04-28 14:37:42Z

3

The constraint name used by Ecto when one is not given is #{table_name}_#{field}_index. Your table is probably named res_users, and the field is login, which is why Ecto uses the constraint name res_users_login_index, which is incorrect in your case. You'll need to explicitly specify the name res_users_login_key in the call to unique_constraint:

|> unique_constraint(:login, [name: :res_users_login_key])

answered Apr 28, 2017 at 14:37

Dogbert

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