Insertable should allow Option on non null fields with default

[mackeyja92]

The Insertable trait currently does not allow fields that are specified as NOT NULL in the database but with a DEFAULT to have Option defined in the model.

For example, this model here would fail when using a postgres backend even though the database will automatically fill in the field.

#[table_name = "todos"]
#[derive(Queryable, Insertable)]
pub struct Todo {
    id: Option<i32>,
    pub description: String,
}

With the SQL definition of this

CREATE TABLE todos (
  id SERIAL PRIMARY KEY,
  description VARCHAR
);

The above SQL generates the following schema with the field being NOT NULL and having a DEFAULT.

                                                     Table "public.todos"
   Column    |       Type        |                     Modifiers                      | Storage  | Stats target | Description
-------------+-------------------+----------------------------------------------------+----------+--------------+-------------
 id          | integer           | not null default nextval('todos_id_seq'::regclass) | plain    |              |
 description | character varying |                                                    | extended |              |
Indexes:
    "todos_pkey" PRIMARY KEY, btree (id)

This should work not only for PKs but also any field that has a default in the schema.

[killercup]

We talked on Gitter about this: logs.

[sgrif]

Hm... I feel like this used to work in the past. It definitely is meant to work (with or without a default being present, which we currently don't/can't verify)