PGX Error: Cannot scan unknown type

You probably end up here because you saw this error returned from jackc/pgx

cannot scan unknown type (OID 16458) in text format into *[]recipe.CategoryType

This error is connected with custom database types, so if this is what you did, this article is for you.

I have this type in my db:

CREATE TYPE category_type AS ENUM (
  'easy',
  'medium',
  'hard'
);

Fix for pgx.Conn

When you are only using connection try below code after you connect

t, err := conn.LoadType(ctx, "category_type")
if err != nil {
    return fmt.Errorf("could not load type: %w", err)
}
conn.TypeMap().RegisterType(t)

t, err = conn.LoadType(ctx, "_category_type")
if err != nil {
    return fmt.Errorf("could not load type: %w", err)
}
conn.TypeMap().RegisterType(t)

Fix for pgxpool.Pool

When you are using connection pool fix is similar. It is impossible to load type into connection pool. You need to use custom config for your pgxpool.

config, err := pgxpool.ParseConfig(uri)
config.AfterConnect = func(ctx context.Context, conn *pgx.Conn) error {
    t, err := conn.LoadType(ctx, "category_type")
    if err != nil {
        return fmt.Errorf("could not load type: %w", err)
    }
    conn.TypeMap().RegisterType(t)

    t, err = conn.LoadType(ctx, "_category_type")
    if err != nil {
        return fmt.Errorf("could not load type: %w", err)
    }
    conn.TypeMap().RegisterType(t)

    return nil
}
if err != nil {
    return nil, fmt.Errorf("could not parse config: %w", err)
}

pool, err := pgxpool.NewWithConfig(context.Background(), config)
if err != nil {
    return nil, fmt.Errorf("could not create pool: %w", err)
}

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Hope you found this article before your 30 min google about this issue :D