How to get selected columns with repository pattern?

Question

I want to create generic method to get few columns only. I am using entity framework with repository pattern.

I tried with below

    public async Task<IEnumerable<TResult>> GetSelectedColumns<TResult>(Func<T, TResult> selector,
        Expression<Func<T, bool>> predicate = null)
    {
        IQueryable<T> query = dbSet;
        if (predicate != null)
        {
            query = query.Where(predicate);
        }
        return await query.Select(selector).ToListAsync();

    }

I am getting compile time error as below

Error CS1061 'IEnumerable<TResult>' does not contain a definition for 'ToListAsync' and no accessible extension method 'ToListAsync' accepting a first argument of type 'IEnumerable<TResult>' could be found (are you missing a using directive or an assembly reference?)

Please note; I have already included reference for Microsoft.EntityFramework

What else I am missing? is this correct way to get few columns using entity framework?

Answer 1

Change type of the selector parameter to Expression<Func<T, TResult>>. But why not simply expose the DbSet<TEntity> as an IQueryable<TEntity>?