Please tell me how to write FirstAsync so that you can get the first element by condition. So does not work

public virtual async Task<TEntity> FindFirstAsync(Func<TEntity, Boolean> predicate) => await _dbContext.Set<TEntity>().FirstAsync<TEntity>(predicate);

    1 answer 1

    First of all, to declare a universal method , you need to do this:

     public virtual async Task<TEntity> FindFirstAsync<TEntity>(Func<TEntity, Boolean> predicate)

    That is, <TEntity> must be not only in the type of the method, but also in its name.

    Further. It is not clear from your code where the method should come from to know what _dbContext . Although, of course, this may be the field / property of the class to which the method belongs.

    Further. I understand that you want to extend the Set class so that you can do this:

     await SomeContext.SomeSet.FindFirstAsync(s => Condition(s));

    In this case, the method should be described as follows (using the “old” notation to increase readability):

     public virtual async Task<TEntity> FindFirstAsync<TEntity>(this Set<TEntity> Source, Func<TEntity, Boolean> predicate) { return await Source.FirstAsync(entity => predicate(entity)); }

    After that, you will be able to call the FindFirstAsync method on any instance of Set<T> in the manner described above. This is called the extension method.

    However, the real question is different: why do we need to declare the FindFirstAsync method in this case? Here FirstAsync does the same:

     await someContext.SomeSet.FirstAsync(s => Condition(s));

    Or a more specific example:

     await someContext.SomeSet.FirstAsync(s => s.Id == Id_From_Variable);