How to handle exceptions in async methods that return Task<Something>

Question

I am taksed to introduce exception logging in a layer of middleware. From top to bottom of this middleware the calls are as follows:

//In layer C
public async Task<List<Foo>> GetFoo(GetFooRequest request)
{
    return await _repository.GetFooAsync(request);
} 

//In layer D
public async Task<List<Foo>> GetFooAsync(GetFooRequest request)
{
    return await _context.Foo.Where(x=> x.FooId=request.FooID).ToListAsync();
} 

I would like to log in Layer C, however, Task returns a System.Void, as such the compiler complains about the code below. I understand why the code below fails but I am having problems finding a solution pattern or practice of logging in layer C.

 //In layer C
public async Task<List<Foo>> GetFoo(GetFooRequest request)
{
    try
    {
        return await _repository.GetFooAsync(request);
    }
    catch(Exception e)
    {
        base.LogException(e)      //<- Not all code paths return a value
    }
} 

Is there a way I can create a class that Invokes methods and do logging there, such as return await LogInvoker.Invoke(_repository.GetFooAsync...) ? Or does this require refactoring the current flow between the layers?

Answer 1

You've got to do something at the end of the catch block. You mention in the question comments that you'd be prepared to return an empty list if something goes wrong:

public async Task<List<Foo>> GetFoo(GetFooRequest request)
{
    try
    {
        return await _repository.GetFooAsync(request);
    }
    catch(Exception e)
    {
        base.LogException(e);
        return new List<Foo>();
    }
} 

or rethrow the exception, if that makes sense to your application:

public async Task<List<Foo>> GetFoo(GetFooRequest request)
{
    try
    {
        return await _repository.GetFooAsync(request);
    }
    catch(Exception e)
    {
        base.LogException(e);
        throw;
    }
}