是否有更清晰简洁的方式用更好的LINQ来表达这种说法？

Question

I have two collections of elements. I am trying to take all elements in the first collection which have a matching ID in the second collection and run the CopyToDomain method against the matching elements.

The following code works fine, but I was a bit surprised by its verbosity. ReSharper isn't recommending anything here, but I was wondering if doing an intersection of the two collections and then mapping the method over the elements would be more clear? Would you make that change, or should I stop fussing and leave this as it is?

Task task = new Task();
IList<TaskAttributeDto> taskAttributeDtos = new List<TaskAttributeDto>();
taskAttributeDtos.Add(new TaskAttributeDto{ ID = 1});
taskAttributeDtos.Add(new TaskAttributeDto{ ID = 2});

foreach (TaskAttributeDto taskAttributeDto in taskAttributeDtos)
{
    TaskAttribute matching = task.TaskAttributes.FirstOrDefault(t => t.ID == taskAttributeDto.ID);
    if (matching != null)
    {
        taskAttributeDto.CopyToDomain(matching);
    }
}

Answer 1

What you're doing is basically a join, so you can use the Linq join syntax:

var matches =
    from dto in taskAttributesDtos
    join attribute in task.TaskAttributes on dto.ID equals attribute.ID
    select new { dto, attribute};

foreach (var m in matches)
    m.dto.CopyToDomain(m.attribute);

Answer 2

foreach(TaskAttributeDto taskAttributeDto in taskAttributeDtos.Where(t1 => TaskAttributes .Any(t2 => t2.Id == t1.Id)))
{
    taskAttributeDto.CopyToDomain(taskAttributeDto);
}

Answer 3

If you're concerned about the readability of query syntax, you can try using method syntax:

var matches = taskAttributesDtos.Join(task.TaskAttributes,
                                      a => a.ID,
                                      b => b.ID,
                                      (a, b) => new { dto = a, attribute = b } );

foreach (var m in matches)
    m.dto.CopyToDomain(m.attribute);

Answer 4

task.TaskAttributes.Where(t => taskAttributeDtos.Select(d => d.ID).Contains(t.ID))
    .ToList()
    .ForEach(t => taskAttributeDtos.First(d => d.ID == t.ID).CopyToDomain(t));

Answer 5

The original code finds the first match. A join finds all matches, and a group join allows you to pick a winner from each matching group.

var matches =
    from dto in taskAttributesDtos
    join attribute in task.TaskAttributes
      on dto.ID equals attribute.ID
      into attributeGroup  //into clause causes GroupJoin to be called.
    select new { dto, attribute = attributeGroup.First() };

foreach (var m in matches)
    m.dto.CopyToDomain(m.attribute);