如何在Linq中找到列表中的对象？

Question

I have a object:

public class MyObject 
    {
        public int Id { get; set; }     
        public List<MyObject> Items { get; set; }     
    }

And I have list of MyObject:

List<MyObject> collection = new List<MyObject>();

collection.Add(new MyObject()
{
     Id = 1,
     Items = null 
});

collection.Add(new MyObject()
{
     Id = 2,
     Items = null
});

collection.Add(new MyObject()
{
     Id = 3,
     Items = null
});


List<MyObject> collectionMyObject = new List<MyObject>();

collectionMyObject.Add(new MyObject()
{
     Id = 4,
     Items = collection
});

collectionMyObject.Add(new MyObject()
{
     Id = 5,
     Items = null
});

How can I find object with Id = 2 in collectionMyObject with Linq ?

Answer 1

If you are trying to find an object in collectionMyObject which has item with id 2, then this should work:

MyObject myObject = collectionMyObject.FirstOrDefault(o => o.Items != null && o.Items.Any(io => io.Id == 2));

And if you are try to find an inner item with id 2, then this query with SelectMany might be helpful:

MyObject myObject1 = collectionMyObject.Where(o => o.Items != null).SelectMany(o => o.Items).FirstOrDefault(io => io.Id == 2);

Answer 2

var item = collectionMyObject.FirstOrDefault(x => x.Id == 2);

编辑：我误解了这个问题所以安德烈的答案看起来比我的好。

Answer 3

简单：

var obj = collectionMyObject.FirstOrDefault(o => o.Id == 2);

Answer 4

Another way may be:

(from c in collection where c.Id == 2 select c).ToList;

It should give a list in return. If want a single entry, then replace ToList() with FirstOrDefault() .

Hope it helps.

Answer 5

Using the Where keyword and a lambda like so:

MyObject result = collectionMyObject.Where(x => x.Id == 2).FirstOrDefault()

Or, to find in the Items sub-collection simply do:

MyObject result = collectionMyObject.Where(x => x.Item.Id == 2).FirstOrDefault()