使用LINQ獲得與屬性的對象=另一個對象屬性

Question

具有以下僞代碼：

class Foo 
    { 
     public int id { get; set; } 
     public string info { get; set; } 
    } 

    class Bar 
    { 
     public int id { get; set; } 
     public int FooId { get; set; } 
     public string moreInfo { get; set; } 
    } 

    IList<Foo> foos = new List<Foo>(); 
    foos.Add(new Foo() { id = 1, info = "first!" }); 
    foos.Add(new Foo() { id = 2, info = "second!" }); 
    foos.Add(new Foo() { id = 3, info = "third!" }); 


    IList<Bar> bars = new List<Bar>(); 
    bars.Add(new Bar() { id = 1, FooId = 1, moreInfo = "Something" }); 
    bars.Add(new Bar() { id = 2, FooId = 1, moreInfo = "else" }); 
    bars.Add(new Bar() { id = 3, FooId = 2, moreInfo = "here" }); 
    bars.Add(new Bar() { id = 4, FooId = 6, moreInfo = "and" }); 
    bars.Add(new Bar() { id = 5, FooId = 7, moreInfo = "here as well" }); 

    var returnValue = select bar from bars 
         where bar.FooId IN foos.Id 

我想實現的是一個列表（我的returnValue）包含ID爲1，2和3條因爲他們的FooId在foos列表中。我怎麼弄到的？

Answer 1

var returnValue = bars.Where(b => foos.Select(f => f.Id).Contains(b.FooId); 

或者

var returnValue = from b in bars 
        join f in foos on b.FooId equals f.Id 
        select b; 

Answer 2

可以使用join clause這樣

from bar in bars 
join foo in foos on bar.FoorId equals foo.id 
select bar 

Answer 3

你可以嘗試這樣的事：

var filteredBars = bars.Join(foos, x=>x.FooId, y=>y.id, (x, y) => x);