Select from multiple list using LINQ

Question

I have multiple list of class.

public class MainClass
{
 public List<A> a{ get; set; }
 public List<B> b{ get; set; }
 public List<C> c{ get; set; }
}

And main class contains following property

 class A
    {
      public string Name{ get; set; }
      public string MainAddress{get;set;}
    }

    class B
    {
      public int ID {get;set;}
      public string Address{ get; set; }
    }

    class C
    {
     public int ID {get;set;}
      public string Name{ get; set; }
    }

Now how do i fetch data from List b & c and pass it to A This is what i tried

  List<A> query = (from b in MainClass.b
               join c in Mainclass.c
                on b.ID equals c.ID
                select new {b.Address, c.Name});

How do i display Name from C as MainAddress in A

What you need is a JOIN operation between them, based on their ID property they both have. The answer to this question gives you that: [How to do a join in linq to sql with method syntax?](http://stackoverflow.com/questions/3217669/how-to-do-a-join-in-linq-to-sql-with-method-syntax) — Avner Shahar-Kashtan, Apr 29 '15 at 10:15
@AvnerShahar-Kashtan I am not asking how to join, i am just asking how do i display from one list to another — Richa, Apr 29 '15 at 10:16
It's not clear what you're trying to do. `select new {b.B, c.C}` does not compile since `B` and `C` don't have properties `B` and `C`. Do you want to initialize `MainClass.a` with all linked `Name+Address` properties of the other collections? If so, how do you want to build the `MainAddress`? — Tim Schmelter, Apr 29 '15 at 10:16
`on a.ID equals b.ID` is invalid as `a` has not been defined anywhere. — Andy Nichols, Apr 29 '15 at 10:18
@Richa: it's still not clear, how do you want to construct `MainAddress`? — Tim Schmelter, Apr 29 '15 at 10:19
@TimSchmelter MainAddress should contain data fetched from Address in B — Richa, Apr 29 '15 at 10:22

Sam Aleksov · Answer 1 · 2015-04-29T10:47:33.107

Correct me if I'm wrong but I think that what you want is a List of A having MainAddresses comming from the c list. If so:

 var query = (from b in MainClass.b
               join c in Mainclass.c
                on b.ID equals c.ID
                select new A { MainAddress = c.Name });

Edit: I went ahead and made a full working example so that you can check your mistakes...

A, B, and C classes must have the same visibility as a, b, and c properties.
You are accessing b and c statically but they are instance variables.

Of course the transformation from Enumerable to List can be made in one step by calling the ToList selector directly on the Enumerable instance.

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var mainClass = new MainClass();

            mainClass.b = new List<B>();
            mainClass.c = new List<C>();
            mainClass.b.Add(new B { ID = 1, Address = "B1" });
            mainClass.c.Add(new C { ID = 1, Name = "C1" });

            //using LINQ
            var query = (from b in mainClass.b
                         join c in mainClass.c
                          on b.ID equals c.ID
                         select new A { MainAddress = c.Name });

            List<A> fromLINQ = query.ToList();

            //using anonymous functions aka lambda expressions
            IEnumerable<A> enumerableFromAnonymous = mainClass.b.Join(mainClass.c, x => x.ID, x => x.ID, (x, y) => { return new A() { MainAddress = y.Name }; });
            List<A> listFromAnonymous = enumerableFromAnonymous.ToList();
        }
    }

    public class MainClass
    {
        public List<A> a { get; set; }
        public List<B> b { get; set; }
        public List<C> c { get; set; }
    }

    public class A
    {
        public string Name { get; set; }
        public string MainAddress { get; set; }
    }

    public class B
    {
        public int ID { get; set; }
        public string Address { get; set; }
    }

    public class C
    {
        public int ID { get; set; }
        public string Name { get; set; }
    }
}

The query seems fine. A must be visible in the code where you are using the statement. It returns an IEnumerable of A and as Tim commented above it can be enumerated to a List of A with query.ToList(). — Sam Aleksov, Apr 29 '15 at 10:25
@Jaycee who said ToList can be called twice? In fact nowhere in my code ToList is called more than once on the same Enumerable... — Sam Aleksov, Apr 29 '15 at 12:27

score 2 · Accepted Answer · answered Apr 29 '15 at 10:27

Heres a complete Snippet of the demo code: http://share.linqpad.net/aq8f6c.linq

To get the address from B displayed as the Mainadress in A do the following:

var result = from a in As
             join b in (from b in Bs
                        join c in Cs
                        on b.ID equals c.ID
                        select new {b.Address, c.Name})
             on a.Name equals b.Name
             select new A {
                 Name = a.Name,
                 MainAddress = b.Address
             };

result then is of type Ienumerable<A>.

Output:

enter image description here

score 0 · Answer 3 · answered Apr 29 '15 at 11:18

I thought Serv's example was the correct answer but I did not like the query syntax as I find this more difficult to read and maintain due to Visual Studio's inability to support Lambda expressions in the immediate window - as of VS2013.

I prefer method syntax using an intermediate variable. This saves screen space and I think it is easier to understand:

   var query = from a in As
                join c in (from b in Bs
                           join c in Cs
                           on b.ID equals c.ID
                           select new {b.Address, c.Name})
                on a.Name equals c.Name
                select new A {
                    Name = a.Name,
                    MainAddress = c.Address
                };
    query.Dump();

    //method sytnax
    var nameAddress = Bs.Join(Cs, b => b.ID, c => c.ID, (b, c) => new { Name = c.Name, Address = b.Address });
    var query2 = As.Join(nameAddress, a => a.Name, na => na.Name, (a, na) => new { Name = a.Name, MainAddress = na.Address});
    query2.Dump();

Select from multiple list using LINQ

3 Answers3