Conversion from List(Generic1)> to List(Generic2) using C#

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Hi All..

I have two entity B1 and B2:

Entity B1:
id
List <B2>

Entity B2:
name

From the linq query i am getting the List <B1>. I have to assign a data source with the values of List <B2>

Basically i want to type cast the List <B1> into list <B2>

how can i achive this?

Posted 14-Aug-12 21:34pm

avi10788

Updated 14-Aug-12 21:37pm

v2

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StianSandberg 15-Aug-12 3:44am

Tried AutoMapper ?

2 solutions

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Philip Stuyck · Answer 1 · 2012-08-14T23:10:00

There exists a cast operator in linq, but if you were to try this you would get a cast exception. if the two classes are not in a parent child relationsship.
For instance if B2 is derived from B1, and you have a list of B1 and you know that the elements are actually B2 then you can do this cast. If you have a B2 list, then it is implicitely already a B1 list because B1 is the parent and in that case there is no need to cast.

What you have to do is this:

from b1 in b1list
select new B2(b1)

B2 has to have an extra constructor where it is able to construct itself from a B1 instance.
But there are other ways to do this as well without the need for this constructor.

from b1 in b1list
select new B2{b2field1=b1.b1field1,b2field2=b1.b1field2}

this process is called projection.

Andreas Gieriet · Answer 2 · 2012-08-14T23:48:00

Solution 2

If the type B1 can be casted to B2, you may use Cast<B2>(), e.g.

C#

List<B1> list1 = ...;
List<B2> list2 = new List<B2>(list1.Cast<B2>());

Cheers
Andi

Posted 14-Aug-12 23:48pm

Andreas Gieriet

Updated 21-Aug-12 3:48am

v3

Comments

avi10788 21-Aug-12 8:37am

new List(list1.Cast<b2>());
gives build error as List expect a parameter.

Andreas Gieriet 21-Aug-12 9:52am

Fixed: the list must have that <B2> too.
Thanks for pointing to this.

BTW: the Cast<B2>() is not even needed in .Net4:
list2 = new List<B2>(list1); is sufficient since the advent of co- and contra-variance support in C#.
Cheers
Andi