1

I need string conversion of an Expression Tree so

I create an Expression Tree and use ToString method like this

var exp = ((Expression<Func<UserDetailInfo, bool>>) (x => x.OperationID == operationId)).ToString();

but result is strange 

x => (x.OperationID == value(TCS.Proxy.PermissionProxy+<>c__DisplayClass5).operationId)

TCS.Proxy.PermissionProxy is my class in WCF proxy project !!! (I send expression from client to proxy)

but when I create this Expression myself everything is good

var entity = Expression.Parameter(typeof(UserDetailInfo));
var constant = Expression.Constant(operationId);
var e = Expression.Equal(Expression.Property(entity, "OperationID"), constant);
var exp = Expression.Lambda<Func<UserDetailInfo, bool>>(e, entity).ToString();

and result is ok

Param_0 => (Param_0.OperationID == operationId) // I Need this

How I can use ToString() can generates result like above ?

Why two results is different ?

* I Convert Expression to String for transfer it from client to WCF service so I need correct string for convert in server side from string to Expression

Peter Ritchie
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Hamed F
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1 Answers1

1

This is because your right hand side member is not a constant, it is a captured variable. The TCS.Proxy.PermissionProxy+<>c__DisplayClass5 part means in the class TCS.Proxy.PermissionProxy it had to create 5 new classes that holds values that where passed in via variable capture and this specific lambda uses the 5th one it created.

Your code (You never show your function so I made some guesses)

namespace TCS.Proxy
{
    class PermissionProxy
    {
         public void SomeFunction()
         {
             int operationId = 0;
             var exp = ((Expression<Func<UserDetailInfo, bool>>) (x => x.OperationID == operationId)).ToString()
         }
    }
}

Is getting re-written to something similar (It's actually a lot different but this example gets the point across) to

namespace TCS.Proxy
{
    public class PermissionProxy
    {

         private class c__DisplayClass5
         {
             public int operationId;
         }

         public void SomeFunction()
         {
             int operationId = 0;

             var <>c__DisplayClass5 = new c__DisplayClass5();
             <>c__DisplayClass5.operationId = operationId;

             var exp = ((Expression<Func<UserDetailInfo, bool>>) (x => x.OperationID == <>c__DisplayClass5.operationId)).ToString()
         }
    }
}

Which is different than what you manually created. If you want to "unbox" these custom classes you will need to write up a ExpressionVisitor that will go through the expression and re-write it in to the form you want to go over the wire.

Scott Chamberlain
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  • Can you suggest a way for convert strange string to correct string ? for example modify string to convert to correct mode ? – Hamed F May 04 '14 at 19:21
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    Yes, you will need to write a `ExpressionVisitor` class that performs the re-write. I linked a tutorial on how to write on in the answer. Here is a more [simple tutorial](http://pelebyte.net/blog/2011/05/13/doing-simple-things-with-expressionvisitor/) – Scott Chamberlain May 04 '14 at 19:42
  • @Chamberlain Can you suggest me a way for convert string to expression tree and visa versa ??? I want Send an Expression from client to wcf proxy then convert Expression to string and send to WCF service (Expression is not serializable) in service convert string to Expression for using LINQ in WCF Services ?!?! I want to use Serialize.Linq library but does not work ! http://stackoverflow.com/questions/23435468/serialize-linq-does-not-work-in-wcf-proxy-layer – Hamed F May 04 '14 at 19:46