LINQ Expression Conversion / Concat from Int to string

Question

I want to Concat two expressions for the final expression

Expression<Func<T, string>>

So I have created expression belwo code works fine for only string types , If I get memberExpression as Int32 or DateTime throwing exception

Expression of type 'System.Int32' cannot be used for parameter of type 'System.String' of method 'System.String Concat(System.String, System.String)'

If I convert the expression as

var conversion = Expression.Convert(memberExpression, typeof (string));

getting No coercion operator is defined between types 'System.Int32' and 'System.String'.

Please help me to resolve

Code

MethodInfo bodyContactMethod = typeof (string).GetMethod("Concat",new[] {typeof (string), typeof (string)});

ParameterExpression parameter = Expression.Parameter(typeof (T));

body = Expression.Call(bodyContactMethod, cons, memberExpression);

return Expression.Lambda<Func<T, string>>(body, parameter);

Why not change your method signature to take an 'object' and just call .ToString() on everything. — Jason Sperske, Jul 25 '13 at 15:33
Hi , I am using this expression in GroupBy , so I need it in above format — ineffable p, Jul 26 '13 at 04:58

score 10 · Accepted Answer · answered Jul 25 '13 at 15:54

Instead of trying to cast to string, you could try casting to object then calling ToString(), as though you were doing:

var converted = member.ToString();

As an Expression, it will look something like this:

var convertedExpression = Expression.Call(
                     Expression.Convert(memberExpression, typeof(object)),
                     typeof(object).GetMethod("ToString"));

score 1 · Answer 2 · edited Jun 10 '19 at 06:19

1

It can be further simplified to:

var convertedExpression = Expression.Call(
                     memberExpression,
                     typeof(object).GetMethod("ToString"));

edited Jun 10 '19 at 06:19

SCouto

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answered Jun 10 '19 at 05:59

SmartCoder

856
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score 0 · Answer 3 · answered Jul 25 '13 at 15:57

0

Rather than calling string.Concat(string, string), you could try calling string.Concat(object, object):

MethodInfo bodyContactMethod = typeof (string).GetMethod("Concat", 
   new[] { typeof(object), typeof(object) });

answered Jul 25 '13 at 15:57

Richard Deeming

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well while I am using this expression in LINQ Group By , giving concat not work with types object , object – ineffable p Jul 26 '13 at 04:56

score 0 · Answer 4 · answered Nov 16 '14 at 09:35

To expand on Richard Deeming's answer even though it's a little late.

Expression.Call(
    typeof(string).GetMethod("Concat", new[] { typeof(object), typeof(object) }),
    Expression.Convert(cons, typeof(object)),
    Expression.Convert(memberExpression, typeof(object))
);

That should work just fine while allowing the signature to stay as you have it.

LINQ Expression Conversion / Concat from Int to string

4 Answers4

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