LINQ动态分配表达式

Question

I have the following code that I would rather have defined dynamically.

var candidates = People.Where(x=> (x.Age >18 && x.Age < 25)) .AsQueryable().Select(  c=> { c.Category = "F190 MISSING" ; return c; });

What I would however want is to have the above assignment defined as a string to be executed at runtime like so

String Conditional= "c=> {  c.Category = @0; return c; }";
String[]  ExpressionParameters = new [] {"F190 MISSING"};

var candidates = People.Where(x=> (x.Age >18 && x.Age < 25)).AsQueryable().Select( Conditional,ExpressionParameters);

So far, with my attempts, I have been getting either a Expression expected error message or a NO PROPERTY C EXISTS IN PERSON . How can I better define my assignment expression dynamically? Thanks in advance.

Answer 1

The first one does not work, because c# compiler is not able to transform multi-line lambda into Expression Tree (and IQueryable.Select expects expression).

The C# and Visual Basic compilers can generate expression trees only from expression lambdas (or single-line lambdas). It cannot parse statement lambdas (or multi-line lambdas). For more information about lambda expressions in C#, see Lambda Expressions (C# Programming Guide) ; (...).

The second one can be done using libraries like DynamicLINQ.