expression-trees

问题 We have an entity of type T1 which has a member of type T . something like this : public class T1 { public T Member{get;set;} } User can use our UI to give us a filter over T and we have translate it to an expression of a function that gets a T and returns bool (Expression<Func<T,bool>>) I would like to know is it possible to convert this to an expression of a function that gets T1 and returns bool. Actually I'd like to convert this : (t=>t.Member1==someValue && t.Member2==someOtherValue); to

问题 how can I get a body from function Func<bool> methodCall = () => output.SendToFile(); if (methodCall()) Console.WriteLine("Success!"); I need to get this output.SendToFile() as a string Another example: string log = ""; public void Foo<T>(Func<T> func) { try { var t = func(); } catch (Exception) { //here I need to add the body of the lambda // log += func.body; } } public void Test() { var a = 5; var b = 6; Foo(() => a > b); } Edit: For more information on this topic see: Expression Trees 回答1

问题 I am doing a Func -> Expression -> Func conversion. It works fine if I create the Func<>() from a method(first example below) however if I create the function using an expression tree(2nd example) it fails with a NullReferenceException when accessing func2.Method.DeclaringType.FullName . And this is because DeclaringType is null. (NJection uses reflection so I think that is why it needs DeclaringType.) How can I fill in DeclaringType type for the Func<> that was created by compiling an

问题 AddOptional<tblObject>(x =>x.Title, objectToSend.SupplementaryData); private static void AddOptional<TType>(Expression<Func<TType,string>> expr, Dictionary<string, string> dictionary) { string propertyName; string propertyValue; Expression expression = (Expression)expr; while (expression.NodeType == ExpressionType.Lambda) { expression = ((LambdaExpression)expression).Body; } } In Above code i would like to get actual value of property title, not ony propert name , is it possible ? 回答1:

问题 The problem I need to solve is to run data through IF statements. The IF statements are generated by a SQL table on run time. I've managed to do this by using expressions and Lambda expressions. My table has memberName; Operator; Target. So for example I get "Age", "GreaterThan" and "40" from the table, and I compile it. var rule = new Rule(rowRule["memberName"].ToString(), rowRule["Operator"].ToString(), rowRule["Target"].ToString()); Func<User, bool> compiledRule = CompileRule<User>(rule);

问题 I'm currently making a PHP-program that solves equations. I've divided the input equation into an array so that each line in the array contains one term. (So. [0] = "+5x", [1] = "=", [2] = "-5", [3] = "+10". This is just a basic equation. The script also divides what is in () into sub-arrays. So for example 2x+(5-3x)=3(x+1) [0] = "+2*x", [1] = array([0] = "+5".... However, I discovered expression trees that is the perfect thing to use in this equation-solver. I've searched the whole internet

问题 I'm generating compiled getter methods at runtime for a given member. Right now, my code just assumes that the result of the getter method is a string (worked good for testing). However, I'd like to make this work with a custom converter class I've written, see below, "ConverterBase" reference that I've added. I can't figure out how to add the call to the converter class to my expression tree. public Func<U, string> GetGetter<U>(MemberInfo info) { Type t = null; if (info is PropertyInfo) { t

问题 Since we can: Expression<Func<int, bool>> predicate = x => x > 5; var result = Enumerable.Range(0,10).Where(predicate.Compile()); How can I: Func<int,bool> predicate = x => x > 5; Expression<Func<int,bool>> exp = predicate.Decompile(); That is, I want to get the corresponding Expression of the Func . Is it possible? 回答1: There is no magic Decompile() for a delegate instance, short of deconstructing the IL (perhaps with mono.cecil). If you want an expression tree, you'll have to start with an

问题 Following this post: link text I'm trying to create an expression tree that references the property of a property. My code looks like this: public interface IFoo { void X {get;set;} } public interface IBar : IFoo { void Y {get;set;} } public interface IFooBarContainer { IBar Bar {get;set;} } public class Filterer { //Where T = "IFooBarContainer" public IQueryable<T> Filter<T>(IEnumerable<T> collection) { var argument = Expression.Parameter(typeof (T), "item"); //... //where propertyName =

问题 Ok, I am sure this is simple, but I am having a senior moment. I have a simple BinaryExpression (greaterthan) the left side is a ParameterExpression and the right side is a ConstantExpression I want to compile this expression to a func that I can call and pass a parameter to... var func = ...something with my exp.... bool result = func(myValue); Thanks to Hasan, I modified his answer to my needs... var func = Expression.Lambda<Func<int,bool>>(myExpr, (ParameterExpression)myExpr.left).Compile(