I have an expression in the format of Expression<Func<T, T2, bool>> that I need to convert into an expression on the format of Expression<Func<T2, bool>> by replacing the T in the first expression with a constant value. I need this to stay as an expression so I can't just Invoke the expression with a constant as the first parameter. I'...
Before someone shouts out the answer, please read the question through. What is the purpose of the method in .NET 4.0's ExpressionVisitor: public static ReadOnlyCollection<T> Visit<T>(ReadOnlyCollection<T> nodes, Func<T, T> elementVisitor) My first guess as to the purpose of this method was that it would visit each node in each tree ...
How to make lambda like this Action<EventHandler<TEventArgs>> adder = vs => GenericEvent += vs using expression trees. This code doesn't work: Expression<Func<EventHandler<TEventArgs>>> handler = () => GenericEvent; var vs = Expression.Parameter(typeof(EventHandler<TEventArgs>), "vs"); var adder = Expression.Lambda<Action<EventHa...
Okay first to explain the rules: I need a function that constructs a delegate matching any delegate type that encapsulates a body of which invokes a delegate of type (Object) (Object[] args) with 'args' containing all of the arguments passed to the original delegate during invocation. My work so far: delegate void TestDelegate(int...
I have a predicate, that was made from lambda expression after all extension methods were served. For example: (new List<string>).Where(i => i.Contains("some")).Where(i => i.Contains("second_some")); "List<>" is only example, there could be my custom data context or object collection. So, I have an "Expression<...>", and it's base typ...
I am trying to evaluate a list that represents an expression in prefix notation. Here is an example of such a list: [+, [sin, 3], [- 10 5]] What is the best way to evaluate the value of the list ...
Let's say I have an expression tree encoded as a linear (array) representaion. The tree is constructed from the array by "filling" the tree in level-order, left-to-right and top-to-bottom. For example, the linear representation: +*243 would parse into the following tree: + / \ / \ * 2 / \ / ...
I have a binary tree based mathematical expression parser I built, which works great for 'normal' math, like: (3.5 * 2) ^ 1 / (1 << 6). however, I would like to expand it a little to add a ternary selection operator, mirroring the one from C: {expr} ? {true-expr} : {false-expr}. I would also like to add functions, like sin(x) or ave(...)...
Hi, Given an expression that points to a property in an object graph, I want to retrieve the instance that owns the property withing that graph. I've been struggling. The current code just gives me System.InvalidOperationException : Lambda Parameter not in scope [Test] public void TestExpression() { var person = n...
What are the differences between Expression trees and CodeDom? Which should I use for which scenario? ...
I’m working on some expression tree code written by a colleague and am looking into the possibility of adding additional expressions. It currently supports: equals, not-equals, IsNull etc. I need to add something that will allow it to use a wildcard comparison similar to the SQL “Like” command or using regular expressions. At the moment ...
Is it possible to create an expression tree that directly calls a method? For example, consider the following method: public static int MyFunc(int a, int b) { return a + b; } I would like to create an expression tree that calls MyFunc with parameters a=1 and b=2. One way to accomplish this is with reflection: var c1 = Expression....
I'm writing code that evaluates .NET Expression trees. I'm trying to create a C# 4 test to exercise my handling of an ExpressionType.Index, but I can't figure out how to create that type of expression through a LambdaExpression. No matter what I try, the expression comes out as an ExpressionType.Call or ExpressionType.ArrayIndex. For ...
Hi, I am working on an ASP.Net MVC application which uses the repository pattern with linq to sql as my data source. In my repository I expose the following method: public IEnumerable<T> Find(Expression<Func<T, bool>> where) { return _context.GetTable<T>().Where(where); } I am able to call this by saying: repository<User>.Find(u...
Ok, I just don't get it. I've read about as much as I can on the subject without knowing what it's all about: Why use Expression Trees? What's a real-world example of when and how I'd use them? What overall benefit(s) are there in using them? ...
I'm building a LINQ expression tree but it won't compile because allegedly the local variable $var1 is out of scope: variable '' of type 'System.Object' referenced from scope '', but it is not defined This is the expression tree: .Block() { $var1; .If ($n.Property1 == null) { .Block() { $var1 = null; ...
I have a tree expression that looks like this: .Block( System.Object $instance, MyType2 $result) { $result = (MyType2)((MyType1)$instance).Property1; .Goto return { }; .Label .LabelTarget useDefault:; $result = .Default(MyType2); .Label .LabelTarget return:; $result } These are the custom types ...
I would have expected delegates generated from expression trees to achieve roughly the same performance as hard-coded, static, equivalent anonymous methods. However, it seems that dynamically generated delegates are noticeably slower... Here's a simple test program to illustrate the case. It just accesses 3 properties of an object 10000...
Given this code: int min = 0; Expression<Func<List<IUser>, bool>> ulContainsJohn = (l => l.Where(u => u.FirstName == "John").Count() > min); Assert.AreEqual(true, ulContainsJohn.Compile()(userList)); min = 3; Assert.AreEqual(true, ulContainsJohn.Compile()(userList)); The...
I have a method which have this signture public static IList<T> GetBy<T>(System.Linq.Expressions.Expression<Func<T, bool>> expression) i use to pass lambda expressions and make search restriction in nhibernate by reteriving data from expressiontree so when class user pass something like : c => c.fullName == "John" && c.lastName == "...