Expression Tree Tutorial - Knowledge Base (KB)
21 results in tag: dynamic
How to create an Expression<Func<dynamic, dynamic>> - Or is it a bug?
During my work with expression trees for a few days now, I came across something that I find difficult to understand; hopefully someone will be able so shed some light here....If you code ...Expression<Func<dynamic, dynamic>> expr1 = x => 2 * x;... the co...
asked by d..
C# 4 "dynamic" in expression trees
I'm trying to figure out how to put all the pieces together, and would appreciate a concrete source code sample for a simple case to start with....Consider the following C# code:...Func<int, int, int> f = (x, y) => x + y; ...I can produce an equivalent fu...
asked by Pavel Minaev
Dynamic MemberExpression
I am wanting to create a MemberExpression knowing only the field name; eg:...public static Expression<Func<TModel, T>> GenerateMemberExpression<TModel, T>(string fieldName) { PropertyInfo fieldPropertyInfo; fieldPropertyInfo = typeof(...
asked by johnnyboy
Expression.Call and Count
I'm looking for a way to do following dynamically:...var q = context.Subscription .Include("Client") .Include("Invoices") Where(s=>s.Client.Invoices.Count(i=>i.InvoiceID == SomeInt) > 0); ...I would like to bu...
asked by Max
C# linq - Change the selected field at runtime
I have an object Orders (Order, Product, Cost, Price, Client, Day). I am retrieving a lot of records from the database and to facilitate filtering, I need to pouplate DropDownLists with the distinct values retrieved so the user can select only specific da...
asked by yipiha
Creating delegates dynamically with parameter names
Hi I'm trying to create a function that dynamically creates a delegate with the same return value and the same parameters as a MethodInfo it receives as parameter and also and this is very important the same parameter names!...What I did so far is create ...
asked by Uchiha Madara
ParameterExpression of type 'System.Int32' cannot be used for delegate parameter of type 'System.String'
I'm creating a general setter using expression tree and here is my code...public Expression<Action<T,string>> GetAction<T>(string fieldName) { ParameterExpression targetExpr = Expression.Parameter(typeof(T), "Target"); MemberExpression fieldExpr...
asked by kans
Getting PropertyInfo Name and Value
I have seen various ways of doing this including reflection, component model type descriptors, expression trees, and aspects, BUT I'm still not sure whether the code below achieves all of the following objectives using .Net 4.0 or higher:...Be type safe, ...
asked by Berryl
Why does string concatenation with the + operator work with dynamic types in C#?
I recently saw an example where the following was demonstrated to work:...T Add<T>(dynamic a, dynamic b) { return a + b; } Add<string>("hello", "world"); // Returns "helloworld" ...However, if I were to attempt to use expressions to create a "generi...
asked by Matt H
Expression to create an instance with object initializer
Is there any way to create an instance of an object with object initializer with an Expression Tree? I mean create an Expression Tree to build this lambda:...// my class public class MyObject { public bool DisplayValue { get; set; } } // my lambda: v...
asked by agent47
How to instantiate and initialize a dynamic object in expression tree?
When working with ...IQuerayble<TItem>... we can call ...Select... like this:...query.Select( item => new { A=item.Prop1, B=item.Prop2}); ...And ...Select... method expects ...Expression<Func<TItem,TResult>>...I need to use ...ExpandoObject... instead of ...
asked by Pavel Voronin
Getting parameters of Func<T> variable
I have a rather complicated issue. I am trying to get a unique key from a method and its formal and actual parameters. The goal of the method, is to take a method call, and return a unique key based on 1) The name of the class and method and 2) The name a...
asked by Erik A. Brandstadmoen
Compiler Error : An expression tree may not contain a dynamic operation
Consider the following code, which wraps ...(rather than using inheritance for specific reasons)... an instance of ...Dictionary<string, T>... and implements ...IEnumerable... and ...IQueryable... so that it can be used with linq queries:...public class L...
asked by Matthew Layton
Expression Trees with dynamic parameter
I want to convert this:...Func<dynamic, object> myFunc = t => return t.Name + " " + t.Surname; ...Into an Expression Tree....What I have came up with, is this:...ParameterExpression target = ExpressionParameter(typeof(dynamic), "target"); ParameterExpress...
asked by Matias Cicero
Creating linq expression trees for dynamic objects
I am trying to build an expression tree dynamically for sorting. The sorting will happen at the action filter of my web api. So the type of object will be unknown until runtime....Here's the overview: ...At the action filter level:...IEnumerable<object> m...
asked by Newbee
Compiling statement collection to an action
So lets say I want to return an action like so ......public Action<T1, T2> BuildActionFrom(object[] stuff) { BinaryExpression[] expressions = BuildExpressions(stuff); return (x,y) => { foreach(var ex in expressions) ex(x,y); }; } ...
asked by War
Generating Action<T> with Expressions as strings
I'm trying to figure out how to generate an Action from a collection of strings the represent the actions "statement" lines ......using System.Linq.Dynamic; Action<T> BuildAction<T>(T sourceObject, T destinationObject) where T : BaseThing { var sourc...
asked by War
C# LINQ - selecting a dynamic object based on properties defined at runtime
I've been trying to create an expression which can project a strongly typed EF Core entity into a dynamic object containing a list which are defined at runtime using a REST API call....This is what I have so far:...Expression<Func<Message, dynamic>> Dynam...
asked by Stu Ratcliffe
Building dynamic lambda expressions
I know how to build a simple lambda like ...x => x > 5...:...int[] nbs = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }; IEnumerable<int> result1 = nbs.Where(x => x > 5); ParameterExpression parameter = Expression.Parameter(typeof(int), "x"); Consta...
asked by Andy Rehn
Building dynamic lambda expression
I know how to build a simple lambda like ...x => x > 5...:...int[] nbs = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }; IEnumerable<int> result1 = nbs.Where(x => x > 5); ParameterExpression parameter = Expression.Parameter(typeof(int), "x"); Consta...
asked by Andy Rehn
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