expression-trees

问题 At point (3) in my code I have defined a query called query1 in which I defined a .Where lambda expression. This query is in some way dynamic but still contains static elements, it always refers to the Type Employee and its (int) property ClientID. Now I very much like to make the refering to the type and its property dynamic, based on the method parameters which by example are shown below point (1). What I tried to so far is making the static part of the query defined under point (3) fully

问题 I'm trying to generate the following LINQ query: //Query the database for all AdAccountAlerts that haven't had notifications sent out //Then get the entity (AdAccount) the alert pertains to, and find all accounts that //are subscribing to alerts on that entity. var x = dataContext.Alerts.Where(a => a.NotificationsSent == null) .OfType<AdAccountAlert>() .ToList() .GroupJoin(dataContext.AlertSubscriptions, a => new Tuple<int, string>(a.AdAccountId, typeof(AdAccount).Name), s => new Tuple<int,

问题 This would be very simple if I were able to assign via a Lambda expression (below) //An expression tree cannot contain an assignment operator Expression<Func<ComplexObj, object>> expression = obj => obj.Contacts[0].FirstName = "Tim"; This code above is invalid due to the assignment operator. I need to pass a lambda expression in order to identify the property in the complex object that needs to be set. In some cases the complex object has List and therefor duplicate object types and names

问题 I'm building a SQL "WHERE" clause dynamically using the System.Linq.Expressions.Expression class. It works well for simple clauses, e.g. to add "PhaseCode = X" clause, I do the following: var equalTarget = Expression.Constant(phaseCode, typeof(int?)); var phaseEquals = Expression.Equal(Expression.PropertyOrField(projParam, "PhaseCode"), equalTarget); However, now I'm trying to build an expression that will returns the record if a project has been assigned to a particular group. Project and

问题 This question already has answers here : How do I create an expression tree to represent 'String.Contains(“term”)' in C#? (4 answers) Closed 5 years ago . I'm struggling to build an expression tree so I can dynamically do filtering on some data. I have come up with this, but it fails at the var lambda = line foreach (var rule in request.Where.Rules) { var parameterExpression = Expression.Parameter(typeof(string), rule.Field); var left = Expression.Call(parameterExpression, typeof(string)

问题 I have some expirience with .Net Expressions , when I'm able to dynamically generate methods. It's fine, it's good. But now I need to generate a whole class, and it seems that the only way to do it is Emit whole IL which is totally inacceptable (it's impossible to support). Assume we have following interface: public interface IFoo { [Description("5")] int Bar(); [Description("true")] bool Baz(); } which should be converted to: public class Foo : IFoo { public int Bar() => 5; public bool Baz()

问题 I am currently porting a .NET codebase in MonoTouch and I'm currently working on a method that receives an Expression<T> . I'm trying to compile it, and then dynamically invoke it. Here's what I did: // Here's an example of what I could receive Expression<Action<int>> expression = (a => Console.WriteLine (a * 2)); // And here's what I'm trying to do to invoke it expression.Compile().DynamicInvoke(6); This works fine in the iOS Simulator, the result "12" is printed in my console. But then I

问题 I am trying to write a static function to Or two expressions, but recieve the following error: The parameter 'item' is not in scope. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.InvalidOperationException: The parameter 'item' is not in scope. the method: public static Expression<Func<T, bool>> OrExpressions

问题 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"); ParameterExpression result = ExpressionParameter(typeof(object), "result"); BlockExpression block = Expression.Block( new [] { result }, Expression.Assign( result, Expression.Add( Expression.Add( Expression.Property(target, "Name"), Expression.Constant(" ", typeof

问题 This is best explained using code. I have a generic class that has a method that returns an integer. Here is a simple version for the purposes of explaining... public class Gen<T> { public int DoSomething(T instance) { // Real code does something more interesting! return 1; } } At runtime I use reflection to discover the type of something and then want to create an instance of my Gen class for that specific type. That is easy enough and done like this... Type fieldType = // This is the type I