Expression Tree Tutorial - Knowledge Base (KB)
56 results in tag: expression
Expression.Or, The parameter 'item' is not in scope
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 ...
asked by ccook
Bit Curious to understand Expression Tree in .NET
I have read several articles and several ...stackoverflow.com... posts about expression tree. It is beating my brain to understand....Questions:... 1) Like DOM (Document Object Model), it is an in-memory representation of logic?...2) Somebody explained it...
asked by user192142
C#: An item with the same key has already been added, when compiling expression
Ok, here's a tricky one. Hopefully there is an expression guru here who can spot what I am doing wrong here, cause I am just not getting it....I am building up expressions that I use to filter queries. To ease that process I have a couple of ...Expression...
asked by Svish
Create New Expression from Existing Expression
I have an ...Expression<Func<T,DateTime>>... I want to take the DateTime part of the expression and pull the Month off of it. So I would be turning it into a ...Expression<Func<T,int>>... I'm not really sure how to do this. I looked at the ...ExpressionTr...
asked by Adam
Calling a Generic Method using Lambda Expressions (and a Type only known at runtime)
You can use ...Lambda Expression Objects... to represent a lambda as an expression....How do you create a ...Lambda Expression Object... representing a generic method call, if you only know the type -that you use for the generic method signature- at runt...
asked by SDReyes
Why is Func<> created from Expression<Func<>> slower than Func<> declared directly?
Why is a ...Func<>... created from an ...Expression<Func<>>... via .Compile() considerably slower than just using a ...Func<>... declared directly ?...I just changed from using a ...Func<IInterface, object>... declared directly to one created from an ...E...
asked by MartinF
Convert Linq to Sql Expression to Expression Tree
Can anyone convert this simple LINQ-to-SQL to an Expression Tree:...List<Region> lst = (from r in dc.Regions where r.RegionID > 2 && r.RegionDescription.Contains("ern") select r).ToList();
asked by Arian
Expression to string
How can I get a string like...Namespace.IMyService.Do("1") ...from the expression as demoed in this snip it:...IMyService myService = ...; int param1 = 1; myExpressionService.Get(c => myService.Do(param1)); ...I actually don't want to call ...Do... unles...
asked by Daniel A. White
EntityFramework query manipulation, db provider wrapping, db expression trees
I'm trying to implement data localization logic for Entity Framework. So that if for example a query selects ...Title... property, behind the scenes it should reference the column ...Title_enGB... or ...Title_deCH... depending on the current user culture ...
asked by benwasd
How to get the type of a property used within a generic expression?
public static void Map<T>(Expression<Func<T, object >> expression) { var memberExpression = (expression.Body as UnaryExpression).Operand as MemberExpression; var name = memberExpression.Member.Name; } ...Usage:...Map<Article>(x => x.Name) ...Name....
asked by Rookian
Expression of type 'System.DateTime' cannot be used for return type 'System.Object'
I've created an expression that I'm using for sorting which works fine, until I hit a ...DateTime... field, where I get the following error (on the second line):...Expression of type 'System.DateTime' cannot be used for return type 'System.Object'...Her...
asked by Wildcat
wcf Expression<T> parameter
I am trying to do something similar to using a lambda query inside a WCF operation parameter. I know there is no way to achieve this as lambda expressions are run-time and they can not be used in this way, but I think there are some solutions for this. My...
asked by Rati_Ge
Create expression from string (null reference)
Here is the problem:...We use table object to allow the users to perform some functionality like search, sort, pagination etc. Those tables works great. But there is a problem with one of the functionality : The sort (=OrderBy)....In fact, to allow the so...
asked by Whoami
Use string.Compare(a, b) in Expression
I've been teaching myself ...Expression Trees... since yesterday and I'm having problems comparing two string values. I've made this test case that fails with the error:...No method 'Compare' on type 'System.String' is compatible with the supplied argume...
asked by Chuck Savage
Creating MemberAcces with ExpressionTree to a complex type
I'd like to dynamically create a MemberAcess Expression to a deeper level then 1 (recursively):...public class Job { public string Name { get; set; } public int Salary { get; set; } } public class Employee { public string Name { get; set; } ...
asked by Adam Tal
Expression tree for a member access of depth > 1
public class Job { public string Name { get; set; } public int Salary { get; set; } } public class Employee { public string Name { get; set; } public Job Job { get; set; } } ...If I want to create an expression tree of a member access to E...
asked by Adam Tal
How can I Create a Expression.Property of a child object
normally I create an expresion in this way....ParameterExpression pe = Expression.Parameter(typeof(object1), "x"); string Name = "property1"; MemberExpression left = Expression.Property(pe, (object1).GetProperty(Name)); ...it produces ...left = x => x.p...
asked by Diana G
Generic method to calculate Euclidean Distance using expressions
I'd like a method that can calculate the Euclidean distance using expressions and order an IQueryable:...sqrt[(q1 - p1)^2 + (q2 - p2)^2 + ... + (qn - pn)^2]...This is the method signature I've come up with:...public static IOrderedQueryable<T> EuclideanDi...
asked by cofiem
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
Create array of all ExpressionTree/Func-parameters
Output of the following program is:...First: System.String. Second: System.String....The expected result is: First: hello1. Second: hello2....If i hardcode the index to 1 or 2 in Expression.Assign(resultArrayAccessor, parameters[0]) it works, but i need ...
asked by Lars Stenberg
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