Expression Tree Tutorial - Knowledge Base (KB)
656 results
The value of a member expression may be accessed.
If i have a product....var p = new Product { Price = 30 }; ...and i have the following linq query....var q = repo.Products().Where(x=>x.Price == p.Price).ToList() ...In an IQueryable provider, I get a MemberExpression back for the p.Price which contains a...
asked by Schotime
NotifyProperty (typesafe) Using linq expressions, it was changed.
Form ...Build your own MVVM... I have the following code that lets us have typesafe NotifyOfPropertyChange calls:...public void NotifyOfPropertyChange<TProperty>(Expression<Func<TProperty>> property) { var lambda = (LambdaExpression)property; Memb...
asked by bitbonk
In the Select() query, a lambda expression will be utilized.
I am trying to build a lambda expression, containing two assignments (as shown further down), that I can then pass to a Queryable.Select() method. ...I am trying to pass a string variable into a method and then use that variable to build up the lambda exp...
asked by jameschinnock
Changing a predicate's expression tree to target a different type
Intro...In the application I 'm currently working on, there are two kinds of each business object: the "ActiveRecord" kind and the "DataContract" kind. So for example, there would be:...namespace ActiveRecord { class Widget { public int Id { g...
asked by Jon
With the expression argument, call the asp.net mvc Html Helper from inside a custom html helper.
I am trying to write an html helper extension within the asp.net mvc framework....public static MvcHtmlString PlatformNumericTextBoxFor<TModel>(this HtmlHelper instance, TModel model, Expression<Func<TModel,double>> selector) where TModel : TableS...
asked by Frank Michael Kraft
expression tree to sql statement
I'm wondering how one would translate a sql string to an expression tree. Currently, in Linq to SQL, the expression tree is translated to a sql statement. How does on go the other way? How would you translate ...select * from books where bookname like ...
asked by Joo Park
Using Lambda Expressions to Call a Generic Method (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
What are some LINQ expressions that use MemberBinding?
There are three possibilities, but I can't find examples:...System.Linq.Expressions.MemberAssignment...System.Linq.Expressions.MemberListBinding...System.Linq.Expressions.MemberMemberBinding...I want to write some unit tests to see if I can handle them, b...
asked by Michiel van Oosterhout
expressive tree-based dynamic query
I have a form in which the user will choose the following from dropdown lists:... table_name columnName_to_sort_by columnName_to_search_in ...The user shall enter ...Search_text... in a text box...The form shall draw data from many tables. I want to ...
asked by user375492
What is the purpose of ExpressionVisitor.VisitT>?
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...
asked by Jeff
How to evaluate a prefix notation expression
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
asked by ad126
Expression trees vs. CodeDom in C# 4.0
What are the differences between Expression trees and CodeDom? Which should I use for which scenario?
asked by Yaron Naveh
Creating a method-calling expression tree
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 parame...
asked by brianberns
How to obtain variables in scope while creating a LINQ expression tree
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() { ...
asked by Sandor Drieënhuizen
In this expression tree, why am I getting a null reference exception?
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(MyTyp...
asked by Sandor Drieënhuizen
Local Evaluation of Linq Func/Expression
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)); ...
asked by Shlomo
Create a completely dynamic where clause using an expression tree and run it via IQueryable.
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...
asked by Wouter Vegter
Using an Expression Tree to Combine Expressions
How can I build an expression tree when parts of the expression are passed as arguments?...E.g. what if I wanted to create expression trees like these:...IQueryable<LxUser> test1(IQueryable<LxUser> query, string foo, string bar) { query=query.Where(x =>...
asked by laktak
LINQ Querying an Entity with Dynamic Field Names
I have created a dynamic search screen in ASP.NET MVC. I retrieved the field names from the entity through reflection so that I could allow the user to choose which fields they wanted to search on instead of displaying all fields in the view....When the ...
asked by Scott Lance
In C#, use reflection to convert a function to a predicate.
I'm basically trying to do ...this..., but I don't know what T will be, so I'm building things up using Reflection and Expression trees....// Input (I don't know about "Book") Type itemType = typeof(Book); // Actual Code // Build up func p => p.AuthorNam...
asked by Jon Smock
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