Expression Tree Tutorial - Knowledge Base (KB)
115 results in tag: .net
How do I create an expression tree to represent 'String.Contains("term")' in C#?
I am just getting started with expression trees so I hope this makes sense. I am trying to create an expression tree to represent:...t => t.SomeProperty.Contains("stringValue"); ...So far I have got:... private static Expression.Lambda<Func<string, boo...
asked by flesh
How do I apply OrderBy on an IQueryable using a string column name within a generic extension method?
public static IQueryable<TResult> ApplySortFilter<T, TResult>(this IQueryable<T> query, string columnName) where T : EntityObject { var param = Expression.Parameter(typeof(T), "o"); var body = Expression.PropertyOrField(param,columnName); var sor...
asked by JTew
How do I create an expression tree calling IEnumerable<TSource>.Any(...)?
I am trying to create an expression tree that represents the following:...myObject.childObjectCollection.Any(i => i.Name == "name"); ...Shortened for clarity, I have the following:...//'myObject.childObjectCollection' is represented here by 'propertyExp' ...
asked by flesh
How do I Create an Expression Tree by Parsing Xml in C#?
I am looking to create an expression tree by parsing xml using C#. The xml would be like the following:...<Expression> <If> <Condition> <GreaterThan> <X> <Y> </GreaterThan> </Condition> <Expression /> <If> <Else> <Expression />...
asked by SharePoint Newbie
How do I combine two Member Expression Trees?
I'm trying to combine the following expressions into a single expression: item => item.sub, sub => sub.key to become item => item.sub.key. I need to do this so I can create an OrderBy method which takes the item selector separately to the key selector. Th...
asked by LaserJesus
Expression trees for dummies?
I am the dummy in this scenario....I've tried to read on Google what these are but I just don't get it. Can someone give me a simple explanation of what they are and why they're useful?...edit: I'm talking about the LINQ feature in .Net.
asked by Dave
Compiling Linq to SQL queries from a non-trivial IQueryable
Is there a way to use the CompiledQuery.Compile method to compile the Expression associated with an IQueryable? Currently I have an IQueryable with a very large Expression tree behind it. The IQueryable was built up using several methods which each supply...
asked by LaserJesus
how to change the type of the parameter in an Expression?
since i am using POCOS in my domain, i want my repository to be able to received Expression filters of the type of my POCOS and change the parameter in the expression to be the of type of my LINQ tables, my fields have the same name as my members so i was...
asked by Oscar Cabrero
Is there an easy way to parse a (lambda expression) string into an Action delegate?
I have a method that alters an "Account" object based on the action delegate passed into it:...public static void AlterAccount(string AccountID, Action<Account> AccountAction) { Account someAccount = accountRepository.GetAccount(AccountID); AccountAct...
asked by Whisk
How to convert an equation into formulas for individual variables?
How to convert an equation into formulas for individual variables? I am thinking about a math equations like:...c^2 = a^2 + b^2 ...I would like to have a function that could process any formula, and give me the individual variable formulas. The above equ...
asked by Bobby Ortiz
C#: How to parse arbitrary strings into expression trees?
In a project that I'm working on I have to work with a rather weird data source. I can give it a "query" and it will return me a DataTable. But the query is not a traditional string. It's more like... a set of method calls that define the criteria that I ...
asked by Vilx-
Whats a good use case for .net 4.0 Expression Trees?
This one was inspired by my language-guru co-worker who can't seem to find a good use for them, and after a few lame attempts of my own, I'd have to agree. ...Now I know these concepts tend to flow a lot more easily once you get some good practical reason...
asked by KevinDeus
Expression/Statement trees
Updated Question Further Down...I've been experimenting with expression trees in .NET 4 to generate code at runtime and I've been trying to implement the ...foreach... statement by building an expression tree. ...In the end, the expression should be able ...
asked by JulianR
What does Expression.Reduce() do?
I've been working with expression trees for a few days now and I'm curious to know what Expression.Reduce() does. The ...msdn documentation... is not very helpful as it only states that it "reduces" the expression. Just in case, I tried an example (see be...
asked by d..
Expression Trees and Invoking a Delegate
So I have a ...delegate... which points to some function which I don't actually know about when I first create the ...delegate... object. The object is set to some function later....I also then want to make an expression tree that invokes the delegate wit...
asked by PythonPower
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
Expression Tree with Property Inheritance causes an argument exception
Following this post: ...link text... I'm trying to create an expression tree that references the property of a property. My code looks like this:...public interface IFoo { void X {get;set;} } public interface IBar : IFoo { void Y {get;set;} } pu...
asked by Adam Driscoll
What are some examples of MemberBinding LINQ expressions?
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
Building a LINQ expression tree: how to get variable in scope
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
Why do I get a null reference exception in this expression tree?
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
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