Expression Tree Tutorial - Knowledge Base (KB)
115 results in tag: .net
In C#, how can I represent 'String.Contains("term")' with an expression tree?
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
Within a generic extension method, how do I apply OrderBy to an IQueryable using a string column name?
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
I'm not sure how to make an expression tree using IEnumerableTSource>. 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
In C#, how can I build an Expression Tree by parsing XML?
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
What is the best way to integrate 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
Dummies' expression trees?
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
Linq to SQL query compilation 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 may the type of a parameter in an expression be changed?
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 a simple method to convert a string (lambda expression) 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 do you break down an equation into separate variable formulas?
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
How can I parse random strings into expression trees in C#?
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-
What is a decent use case for Expression Trees in.net 4.0?
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
Trees of expressions/statements
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 is the purpose of Expression.Reduce()?
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..
Invoking a Delegate and Expression Trees
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 a new expression from an existing one
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
An argument exception occurs while using an Expression Tree with Property Inheritance.
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 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
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
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