Expression Tree Tutorial - Knowledge Base (KB)
557 results in tag: c#
Using a Linq Expression tree, find an event.
The compiler usually chokes when an event doesn't appear beside a ...+=... or a ...-=..., so I'm not sure if this is possible....I want to be able to identify an event by using an Expression tree, so I can create an event watcher for a test. The syntax wo...
asked by user1228
Without distinct try-catch blocks, try-catch every line of code.
I do not currently have this issue..., but you never know, and thought experiments are always fun....Ignoring the obvious problems that you would have to have with your architecture to even be attempting this..., let's assume that you had some horribly-wr...
asked by tags2k
C# Expression Trees Advice
I'm working on a method that accepts an expression tree as a parameter, along with a type (or instance) of a class....The basic idea is that this method will add certain things to a collection that will be used for validation....public interface ITestInte...
asked by Ian P
Expression Trees in C#: Serializing and Deserializing
Is there a way to Deserialize Expressions in C#, I would like to store Expressions in a Database and load them at run time.
asked by Alexandre Brisebois
What is the best way to create a Linq Expression Tree that compares to a generic object?
I have an IQueryable and an object of type T....I want to do IQueryable().Where(o => o.GetProperty(fieldName) == objectOfTypeT.GetProperty(fieldName))...so ......public IQueryable<T> DoWork<T>(string fieldName) where T : EntityObject { ... T...
asked by JTew
Parsing of Lambda Expression Trees
I am trying to use Lambda Expressions in a project to map to a third party query API. So, I'm parsing the Expression tree by hand....If I pass in a lambda expression like:...p => p.Title == "title" ...everything works....However, if my lambda expression l...
asked by Keith Fitzgerald
How can I retrieve the field value for a type ExpressionType.MemberAccess?
I am parsing an Expression Tree. Given a NodeType of ExpressionType.MemberAccess, how do I get the value of that Field? ...From C# MSDN docs: MemberAccess is A node that represents reading from a field or property. ...A code snippet would be incredibly, ...
asked by Keith Fitzgerald
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
In a C# Expression tree, how can I set a field value?
Given:...FieldInfo field = <some valid string field on type T>; ParameterExpression targetExp = Expression.Parameter(typeof(T), "target"); ParameterExpression valueExp = Expression.Parameter(typeof(string), "value"); ...How do I compile a lambda expressio...
asked by TheSoftwareJedi
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
In Expression Trees, what is the best technique to invoke an instance method?
What is the best way to call an instance method within an Expression Tree? My current solution is something like this for an interface method "object GetRowValue(rowIndex)" of the interface IColumn....public static Expression CreateGetRowValueExpression( ...
asked by Rauhotz
The use of expression trees
Expression trees are a nice feature, but what are its practical uses? Can they be used for some sort of code generation or metaprogramming or some such?
asked by Dmitri Nesteruk
Expression. Alternatively, the argument 'item' is out of 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
How do you feed bits of a LINQ query into a function in LINQ to SQL?
Is it possible to pass parts of a linq Query into a function? I want create a common interface for my DAL that always uses the same query interface. For example, ...List<T> Get(Join j, Where w, Select s){ return currentDataContext<T>.Join(j).Wh...
asked by Arron S
Where Predicate Type Arguments in C#
I have an XElement with values for mock data. ...I have an expression to query the xml:...Expression<Func<XElement, bool>> simpleXmlFunction = b => int.Parse(b.Element("FooId").Value) == 12; ...used in:...var simpleXml = xml.Elements("Foo").Where(si...
asked by blu
how to make a deep property expression tree / lambda from a string
Given a string: "Person.Address.Postcode" I want to be able to get/set this postcode property on an instance of Person. How can I do this? My idea was to split the string by "." and then iterate over the parts, looking for the property on the previous typ...
asked by Andrew Bullock
Parent Navigation Property C# Expression Tree Parameter
How can I create a ParameterExpression for the parent side of a 1 to * Navigation Property?...The following works for the child entity:...var parameter = Expression.Parameter( typeof(T), // where T is the entity type GetParameterName()); // helper...
asked by blu
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
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