Expression Tree Tutorial - Knowledge Base (KB)
207 results in tag: lambda
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
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
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
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
Is it feasible to combine two queryables in C# using Linq2Sql?
I have one queryable... where I have used various ...Where... and ...WhereBetween... statements to narrow the collection down to a certain set. Now ...I need to add kind of a ...Where || WhereBetween.... In other words, I can't just chain them together li...
asked by Svish
How do I change an ExpressionFuncSomeType>> to an ExpressionFuncOtherType>> in C#?
I have used C# expressions before based on lamdas, but I have no experience composing them by hand. Given an ...Expression<Func<SomeType, bool>> originalPredicate..., I want to create an ...Expression<Func<OtherType, bool>> translatedPredicate.......In th...
asked by Michiel van Oosterhout
Property name retrieved from lambda expression
Is there a better way to get the Property name when passed in via a lambda expression? Here is what i currently have....eg. ...GetSortingInfo<User>(u => u.UserId); ...It worked by casting it as a memberexpression only when the property was a string. beca...
asked by Schotime
What is the best way to study C# expression trees thoroughly?
When I first typed this question, I did so in order to find the duplicate questions, feeling sure that someone must have already asked this question. My plan was to follow those dupe links instead of posting this question. But this question has not been a...
asked by Charlie Flowers
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
Why would you want to use ExpressionFuncT>> instead of FuncT>?
I understand lambdas and the ...Func... and ...Action... delegates. But expressions stump me. In what circumstances would you use an ...Expression<Func<T>>... rather than a plain old ...Func<T>...?
asked by Richard Nagle
How can I build an ExpressionFuncMyClass, bool>> predicate dynamically?
How would I go about using an Expression Tree to dynamically create a predicate that looks something like......(p.Length== 5) && (p.SomeOtherProperty == "hello") ...So that I can stick the predicate into a lambda expression like so......q.Where(myDynamic...
asked by Senkwe
Issues of Expression vs. Predicate
I've got a bit of a challenge where I have to create an expression tree to represent a query input by the user. Since I don't have the time to create all the possible cases of user input, I figured that expression trees would aid me in solving this....For...
asked by J. Steen
How do linq expression trees acquire the value of a parameter?
AddOptional<tblObject>(x =>x.Title, objectToSend.SupplementaryData); private static void AddOptional<TType>(Expression<Func<TType,string>> expr, Dictionary<string, string> dictionary) { string propertyName; string propertyValue; Expression e...
asked by Tadeusz Wójcik
Conversion from Lambda to Expression Tree
I will keep it really simple,...How do I get expression tree out of lambda??...or from query expression ?
asked by Prashant Cholachagudda
In a LINQ expression tree, how do you evaluate a solitary boolean expression?
I'm using the standard visitor pattern to iterate through a LINQ expression tree in order to generate dynamic SQL WHERE clauses....My issue is that unlike C#, you can't use a standalone boolean expression in SQL; you have to compare it to either 1 or 0...
asked by Nathan Ridley
C# lambda expression switch
Is it possible to have a switch in a lambda expression? If not, why? Resharper displays it as an error.
asked by Toto
Expression Tree with iQueryable
Can anybody explain me how to use (1) iQueryable (2) Expression Tree in C# by providing a very basic example? Both are not correlated, instead of making two separate questions, I wish to clear my doubt in a single question....Advanced Thanks.
asked by user184805
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