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Questions tagged [expression-trees]

Expression Trees are an abstract representation of code in a tree structure where each node of the tree represents a programming construct (conditional, assignment, method call, etc.)

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ExpressionTrees: getting a property name and its value

First I'll describe what I'm trying to achieve. I want to create a method that grabs a property name and its value for logging purposes, so I have this: public void Log(Expression> property,…
Evgeni
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Expression trees for code which doesn't type check

Is it possible to construct an expression tree in .NET 3.5 from code like Expression expr = () => (true + new object()) ? It seems to be impossible, since "A compiler-generated expression tree is always rooted in a node of type Expression", but I…
Alexey Romanov
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LINQ to Entities : "select new" expression tree throws System.NotSupportedException

I'm trying to build an Expression Tree that reflects a "select new" query. I'm using Ethan's answer to this question. It works great for common lists but with LINQ to Entities I get this exception: System.NotSupportedException: Unable to create a…
andres.chort
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how to convert parameterless constructor to MemberInitExpression

Can I create a MemberInitExpression or any expression of a parameterless constructor from a function that literally returns a parameterless constructor? public IQueryable GetViewSelect(IQueryable myQ) { return…
sickdoctor
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Negating a method call in an Expression tree

I'm generating a c# Linq expression dynamically as below, which will (in the example below) run string.Contains against the collection values. var dynamicMethod = "Contains"; var parameter = Expression.Parameter(typeof (MyClass), "type"); var…
LJW
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Using varying values in expressions in Entity Framework

This question was a inspired by the question: "Including a Method class inside an Expression". This question is not just "how can I find a solution to this" as that question already has that answer. My question is "How do I write a Expression that…
Scott Chamberlain
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Is it possible to build and incrementally evaluate/mutate expression trees in Boost.Proto?

Is it possible to extract parts of a Boost.Proto expression tree, evaluate them individually (externally), and then mutate the expression tree, replacing the extracted parts with a result? In my specific case, I'm trying to evaluate if I could…
meastp
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How do you hold a reference to a NewExpression?

I have this code: public static Func CreateBinder() { NewExpression dataTransferObject = Expression.New(typeof(T).GetConstructor(Type.EmptyTypes)); ParameterExpression dataReader =…
sircodesalot
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nHibernate HqlTreeBuilder to implement Linq methods for HierarchyId

I am looking at implementing a Hierarchy data structure in SQL Server using HierarchyId, and I need to add extension methods that can be used, via Linq, to use the HierarchyId methods exposed in TSQL. Now I have all the code for connecting a Linq…
Nick Albrecht
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expression tree to source code conversion

Is there a library which converts arbitrary c# expression trees to string (representing C# source which would build up that expression tree) var expTree = ...; var stringRepresentation = Library.ToCSharpSource(expTree); // <- something like…
D.R.
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Best way to determine if an expression is a constant expression

Which one do you prefer for testing if an expression is a ConstantExpression? From the NodeType property or a cast, and why? public static bool IsConstantExpression(Expression expression) { return expression.NodeType ==…
Toto
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Need help building LINQ to SQL Expression

I need to translate the following Code to an Expression and I will explain why: results = results.Where(answer => answer.Question.Wording.Contains(term)); results is IQueryable Question is ISurveyQuestion Wording is String The…
Joe Flateau
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Create a reusable "meta-predicate" function accepting lambda operand parameters

Is it possible to create a "meta-predicate" by writing a a function that takes 2 (or 4 if necessary) lambdas which represent the left and right side properties (operands) and have it generate an predicate. Something like the following code…
j0tt
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Lambda Generic Expression w/ Out Parameter

I am trying to use expressions w/ lambda delegates to obtain the name of the calling method but it is not formatting it properly. Here is what I have so far: Question is.. how do I get what I am to expect similar to foo.Method.Name for both lambda…
Latency
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Expression Tree and Compile method

This is all about the Compile method of Expression Type. Sorry being naïve since I am a late comer. I have been reading about building expression in order to enables dynamic modification of executable code. And It make sense for me when it comes to…
S.N
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