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.)
Questions tagged [expression-trees]
2090 questions
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C# switch in lambda expression
Is it possible to have a switch in a lambda expression? If not, why? Resharper displays it as an error.
Toto
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4 answers
.NET: Accessing non-public members from a dynamic assembly
I'm working on a library that allows users to input arbitrary expressions. My library then compiles those expressions as part of a larger expression into a delegate. Now, for still unknown reasons compiling the expression with Compile…
JulianR
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4 answers
Why are expression trees safer than reflection?
In this answer to the question of the fastest way to determine if a property contains a given attribute, user Darin Dimitrov posited that expression trees are safer than reflection. Is this true, and if so, why is it true?
Charles Y.
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Calling a Generic Method using Lambda Expressions (and a Type only known at runtime)
You can use Lambda Expression Objects to represent a lambda as an expression.
How do you create a Lambda Expression Object representing a generic method call, if you only know the type -that you use for the generic method signature- at runtime?
For…
SDReyes
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Can I generate an async method dynamically using System.Linq.Expressions?
I know the compiler can't convert an async lambda expression to an expression tree, but is it possible to generate the expression tree manually ?
var expr = Expression.Lambda>(
// how do I use 'await' in the body here?
);
var func =…
Thomas Levesque
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C#: An item with the same key has already been added, when compiling expression
Ok, here's a tricky one. Hopefully there is an expression guru here who can spot what I am doing wrong here, cause I am just not getting it.
I am building up expressions that I use to filter queries. To ease that process I have a couple of…
Svish
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5 answers
Efficiently eliminate common sub-expressions in .NET Expression Tree
I've written a DSL and a compiler that generates a .NET expression tree from it.
All expressions within the tree are side-effect-free and the expression is guaranteed to be a "non-statement" expression (no locals, loops, blocks etc.). (Edit: The…
Ani
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Get the parameter value from a Linq Expression
I have the following class
public class MyClass
{
public bool Delete(Product product)
{
// some code.
}
}
Now I have a helper class that looks like this
public class Helper
{
public Type Type;
public string…
Jürgen Steinblock
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How to create a Expression.Lambda when a type is not known until runtime?
This is best explained using code. I have a generic class that has a method that returns an integer. Here is a simple version for the purposes of explaining...
public class Gen
{
public int DoSomething(T instance)
{
// Real code…
Phil Wright
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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,…
Michiel van Oosterhout
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4 answers
Parsing and Translating Java 8 lambda expressions
In C# you can enclose a lambda expression in an expression tree object and then possibly parse it. I was wondering if this is also possible in Java?
What I'm looking for is doing something like this:
BooksRepository.getAll()
.where(b -> b.getIban()…
Eyad
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How do I rewrite query expressions to replace enumerations with ints?
Inspired by a desire to be able to use enumerations in EF queries, I'm considering adding an ExpressionVisitor to my repositories that will take incoming criteria/specifications criteria and rewrite them to use the corresponding persisted int…
Morten Mertner
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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…
KevinDeus
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Expression.Bind() - what does it actually do?
So I've been playing with dynamically building expression trees lately and came across this method, which seems kinda odd. At first I thought "oh cool this is exactly what I need" after constantly writing code along the lines of
var left = member…
Ilia G
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Convert LINQ Expression to SQL Text without DB Context
Either LINQ to SQL or LINQ to Entities already have the ability to convert LINQ into a SQL text string. But I want my application to make the conversion without using the db context - which in turn means an active database connection - that both…
Brent Arias
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