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
1136
votes
12 answers
Why would you use Expression> rather than Func?
I understand lambdas and the Func and Action delegates. But expressions
stump me.
In what circumstances would you use an Expression> rather than a plain old Func?
Richard Nagle
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593
votes
23 answers
Retrieving Property name 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(u => u.UserId);
It worked by casting it as a memberexpression only when the property was a string.…
Schotime
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127
votes
1 answer
Are Roslyn SyntaxNodes reused?
I've been taking a look to Roslyn CTP and, while it solves a similar problem to the Expression tree API, both are immutable but Roslyn does so in a quite different way:
Expression nodes have no reference to the parent node, are modified using a…
Olmo
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105
votes
4 answers
LINQ to Entities only supports casting EDM primitive or enumeration types with IEntity interface
I have the following generic extension method:
public static T GetById(this IQueryable collection, Guid id)
where T : IEntity
{
Expression> predicate = e => e.Id == id;
T entity;
// Allow reporting more…
Steven
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103
votes
5 answers
What does Expression.Quote() do that Expression.Constant() can’t already do?
Note: I am aware of the earlier question “What is the purpose of LINQ's Expression.Quote method?”, but if you read on you will see that it doesn’t answer my question.
I understand what the stated purpose of Expression.Quote() is. However,…
Timwi
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97
votes
7 answers
Serializing and Deserializing Expression Trees in C#
Is there a way to Deserialize Expressions in C#, I would like to store Expressions in a Database and load them at run time.
Alexandre Brisebois
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91
votes
4 answers
Compiled C# Lambda Expressions Performance
Consider the following simple manipulation over a collection:
static List x = new List() { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
var result = x.Where(i => i % 2 == 0).Where(i => i > 5);
Now let's use Expressions. The following code is roughly…
Hugo Sereno Ferreira
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91
votes
8 answers
How do I apply OrderBy on an IQueryable using a string column name within a generic extension method?
public static IQueryable ApplySortFilter(this IQueryable query, string columnName)
where T : EntityObject
{
var param = Expression.Parameter(typeof(T), "o");
var body = Expression.PropertyOrField(param,columnName);
…
JTew
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84
votes
7 answers
Expression trees for dummies?
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.
Dave
74
votes
6 answers
What's the purpose of the Expression class?
I'm wondering what exactly is the difference between wrapping a delegate inside Expression<> and not ?
I'm seeing Expression being used a lot with LinQ, but so far I've not found any article that explains the difference between this, and just…
Steffen
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74
votes
4 answers
How do I create an expression tree to represent 'String.Contains("term")' in C#?
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
flesh
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74
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9 answers
Access the value of a member expression
If i have a product.
var p = new Product { Price = 30 };
and i have the following linq query.
var q = repo.Products().Where(x=>x.Price == p.Price).ToList()
In an IQueryable provider, I get a MemberExpression back for the p.Price which contains a…
Schotime
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71
votes
7 answers
Practical 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?
Dmitri Nesteruk
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69
votes
1 answer
What are Expression Trees, how do you use them, and why would you use them?
I just came across the concept of expression trees which I have heard multiple times. I just want to understand what is meant by an expression tree and its purpose.
I would love it if someone could also direct me to simple explanations and samples…
Donald N. Mafa
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67
votes
1 answer
PropertyExpression is missing
I try to write a simple example using Expressions, but have a strange bug: I can't use PropertyExpression at compile time. When I write it I get an error and it doesn't compile
But in runtime at breakpoint I can write
var runtimeBody =…
Alex Zhukovskiy
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