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]
1973 questions
1021
votes
10 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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542
votes
22 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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125
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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100
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
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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94
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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88
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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83
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
70
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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70
votes
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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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…
Donny
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67
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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61
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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56
votes
3 answers
What is the best resource for learning C# expression trees in depth?
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…
Charlie Flowers
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