What are Expression Trees, how do you use them, and why would you use them?

c# .net linq expression-trees
Donny picture Donny · Apr 4, 2012 · Viewed 37.4k times · Source

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 of use.

Answer

Roy Dictus picture Roy Dictus · Apr 4, 2012

An Expression Tree is a data structure that contains Expressions, which is basically code. So it is a tree structure that represents a calculation you may make in code. These pieces of code can then be executed by "running" the expression tree over a set of data.

A great thing about expression trees is that you can build them up in code; that is, you build executable code (or a sequence of steps) in code. You can also modify the code before you execute it by replacing expressions by other expressions.

An Expression is then a function delegate, such as (int x => return x * x).

See also http://blogs.msdn.com/b/charlie/archive/2008/01/31/expression-tree-basics.aspx

Related questions

How do I apply OrderBy on an IQueryable using a string column name within a generic extension method?

public static IQueryable<TResult> ApplySortFilter<T, TResult>(this IQueryable<T> query, string columnName) where T : EntityObject { var param = Expression.Parameter(typeof(T), "o"); var body = Expression.PropertyOrField(param,columnName); var sortExpression = Expression.Lambda(body, …

Read More
How does PredicateBuilder work

C# in a Nutshell has a free class called PredicateBuilder which constructs LINQ predicates piece by piece available here. Here's an extract of the method which adds a new expression to the predicate. Could someone explain it? (I have seen …

Read More
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 …

Read More