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.netexpression-trees
Aamol
Aamol

Reputation: 1199

What is the benefit of Expression Trees?

While developing the applications using .Net language, I am not getting the use or benefit of the expression tree? Is it really necessary ?

Upvotes: 5

Views: 4462

Answers (5)

Muhammad Sulaiman
Muhammad Sulaiman

Reputation: 2615

The idea behind Expression tree is to Put your code in well-defined data structure (i.e. tree), so other frameworks can analyze it, parse it and run it on its behalf..

For Example: you would not write a select from where SQL-Query in C#, but you can wrap your C# code with an expression tree and later the converter will convert it to its according SQL code.

Upvotes: 0

Marc Gravell
Marc Gravell

Reputation: 1062660

An expression tree allows you to express your code in regular C#, but to deconstruct that, inspect it, and interpret it. For example, you might interpret it by writing an equivalent TSQL string (example: LINQ-to-SQL or Entity Framework), or a web-service query (astoria). You might interpret it as an RPC call (I've written an expression-based RPC layer).

To repeat my "Explaining Expression" blog entry:

  • The delegate version (Func<int,int,bool>) is the beligerant manager; "I need you to give me a way to get from 2 integers to a bool; I don't care how - when I'm ready, I'll ask you - and you can tell me the answer".
  • The expression version (Expr<Func<int,int,bool>>) is the dutiful analyst; "I need you to explain to me - if I gave you 2 integers, how would you go about giving me a bool?"

If you have the expression, you can either call Compile() to form a delegate (to do it exactly as explained), or you can unpick it and do something similar based on what steps they took.

Another view on Expression is that it can act as a simplified version of ILGenerator - but still be pretty versatile. Very useful for meta-programming. Here's an article exploring that approach.

Upvotes: 6

Snowbear
Snowbear

Reputation: 17274

If you do not get benefits of the expression trees then I think:
- either you do not have any code which requires expression trees
- or you do not see places where your code can be improved by using expression trees.

First point is Ok, most of the applications I've developed had no place for expression trees. And in order to deal with second point you just have to know what are the expression trees, how do they work and what they can/cannot do.

Expression trees are usually used when you need to have an ability to traverse some code model, for example in order to generate some other code based on this one. As already mentioned this approach is used in Linq-to-SQL for example. Another not out-of-box example might be an application where you need to have an object's property as a first class citizen object in your application, i.e. you need to be able to pass the property as an instance of some class. The same can be done with reflection but expression trees allow making such code less stringly typed.

Upvotes: 1

Richard
Richard

Reputation: 108975

Expression trees are using widely in LINQ to SQL, Entity Framework, ASP.NET MVC's HTML extensions where the runtime needs to interpret the expression in a different way (LINQ to SQL and EF: to create SQL, MVC: to determine the selected property or field).

If you don't need that can of re-interpretation of a C#/VB expression you don't need to use Expression trees.

(There are plenty of things in .NET you'll not use most of the time: eg. ServiceBase only applies if writing a service, WPF is not relevant to a web app.)

Upvotes: 1

Darin Dimitrov
Darin Dimitrov

Reputation: 1038730

Expression trees allow you to build code dynamically at runtime instead of statically typing it in the IDE and using a compiler. They are well explained in the documentation.

Upvotes: 2

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