Road to Dynamic LINQ – Part 2

Vedran Maršić AKA Fosna

Warning: Expression Trees Ahead

About me Vedran Maršić AKA Fosna

dev at http://www.axilis.com/author/vmarsic/

organizing programming workshops for kids Logo, Scratch, HTML, CSS, JavaScript, Python, C++

We’ll cover Part 1

What is expression tree in C# How is it different from similar looking lambda delegates How to build expression trees How to parse expression trees Where are you already using them

Part 2 Check out few expression tree exploits Point to brilliant, not easy to understand, ideas or projects from some cool

developer maniacs

We won’t cover Implementing LINQ providers Implementing deep copy Implementing faster static dictionary Implementing IoC container

Need for Dynamic Queries

Applied Expression TreesC# 6.0 Taste Before C# 6.0

Sort by Custom Property... in LINQ to Entity Framework

Try to support sort by each column in grid on web page Chances are grid will send to the server

a string for property name and a sort order

Dynamic Searching... in LINQ to Entity Framework Try to support search by each column in grid on web page

Chances are grid will send to the server a property name and a value to compare to

Let’s not bother with more complex requirements for brevity of the presentation

Get Property or Method NamesSomething like nameof operators in C# 6.0

Similar thing was possible with older compiler

Hint:

Get Over NULL Reference Exceptions Null-conditional operators in C# 6.0

Empty string if person is null or person.Child is null

Simmilar thing was possible with older compilerstring childName = person.Safely(x => x.Child.Name);

Source Code Available at

https://github.com/axilis/RoadToDynamicLinq

Some Other Ideas LINQ update, insert, delete statement with where clause

without dbContext.SaveChanges() magic Entity Framework Extended Library by Paul Welter of LoreSoft https://github.com/loresoft/EntityFramework.Extended

TypeSafe property changed http://

stackoverflow.com/questions/3551947/in-c-why-expression-trees-and-when-do-you-need-to-use-them/3551991#3551991

Lambda equality comparer with delegates

Stay Away from Other Ideas Deep copy Customizable convention based copy, like AutoMapper Fast IoC Container

BarbarianIOC : A simple IOC Container by Sacha Barber, 25 Feb 2013 http://www.codeproject.com/Articles/552514/BarbarianIOC-A-simple-IOC-Container

Faster static dictionary StaticStringDictionary - Fast Switching With LINQ Revisited, AUG 28TH, 2008, by Gustavo Guerra http://functionalflow.co.uk/blog/2008/08/28/staticstringdictionary-fast-switching-with-linq-revisited/

Your own LINQ provider Using Expression Trees in Your APIs by Patrick Steele04/01/2011 https://visualstudiomagazine.com/Articles/2011/04/01/pccsp_Expression-Trees.aspx

Thanks. Bye!No questions, right?

Resources Start with

http://stackoverflow.com/a/403233/953338 Expression Tree Basics, Charlie Calvert 31 Jan 2008 3:49 AM

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

Published by Olexander Ivanitskyi on Tuesday, June 11, 2013 LINQ: Func<T> vs. Expression<Func<T>> http://ivanitskyi.blogspot.hr/2013/06/linq-func-vs-expression.html

 asked Apr 27 '09 at 13:50, Richard Nagle Why would you use Expression<Func<T>> rather than Func<T>? http://

stackoverflow.com/questions/793571/why-would-you-use-expressionfunct-rather-than-funct

Resources Dynamic LINQ examples

https://www.nuget.org/packages/System.Linq.Dynamic/ C# 6.0 Features

https://github.com/dotnet/roslyn/wiki/New-Language-Features-in-C%23-6 Canonical Functions

https://msdn.microsoft.com/en-us/library/vstudio/bb738626(v=vs.100).aspx

The .NET Programmer’s Playground - LinqPad http://www.linqpad.net/