Click here to Skip to main content
Click here to Skip to main content

Dynamically evaluating a JOIN expression with Linq

, 21 Feb 2010
Rate this:
Please Sign up or sign in to vote.
For the last little while I've been toying around with System.Linq.Expressions and a mini SQL parser to see how far I can go with evaluating plain text SQL expressions against arbitrary collections of objects.

Introduction

For the last little while, I've been toying around with System.Linq.Expressions and a mini SQL parser to see how far I can go with evaluating plain text SQL expressions against arbitrary collections of objects. It's mostly a side project for my own enjoyment but eventually I am hoping it actually turns into something broadly useful.

Results so far I've put on CodeProject:

It's been a while but today I opened up that code again and got a basic JOIN operator working. This is cool because ultimately I'd like to be able to join loosely related datasources; say across the mp3 tags in my music collection and the data on my last.fm account.

So just now I've been able to get this unit test to pass:

[TestMethod]
public void SimpleJoin()
{
    IEnumerable source<Person> = TestData.GetPeople();
    IEnumerable families<Family> = TestData.GetFamilies();

    var answer = source.Join(families, p => p.Address, f => f.Address,
        (p, f) => new FamilyMember 
	{ Name = p.Name, LastName = f.Name, Location = f.Address });

    var result = source.Query<Person, Family, FamilyMember>
              ("SELECT Name, that.Name AS LastName, Address AS Location 
              FROM this INNER JOIN that ON this.Address = that.Address", families);

    Assert.IsTrue(result.SequenceEqual(answer));
}

This is cool because now I can start generating complex queries without having compile time knowledge of the underlying data structures. Once I get things fleshed out further, I'll update things on CodeProject.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Don Kackman
Team Leader Starkey Laboratories
United States United States
The first computer program I ever wrote was in BASIC on a TRS-80 Model I and it looked something like:
10 PRINT "Don is cool"
20 GOTO 10
It only went downhill from there.
 
Hey look, I've got a blog

Comments and Discussions

 
QuestionWhere is the code source? Pinmemberelhumbertoz20-Sep-10 17:12 
AnswerRe: Where is the code source? PinmemberDon Kackman21-Sep-10 3:48 
I haven't yet posted updated code that includes JOINs. I have recently (just this week) gotten all of my unit tests to pass and will try to post an updated set of code sometime in the next week or two. It is significantly improved (I hope) from the previous versions; which were exploratory efforts.
 
I'll drop you a note when I get it posted.
10 PRINT "Software is hard. - D. Knuth"
20 GOTO 10

GeneralCase Pinmemberelhumbertoz20-Sep-10 16:41 
GeneralRe: Case PinmemberDon Kackman21-Sep-10 3:50 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

| Advertise | Privacy | Mobile
Web04 | 2.8.140721.1 | Last Updated 21 Feb 2010
Article Copyright 2010 by Don Kackman
Everything else Copyright © CodeProject, 1999-2014
Terms of Service
Layout: fixed | fluid