Aral Balkan: Historical Archive — Using mogenerator — Code generation for Core Data

Using mogenerator — Code generation for Core Data — in Xcode 3.1

Data model

Core Data manages all the grubby details of data persistence and abstracts away the actual data layer (whether it's SQL and its object-relational impedance mismatch baggage or XML and the joy of serialization/de-serialization/rinse/repeat) for you. Actually, it does much more than that, such as handling undo/redo.

One area that I've been finding Core Data somewhat lacking is in the tools support in XCode for code generation. You can generate code using the Design → Data Model → Copy… Method Declarations/Implementations to Clipboard options but it's a convoluted and manual process. This is an all-the-more interesting oversight because the Core Data modeling tool in XCode is otherwise rather excellent.

mogenerator to the rescue!

To address this niche, Jonathan 'Wolf' Rentzsch has a free command-line tool called mogenerator. You can read Jon's motivations for building the tool, but don't follow the project links in that post as they're 404. You can also read about Jon's updates to the app in versions 1.2 and 1.5.

The latest release build, according to the project's SourceForge download page appears to be version 1.6.1 (157KB, .DMG).

An error with XCode 3.1.x

In the version of XCode that I'm running (don't you love how NDAs make you sound cryptic and mysterious? No, I didn't think so!), running mogenerator resulted in the following error:

sh: /Developer/Library/Xcode/Plug-ins/XDCoreDataModel.xdplugin/Contents/Resources/momc: No such file or directory
/Users/wolf/code/sf/redshed/cocoa/mogenerator/mogenerator.m:259: failed assertion `model'

It appears that since the last release build of mogenerator, the location of the momc app has changed. It's easy enough to fix this with a symbolic link so I didn't resort to compiling the latest from trunk which may or may not have the fix for this already implemented (see the new Trac and SVN repositories for the project for the latest updates).

If you'd rather use the release version like I did, the symbolic link you have to create is below (just run the command below in Terminal):

ln -s /Developer/usr/bin/momc /Developer/Library/Xcode/Plug-ins/XDCoreDataModel.xdplugin/Contents/Resources/momc

The simplest way to learn the app is to read the help via mogenerator --help and a simple example of its syntax is below:

mogenerator -m MyAwesomeApp.xcdatamodel -O Classes

That will generate four files for each Entity in your data model in the specified Classes folder. If, for example, you have an entity called User, it will create _User.h and _User.m, which hold the generated code (that you shouldn't edit yourself) and files for a _User subclass called User.h and User.m that you can use to implement your custom logic.

Comments

Hello Aral ! We write May 2009 a.d. and I am already more than chock full of approaches to (web) app dev ... But nevertheless Your Xcode/Core Data/mogenerator approach is new to me ... I have the impression that this approach is MAC-based only; is that correct ? If yes, it is no wonder I have not stumbled upon this approach before, because I am exploring the approaches in the WINDOWS world. What I like about Core Data at first glance is its baked-in Undo/Redo Management :-) ! So yes: Can one use this Xcode/Core Data/mogenerator approach to build RUEs (Rich User Experiences) of all kinds ? For example to build browser-based RIAs, too ? And could this approach be worth to switch from the WINDOWS world to the MAC world ? Or asked the other way round: Do You have a recommendation for an approach in the WINDOWS world which resembles the Xcode/Core Data/mogenerator approach ? Cheers and Tschüss Kai (Tischler) from Northrhine-Westfalia in Germany
by Kai Tischler on 2009-05-03 17:36:30
[...] is a very useful utility that creates model classes for you when working with Core Data. I've written about Mogenerator before but what I didn't realize is that I wasn't working with the latest version (the version I was using [...]
by Aral Balkan - Mogenerator latest version, 1.13.1 installer, and build instructions. on 2009-07-13 19:59:09
[...] is a very useful utility that creates model classes for you when working with Core Data. I’ve written about Mogenerator before but what I didn’t realize is that I wasn’t working with the latest version (the version [...]
by Mogenerator latest version, 1.13.1 installer, and build instructions. – 9779th Edition « bölümü fragmanı izle on 2009-07-14 00:13:57
[...] is a very useful utility that creates model classes for you when working with Core Data. I’ve written about Mogenerator before but what I didn’t realize is that I wasn’t working with the latest version (the version [...]
by Mogenerator latest version, 1.13.1 installer, and build instructions. – 9871th Edition « bölümü fragmanı izle on 2009-07-14 08:34:44
[...] is a very useful utility that creates model classes for you when working with Core Data. I’ve written about Mogenerator before but what I didn’t realize is that I wasn’t working with the latest version (the version [...]
by Mogenerator latest version, 1.13.1 installer, and build instructions. – 18378th Edition « bölümü fragmanı izle on 2009-07-14 12:32:38
[...] is a very useful utility that creates model classes for you when working with Core Data. I’ve written about Mogenerator before but what I didn’t realize is that I wasn’t working with the latest version (the version [...]
by Mogenerator latest version, 1.13.1 installer, and build instructions. – 9950th Edition « bölümü fragmanı izle on 2009-07-14 17:05:03
[...] is a great way for automating this process, using mogenerator. The tool can be downloaded as a DMG installer (Aral Balkan’s blog mentions a workaround for older Xcode versions, but for Xcode 3.1.3 it [...]
by nvie.com » Blog Archive » Automatically generate classes for your Core Data data model on 2009-07-30 22:20:41
[...] 1.5 plus trick $ ln -s /Developer/usr/bin/momc [...]
by Der M-Blog - Upgrade to Snow Leopard on 2009-11-29 13:28:53
thank you for point out the real location of momc. it is not updated in Apple's official document.
by mac on 2010-05-04 15:03:02
I've been hunting around for tips and tricks on Core Data, and found this. I've not dug into the specifics of what mogenerator does, but I'm kinda wondering what the point is. You've got the code generation capabilities in Xcode, which allow you to build all of the .h/.m files whenever you make a change to the data model. There's really no need for subclasses, though. I do all of my custom cruft in Categories. This allows me to recreate the entity-based classes whenever I want, without having to worry about overwriting the subclasses, as it appears mogenerator would do everytime you run it. Which is often, given the nature of how data models are built and maintained. Am I missing something? I'm curious, because I think I've found a pretty slick way of doing this kind of work. Do you get extra goodies with mogenerator that make the process easier/more robust? It's a great idea in general, though. And I am definitely interested in getting into the guts of the xcdatamodel, as I would like to be able to generate other data from the model. I went swimming in my model a few days ago, and quickly realized it's a horrifying mess! I'll dig through your site, as you seem to have some interesting insights.
by NukemHill on 2010-10-01 18:42:25