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Note: these techniques depend on deprecated technologies. Use at your own risk. - Mike Schrag
A CocoaEOApplication (formally, in WO 5.2, Cocoa Enterprise Objects Application, but here simply CEO) is a set of objects which allow you to use the Enterprise Objects Framework (EOF) inside Cocoa. Even though the technology is not yet supported by Apple, it had been around since NeXT was independent.
In its previous versions, CEO uses Objectve-C as its primary language (which is now the primary language of Cocoa), but since WO 5.0 the main language to use EOF is Java. In order to use EOF within Cocoa (in particular, in order to use EOModeler in OSX), Apple developed the so-called Java-Bridge (see e.g., http://cocoadevcentral.com/articles/000024.php ---there was a document entitled "Using the Java Bridge", but at the time I am writing this (Jul 24 2003), it was not available any more in developer.apple.com; however you may find a copy in your hard disk under /Developer/Documentation/JavaBridge/JavaBridge.pdf). In order to develope a CEO, you will have to get used to its mechanisms.
Update (Jun 3, 2005): the JavaBridge.pdf is now in http://developer.apple.com/documentation/Cocoa/Conceptual/Legacy/JavaBridge/JavaBridge.pdf_
There are some things you have to be aware when creating a CEO project (this note is for WO 5.2 and has been revisted for 5.2.2 ---and now for WO 5.2.4):
When you launch the Project Builder's wizard and ask for a Cocoa/EO application, it will create an unusable MainMenu.nib file. To solve the problem: close your project; delete the "corrupted" file MainMenu.nib (it is inside the English.lproj folder of your project); launch Interface Builder and create an Empty interface; save it as MainMenu.nib (better with the extension) in the same place where the "corrupted" file was; re-launch Project Builder; Done.
The first time you drag an entity from EOModeler into Interface Builder, an EOEditingContext will be created for you (if you drag the entity onto a window, an NSTableView and an EODisplayGroup will also be created; if you do onto the class-viewer, only the EODisplayGroup will be created). The default (not always desirable) is to "fetch on load" all the objects in the entity; if you do not want this, go to the inspector (with the EODisplayGroup selected) and uncheck the corresponding button.
Basically, you are there. You can use all actions of your display groups and your editing context to see and manipulate your database, without writing a single line of code ---in fact, you do not have neither to compile your project; simply connect your buttons and run the "Test Interface" command from the file menu (or cmd+r from the keyboard) and you will see your database showing up.
Of course, if you are an experienced programmer and want to add some "logic" to your app, you can do it. The first thing you have to do, is to choose a language; I prefer Obj-C, but also Java can be used... in fact it will be used even if you decide not to. The EOF had been written in pure Java so, even if you do not write a single line of code in Java (which some times seems unavoidable), you will be using it via the Java Bridge. I'll be back on this later...
Following the recomendation of a virtual-friend (Arturo Perez), I decided to add a simple guide to build up a CEO.
It is really simple... almost as simple as D2W, but more beauty.
Have a model? if so, you can manipulate your db with out writing a single line of code.
Try the following:
Your table will show up!!
If you are familiar with IB, the reset is history, but in case you are not, you can try:
You will see a new row in your table!!
Do you want to add some custom logic?
You will compile and run your new app. After the table shows up, push the (second) button.
That's it!! You are now ready to develope the best apps in the market ;^()
If you know you are going to require tones of memory, or you get the "java.lang.outOfMemoryError"; message in your console, or your app is simply not doing what it is supposed to, you may need to read this section... otherwise, simply jump it.
Are you still here? well, your problem may be that the VJM did not allocate enough memory for you.
In Project Builder, under targets and with the main target selected, go to Info.plist Entries > Pure-Java Specific (in Xcode, you have to click the little triangle of the targets group, double-click the main target). Add in the "Additional VM Options" text field something like
(This will give to your JVM 256Mb of memory instead of 64Mb, the default.)
Also, it is convenient that you get used to use NSAutoreleasePool properly (see its documentation and related topics; in particular, read Chapter 4 of the book "The Objective-C Programming Language" http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC). The Java Bridge does a good work using "garbage Collection" in the Java side, and "reference count" in the Obj-C side; just do not worry about that.
For those objects comming from com.apple.cocoa.foundation.* you really does not have to take care (with the remarkable exception of NSEnumerator); they go forth and back nicely. Even do some simple objects like String (which maps to NSString), Number (which maps to NSNumber) and some basic types like int, char, boolean and so.
So far, so good. However, be carefull when you want to enumarate an array. In the one hand, if the array was created in the Obj-C side and you ask for an objectEnumerator, you will recive an NSEnumerator. This object implements the method nextObject to traverse the elements of the array. On the other hand, if the array was created in the Java side (e.g., as a result of an allObjects() call) and you ask for an objectEnumerator, you will recive an Enumerator object which implements the nextElement() method instead.
Some examples of the two scenarios are the following.
An Obj-C array:
A Java array:
These simple examples show some things to have in mind when developping a CEO:
Therefore, you most create FIRST the array and, once allocated, use it as argument. An important example is the class method qualifierWithQualifierFromat(String format, NSArray arguments) implemented by com.webobjects.eocontrol.EOQualifier. I'll be back with this isue later...
Maybe the worst part of the CEO integration is the managment of arrays; there are 5 types of array you most be aware:
A C array of objects (like id array).
A Java array of objects (like Object).
This is too much!!!! But life is life, and beter get used to them...
Usually, when you are not intended to use EOF inside Cocoa, you can forget about the array in com.webobjects.foundation; the bridge translates, by default, that of Foundation.h to com.apple.cocoa.foundation, back and forth, with no problem... well, almost: from Java to Obj-C each array go as an NSCFArray which is documented NOWARE, but it works as an NSArray. On the other side, from Obj-C to Java, they go as com.apple.cocoa.NSMutableArray which inherits from the usual NSArray ---try to print their classes description in both sides after they had traveled the bridge with the following code:
This is not as bad as it may seems. In practice, you do not have to be aware of this.
The real problem start when you want to use EOF. Most of the Enterprise Objects (defined somewhere in com.webobjects.*), when use an array, they are waiting for a com.webobjects.foundation.NSArray and non of the above.
There are many solutions to this problem. The first one (for those who knows Java and Obj-C) is to have a bridgeTool.java object in charge of allocating those arrays as neaded:
And call this method from your Obj-C object with something like
Once you have your woArray, you can use it as an argument in Enterprise Objects' calls.
I had not foud the way to call a Java method which has an Object array as argument. If someone reading this finds out, please let us know...
When working with EOF, there are several points when you will want to build a qualifier to perform a fetch. A qualifier is an instance of com.webobjects.eocontrol.EOQualifier. If your qualifier does not include any date, then it is as easy as
and then use it in a fetch specification with
On the other hand, if you want to use a date in your qualifier, since NSCalendarDate is not properly translated to NSTimestamp, you have to use again the bridgeTool.java trick:
and call this from Obj-C by
(just be consistent with your formats).
It is also possible (at least in WO 5.2.4 running on Tiger) to use
com.webobjects.eointerface.cocoa.EOCocoaUtilities as follows:
From here, you can use the nsTimestamp as argument in those classes defined in com.webobjects.* (e.g., in your qualifiers).
Let us start this section describing how to put together two of the most powerful frameworks of OS X; namely, EOF and the NSDocument framework (this section was written, in July 2005, while working in WO 5.2.4 running on Tiger) ---later on, we will integrate these with Core Data which I think that, jointly with Bindings, will substitute EOF in the near future.
Let us do it as a "tutorial":
Basically you are done. However, if you --like me-- prefer to work in Objective-C, then do the following:
Compile and run (cmd+r).
Finally, if you will, you can get rid of the warnings about deprecated methods in the .java file created by the wizard:
Compile and run (cmd+r).
By this moment, you had created a multi-document CEO...