I've got three entities in my application so far: tag, feed and story
A tag has got a to-many relationship to feeds and feeds has got a to-many relationship to story.
I've got an NSArrayController for each entity, one named tags, one named feeds and one named stories.
They all share the same 'managedObjectContext' which they get from the file's owner. the content set of the AC named feeds is bound to 'tags' controler key: selection, key path: feeds
I want the content set of the third array to be bound to all of the stories in all of the feeds in the selected tag: i tried to use the key path: "#unionOfArrays.stories" but couldn't get it to work.
Any idea how i would go about this?
First of all, there's one thing in your question that's inconsistent with getting something working:
They all share the same
'managedObjectContext' which they get
from the file's owner
When I set this up in IB, it just didn't work. You surely mean you bound the managedObjectContext to that of the App Delegate.
Assuming you want to see all the stories in the selected tag, here's a few mistakes you might have made in your setup.
1. Check Inverse Relationships
For all the relationships you mention, you need to set the inverse for each relationship.
For the one to many tags->feeds relationship, you'd have a to many relationship in the tags elements called "feeds", which you've described.
You'd also have a to one relationship in the feeds entity called "tag".
You'd select the inverse relationship as being feeds as shown below:
Single Feed Relationship http://img20.imageshack.us/img20/2557/tagsinglefeedrelationsh.jpg
2. Link Up Stories
You don't mention how you've created any of your Stories. Assuming you're not doing anything in code, I'd have 4 Array Controllers:
Tags
Feeds in Selected Tag
Stories in Selected Feed
All Stories in Selected Tag
If you just have a Stories Array Controller whose Content Set isn't bound to anything, you'll be creating stories effectively in a vacuum - they won't be linked to any feeds or tags, which might be why you're getting these errors.
3. Setup "Stories in Selected Tag" Controller
You need to set the Content Array, not the Content Set.
Bind the Content Array to the "Feeds in Selected Tag" Controller.
Key: arrangedObjects
Key Path: #unionOfArrays.stories
This sends the Key Path stories to every object in the "Feeds in Selected Tag" Controller, thus getting all the Stories in all the Feeds in the selected Tag.
4. Rock and Roll!
We're done. If you're really struggling getting this set up, let me know and I can post the link to the XIB file I've made.
You can try #distinctUnionOfSets.stories. All Core Data 1-n relationships are implemented as sets.
Related
What's the best way to use Core Data if each document on disk corresponds to one Entity instance?
I have a data model file with one entity, and that entity has one attribute of name text and of type Text.
I have a Document.xib that has an NSObjectController that is set to 'Entity' mode and gets the managedObjectContext from the File's Owner. I have an NSTextField that is bound to the Object Controller for the Controller Key 'selection' and the Key Path 'text.' (This is just a test so I can figure out how Core Data works, but my eventual app will also only have one Entity instance per Document)
When I create a new document the textfield says 'No Selection' and is disabled.
I imagine that if I had a Table View or some other kind of way to select from among entity instances the selection would work but I don't nor do I want to. How can I hook up the NSObjectController to only have one Entity instance and to automatically 'select' it?
The intended behaviour is that I type something into the NSTextField, hit Save, close the document, re-open the document and the string in the textfield persists.
This is probably a really basic question but I can't find any tutorials or documents that would address this seemingly simple use case.
Ok, well I haven't figured it all out but my particular issue was being caused by the fact that nothing was being created. I switched out the NSObjectController for an NSArrayController, created an outlet for it in Document.m and added this to windowControllerDidLoadNib:
if (![self.arrayController selectedObjects]) {
[self.arrayController add:#""];
};
Now it seems to just manage the one Entity object.
Core Data model
I have a many-to-many relationship between two of the principal entities; call them Item and Tag. There will be a large number of Documents. Each may have 0 to an arbitrary number of tags.
Each Item entity relevantly has an attribute called name, and a to-many relationship to Tag called tags. Each Tag entity relevantly has an attribute called name, and a to-many relationship to Item called items.
To display them, within the same window, I have: (i) an NSTableView (itemTableView), fed by an NSArrayController (itemArrayController), showing all Items; and (ii) an NSTableView (tagTableView), fed by a different NSArrayController (tagArrayController) showing all Lists.
tagTableView
In the tagTableView, the Table View is bound to tagArrayController, with controllerKey arrangedObjects.
There is only a single table column. The textfield in it is bound to Table Cell View, to model key path objectValue.name. That works so far; it displays all of the lists as expected, and sorts properly when I add a sort descriptor.
Everything has been set up using interface builder in Xcode.
The problem
I have added a checkbox into the tagTableView, in the same table column as the textfield. I am trying to implement two things:
The checkbox should be checked if the user has previously associated the Item with the relevant Tag. If not, the checkbox should be unchecked.
If the user checks an unchecked checkbox, I want to establish a relationship between the two; if the user unchecked a checked checkbox, I want to break that relationship.
The underlying behavior pattern is that the user will not necessarily have control over the tags and may not be able to create them. They are to choose from existing tags, and therefore should be able to see which ones exist, and be able to check/uncheck those that apply.
However, I can't see how to implement this.
Part solutions so far
I can see a possible way to do at least the first task programmatically, roughly along these lines:
Monitor tableViewSelectionDidChange for itemTableView
For a change, update the data source for tagTableView manually, and work out checkbox state by checking them for those Tags which relate to the Item entity that has just been selected, and otherwise unchecking them
However, this looks likely to add complexity, and ideally I would like to do this with bindings if possible.
I have reviewed the Apple Core Data and Bindings references, all the Cocoa books I have, stack overflow and I've also done extensive googling. I have found lots of similar questions (e.g. http://lists.apple.com/archives/cocoa-dev/2011/Mar/msg00164.html) but no answers.
I've also found a way that might work programmatically, but which seems to be like my idea above, at the expense of being able to use bindings (e.g. http://www.raywenderlich.com/14742/core-data-on-ios-5-tutorial-how-to-work-with-relations-and-predicates)
The only relevant question on this site -- Core-Data Check Box Cell with many-to-many data -- is not answered to a level that I can make use of.
It would seem to me that this should be a prime candidate for bindings. I should be able to ask the itemArrayController what Tags (if any) have a relation to its selected item, and then set the checkbox to ticked if it matches the relevant Tag, and unset it if it doesn't. I would expect I should be able to do this within the bindings for the checkbox itself, in interface builder. But I can't work out what model key path or binding to use, or what to set the cocoa bindings for the checkbox to. Am I missing something obvious? Thanks
I have a hasMany relationship between employee-favorites. I can get the store to populate the data structure, but my question is there a way to have the child element (the favorites in this case) be the items for the list item template.
I can use tpl for statement but then all the items are in one list item element. I need one per item element.
There is no out of the box solution for this. The only way to show associations, as you pointed out, is to use a custom tpl which loops through them.
This is because Lists are Store backed components, and stores currently only support 1 type of model.
I have a core data 'ShoppingList' which contains 'Item' objects. I store a display order as an attribute of each item.
I would like to update the display order of all other items in the shopping list whenever an item is deleted. The code to do this is working fine when I use it in my view controller (from where the item is deleted), but since it is really related to the business objects and not the view, it would be better placed in either ShoppingList or Item.
Ideally, I would like it incorporated into the deletion of the item. So far I have tried the following:
1) Customize the standard Core Data generated ShoppingList.RemoveItemsObject (making sure to observe KVO before.after). What's strange about this way is that the item passed is stripped of its relationships to other core data entities before it gets to my code, which I need to process display orders correctly.
2) Customize Item.didTurnIntoFault. Same applies - but even attributes of the item are gone by this stage.
One answer would be to simply define a new method on ShoppingList that does my processing and then calls the original removeItemsObject. But I would prefer to know that whenever an item is removed, from anywhere, this is taken care of. This works nicely when I customize awakeFromInsert, for example - I know that whenever an item is created certain things are setup for me. But I'm surprised there's no equivalent for deletion.
Did you try to implement prepareForDeletion? Sounds like it's exactly what you're looking for.
The doc says:
You can implement this method to perform any operations required before the object is deleted, such as custom propagation before relationships are torn down, or reconfiguration of objects using key-value observing.
I'm using Core Data in my OS X application where I have some TableViews bound to NSArrayControllers. The problem I'm having is when I'm trying to populate a tableview in a sheet using an array controller where I don't want the contents to persist.
Here's how the app hangs together;
Window 1 - Shows a list of users in a table view and allows adding and removing users. Contents persist via Core Data bindings.
Window 2 - Shows a list of groups in a table view. A second table view shows a list of users that belong to the selected group. Contents persist via Core Data bindings. An 'add users' button invokes a sheet for adding users to the group.
Add Users sheet - This sheet shows a table view of users that are not already members of the selected group. Pressing the close button on the sheet adds the selected users to the selected group.
Ok, so the problem I'm having is with the array controller for the Add Users sheet. When I invoke the sheet I iterate through all users and add any to the array controller if they don't already exists in the group. When I close the sheet I try to clear down the array controller using removeObject: but this causes a "can't use this method with a ModelObjectContect."
Why do I need a MOC to remove items from the array controller? It's only for display purposes so I don't need it to persist. If I set the array controllers MOC to that of my app delegate, it physically deletes the users, which I obviously don't want. I just want to remove them from the table view of the sheet.
I thought the answer might be to create another MOC to use as a scratch-pad and not tie it to a persistent store, however this just gave me a different error when using removeObject:, something along the lines of "can't remove objects that exists in another MOC."
Why am I allowed to add object to an array controller but not remove them? In cases where you don't actually want the items physically removed are you supposed to access the the underlying "content", e.g. [arraycontroller content]? I've played with this but get strange display results as it seem to be playing with the array controller's content behind it's back. If I do this, is there a way to tell the array controller "by the way, I've been tinkering with you're content and you may need to get yourself together"?
It looks to me like you shouldn't be using array controllers without Core Data, but there is numerous comments in the documentation that suggests that it works with and without core data.
Yes, you can use an array controller without a Core Data Managed Object Context. But as you're storing NSManagedObject instances inside it, I think it tries to mark them for deletion when you removed them.
If you work with managed objects and don't want the contents of the array controller to be deleted on removal, you have to bind the array controller's content to another object's property with Cocoa Bindings.
But there is a simpler solution. I suggest you to set the managed object context of the array controller to your main MOC and use a predicate to filter its content.
[arrayController setPredicate:[NSPredicate predicateWithFormat:#"NONE groups == %#", group]];
Thus, there is not need to add or remove users from the array controller as all users that are already in the group will be hidden.
You can use them with and without core data, but an array controller either uses core data (entity backed), or it doesn't. I don't think you can use one with managed objects and not have a context.
I'm not clear why you are creating objects instead of just using a fetch request?
You don't say how you are adding the "missing" users but If this is just a basic list, you could consider creating an array of proxy objects (so you aren't touching the MOC) which you can junk when the sheet is done. You could use a non-core data array controller for this, or just (gasp!) not use bindings at all and do it the old fashioned way.
Why not use [arrayController setContent:nil]