Core Data

[carlosefonseca]

Hello,

Is there some way to use JSONModel do create Core Data objects?
The only way I can think is to let JSONModel handle all the JSON work and then copy all the fields to a custom NSManagedObject if the conversion was successful… or is there another way to create the NSManagedObject that I'm not aware of?

Thanks!

[icanzilb]

Hi Carlos, I myself don't have experience with Core Data ... but I'll leave the issue open maybe somebody posts an answer

[carlosefonseca]

I didn't though about that last night but I probably could just make an "NSManagedObjectWithJSONModel" which would be a copy of JSONModel but extending NSManagedObject… that probably works… will check it out when I can…

[jimrutherford]

@carlosefonseca Would be interesting to hear what your solution was to this. I'm about to convert a project that is using JSONModel with an in-memory data model to core data.

[carlosefonseca]

@jimrutherford I haven't played with it again lol :(

[mubeira]

Hi, I know this issue has been already closed for some moths, but I am currently having the same problem Jim is describing on his comment. Has any of you found a proper way of using JSONModel and Core Data?
Any help will be very much appreciated!
Thanx!

[icanzilb]

I use JSONModel and CoreData for few months now. I add a method on each of my JSONModel classes which creates a new CD entity and copies over the fields of the json model to the cd entity class and saves it. I do this once - when the data arrives from the cloud to the app. Then - everything else in the app only uses core data to read data.

[mubeira]

Thank you for your prompt response Marin!
This was my original idea, but a little tedious when you have like me more than 50 entities. I was thinking on a extension to JSONModel. A generic method to make this task by either using a mapping object passed as a parameter or relied on the same approach you used on your library: sharing the same property names on both JSONModel and NSManagedObject to make this transformation.
Many thanks.

[icanzilb]

I was also playing with the same idea, but having a custom method in each model allows me to do special stuff per entity. Like fetch referenced entities from the web which are missing from my local core data.

[mubeira]

Sure, this is why is so powerful, because you can always customize it to cover special cases, but having the generic method shouldn't conflict with this and could be of great use for all those who don't need a different behavior.
By the way, many many thanks for all your work here!

[icanzilb]

I'm planning on a whole different library to provide model storage as a simple alternative to Core Data, that's why I haven't been putting too much effort into cd integration. But unfortunately the next lib is still on the sketching board ... anyways. thanks for the nice words and good luck

[aelam]

JSONModel should make to a tool class with protocol, rather than a root class
like

JSONModelConverter
+ (instancetype)modelFromString:...

JSONModelProcotol
- (NSDictionary *)keywrapper;  

all models need to be convert should implement JSONModelProcotol
then it can be used to NSObject Model and NSManagedObject and others

[pkishino]

Actually I just managed to complete this last night. After first doing the style mentioned above I then finally managed to get the magicalrecord import working. Just need to setup the core model properly with relatedByAttribute and mappedKeyName.
Reading through the wiki entry on this helped. Now all I do is two lines of code, one to create the jsonmodel from json, then create a magicalrecord by importing from the jsonmodel object :)
http://www.cimgf.com/2012/05/29/importing-data-made-easy/

[icanzilb]

@Pziegler oh that sounds cool, can you share some of your code?

[pkishino]

sure:

NSURLSessionDataTask *dataTask = [manager dataTaskWithRequest:request completionHandler:^(NSURLResponse *response, id responseObject, NSError *error) {
        if (error) {
            NSLog(@"Error: %@", error);
            if (completion){
                completion(NO, error,nil);
            }
        } else {
//            NSLog(@"%@ %@", response, responseObject);
            NSArray *items=responseObject[@"posts"];
                [items enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
                    NSError *error=nil;
                    PostModel *model=[[PostModel alloc]initWithDictionary:obj error:&error];
                    Post *post=[model saveToCore];
                    if([post importValuesForKeysWithObject:model])
                            [posts addObject:post];
                }];
                if (completion){
                    completion(YES, nil,[NSArray arrayWithArray:posts]);
                }
        }
    }];
    [dataTask resume];

as you can see I actually DO have a method on the JSONModel called saveToCore as I have a few tricky relationships that I havent quite figures out how to model properly for magicalrecord to import automatically, but I do know that it is possible.
anyways, the main thing is that the CoreData model needs to be mappen something like this:

• NSNumber* oID which is unique,All my JSONModels have one
  My Entity (here Post) has an attribute named oID (Integer_32) and the Entity has a userInfo key: relatedByAttribute : oID
  now I have an author JSONModel object (also with oID) and Author Entity (same userInfo keys as Post).
  The relationship between Post and Author is to-one and inverse to-many. the relationships have each two keys:
  relatedByAttribute : oID AND mappedKeyName : (in the post entity on the author relationship it is : author.oID and inverse post.oID)

thats pretty much it..took me quite a bit of debugging and experimenting before I got it working..the linked blog entry is good..im sure if I had read it more careful first time I would have save a few hours digging but at least I learned a lot more about how magical record works :)
Sorry if my explanation is a bit hard to get, ill post a screenshot: