Sync eases your everyday job of parsing a JSON response and getting it into Core Data. It uses a convention-over-configuration paradigm to facilitate your workflow.
- Handles operations in safe background threads
- Thread-safe saving, we handle retrieving and storing objects in the right threads
- Diffing of changes, updated, inserted and deleted objects (which are automatically purged for you)
- Auto-mapping of relationships (one-to-one, one-to-many and many-to-many)
- Smart-updates, only updates your
NSManagedObjects if the server values are different (useful when usingNSFetchedResultsControllerdelegates) - Uniquing, Core Data does this based on
objectIDs, we use your remote key (such asid) for this
Sync.changes(
changes: [AnyObject],
inEntityNamed: String,
dataStack: DATAStack,
completion: ((NSError?) -> Void)?)+ (void)changes:(NSArray *)changes
inEntityNamed:(NSString *)entityName
dataStack:(DATAStack *)dataStack
completion:(void (^)(NSError *error))completionchanges: JSON responseentityName: Core Data’s Model Entity Name (such as User, Note, Task)dataStack: Your DATAStack
[
{
"id": 6,
"name": "Shawn Merrill",
"email": "shawn@ovium.com",
"created_at": "2014-02-14T04:30:10+00:00",
"updated_at": "2014-02-17T10:01:12+00:00",
"notes": [
{
"id": 0,
"text": "Shawn Merril's diary, episode 1",
"created_at": "2014-03-11T19:11:00+00:00",
"updated_at": "2014-04-18T22:01:00+00:00"
}
]
}
][Sync changes:JSON
inEntityNamed:@"User"
dataStack:dataStack
completion:^(NSError *error) {
// New objects have been inserted
// Existing objects have been updated
// And not found objects have been deleted
}];Alternatively, if you only want to sync users that have been created in the last 24 hours, you could do this by using a NSPredicate.
NSDate *now = [NSDate date];
NSDate *yesterday = [now dateByAddingTimeInterval:-24*60*60];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"createdAt > %@", yesterday];
[Sync changes:JSON
inEntityNamed:@"User"
predicate:predicate
dataStack:dataStack
completion:^{
//...
}];
Sync is available through CocoaPods. To install it, simply add the following line to your Podfile:
use_frameworks!
pod 'Sync'Replace your Core Data stack with an instance of DATAStack.
self.dataStack = [[DATAStack alloc] initWithModelName:@"Demo"];Then add this to your App Delegate so everything gets persisted when you quit the app.
- (void)applicationWillTerminate:(UIApplication *)application {
[self.dataStack persistWithCompletion:nil];
}Sync requires your entities to have a primary key, this is important for diffing, otherwise Sync doesn’t know how to differentiate between entries.
By default Sync uses id from the JSON and remoteID from Core Data as the primary key. You can mark any attribute as primary key by adding hyper.isPrimaryKey and the value YES.
For example, in our Designer News project we have a Comment entity that uses body as the primary key.
Your attributes should match their JSON counterparts in camelCase notation instead of snake_case. For example first_name in the JSON maps to firstName in Core Data and address in the JSON maps to address in Core Data.
There are two exceptions to this rule:
ids should matchremoteID- Reserved attributes should be prefixed with the
entityName(typebecomesuserType,descriptionbecomesuserDescriptionand so on). In the JSON they don't need to change, you can keeptypeanddescriptionfor example. A full list of reserved attributes can be found here
If you want to map your Core Data attribute with a JSON attribute that has different naming, you can do by adding hyper.remoteKey in the user info box with the value you want to map.
To map arrays or dictionaries just set attributes as Binary Data on the Core Data modeler.
{
"hobbies": [
"football",
"soccer",
"code"
]
}NSArray *hobbies = [NSKeyedUnarchiver unarchiveObjectWithData:managedObject.hobbies];
// ==> "football", "soccer", "code"{
"expenses" : {
"cake" : 12.50,
"juice" : 0.50
}
}NSDictionary *expenses = [NSKeyedUnarchiver unarchiveObjectWithData:managedObject.expenses];
// ==> "cake" : 12.50, "juice" : 0.50We went for supporting ISO8601 and unix timestamp out of the box because those are the most common formats when parsing dates, also we have a quite performant way to parse this strings which overcomes the performance issues of using NSDateFormatter.
NSDictionary *values = @{@"created_at" : @"2014-01-01T00:00:00+00:00",
@"updated_at" : @"2014-01-02",
@"published_at": @"1441843200"
@"number_of_attendes": @20};
[managedObject hyp_fillWithDictionary:values];
NSDate *createdAt = [managedObject valueForKey:@"createdAt"];
// ==> "2014-01-01 00:00:00 +00:00"
NSDate *updatedAt = [managedObject valueForKey:@"updatedAt"];
// ==> "2014-01-02 00:00:00 +00:00"
NSDate *publishedAt = [managedObject valueForKey:@"publishedAt"];
// ==> "2015-09-10 00:00:00 +00:00"Sync's dependency NSManagedObject-HYPPropertyMapper provides a method to generate a JSON object from any NSManagedObject instance. More information here.
Sync will map your relationships to their JSON counterparts. In the Example presented at the beginning of this document you can see a very basic example of relationship mapping.
Lets consider the following Core Data model.
This model has a one-to-many relationship between User and Note, so in other words a user has many notes. Here can also find an inverse relationship to user on the Note model. This is required for Sync to have more context on how your models are presented. Finally, in the Core Data model there is a cascade relationship between user and note, so when a user is deleted all the notes linked to that user are also removed (you can specify any delete rule).
So when Sync, looks into the following JSON, it will sync all the notes for that specific user, doing the necessary inverse relationship dance.
[
{
"id": 6,
"name": "Shawn Merrill",
"notes": [
{
"id": 0,
"text": "Shawn Merril's diary, episode 1",
}
]
}
]A similar procedure is applied to one-to-one relationships. For example lets say you have the following model:
This model is simple, a user as a company. A compatible JSON would look like this:
[
{
"id": 6,
"name": "Shawn Merrill",
"company": {
"id": 0,
"text": "Facebook",
}
}
]As you can see this procedures require the full JSON object to be included, but when working with APIs, sometimes you already have synced all the required items. Sync supports this too.
For example, in the one-to-one example, you have a user, that has one company. If you already have synced all the companies then your JSON would only need the company_id. As a sidenote only do this if you are 100% sure that all the required items (companies) have been synced.
[
{
"id": 6,
"name": "Shawn Merrill",
"company_id": 0
}
]You are free to use any networking library.
- iOS 8 or above
- OS X 10.9 or above
- watchOS 2.0 or above
- tvOS 9.0 or above
Sync wouldn’t be possible without the help of this fully tested components:
-
DATAStack: Core Data stack and thread safe saving
-
DATAFilter: Helps you purge deleted objects. Internally we use it to diff inserts, updates and deletes. Also it’s used for uniquing Core Data does this based on objectIDs, DATAFilter uses your remote keys (such as id) for this
-
NSManagedObject-HYPPropertyMapper: Maps JSON fields with their Core Data counterparts, it does most of it’s job using the paradigm “convention over configuration”
Well, the thing is that if you add hyper.isPrimaryKey it would use the normal attribute for the local primary key, but the remote primary key is the snake_case representation of it. Some people might expect that the local keeps been the same (remoteID), or that the remote keeps been the same (id).
For example if you add the flag hyper.isPrimaryKey to the attribute article_body then:
- Remote primary key:
article_body - Local primary key:
articleBody
If you want to use id for the remote primary key you also have to add the flag hyper.remoteKey and write id as the value.
In a one-to-many relationship IDs are unique for a parent, but not between parents. For example in this example we have a list of posts where each post has many comments. When syncing posts 2 comment entries will be created:
[
{
"id": 0,
"title": "Story title 0",
"comments": [
{
"id":0,
"body":"Comment body"
}
]
},
{
"id": 1,
"title": "Story title 1",
"comments": [
{
"id":0,
"body":"Comment body"
}
]
}
]
```
Meanwhile in a `many-to-many` relationship childs are unique across parents.
For example a author can have many documents and a document can have many authors. Here only one author will be created.
```json
[
{
"id": 0,
"title": "Document name 0",
"authors": [
{
"id":0,
"name":"Michael Jackson"
}
]
},
{
"id": 1,
"title": "Document name 1",
"authors": [
{
"id":0,
"body":"Michael Jackson"
}
]
}
]
```
#### Logging changes:
Logging changes to Core Data is quite simple, just subscribe to changes like this and print the needed elements:
```objc
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(changeNotification:)
name:NSManagedObjectContextObjectsDidChangeNotification
object:self.dataStack.mainContext];
- (void)changeNotification:(NSNotification *)notification {
NSSet *deletedObjects = [[notification userInfo] objectForKey:NSDeletedObjectsKey];
NSSet *insertedObjects = [[notification userInfo] objectForKey:NSInsertedObjectsKey];
}
```
Logging updates is a bit more complicated since this changes don't get propagated to the main context. But if you want an example on how to do this, you can check the AppNet example, [the change notifications demo is in the Networking file](https://github.com/hyperoslo/Sync/blob/master/AppNet/Networking.swift#L27-L57).
If you're using Swift to be able to use `NSNotificationCenter` your class should be a subclass of `NSObject` or similar.
#### Crash on NSParameterAssert
This means that the local primary key was not found, Sync uses `remoteID` by default, but if you have another local primary key make sure to mark it with `"hyper.isPrimaryKey" : "YES"` in your attribute's user info. For more information check the [Primary Key](https://github.com/hyperoslo/Sync#primary-key) section.
```objc
NSString *localKey = [entity sync_localKey];
NSParameterAssert(localKey);
NSString *remoteKey = [entity sync_remoteKey];
NSParameterAssert(remoteKey);
```
## Credits
[Hyper](http://hyper.no) made this. We’re a digital communications agency with a passion for good code and delightful user experiences. If you’re using this library we probably want to [hire you](https://github.com/hyperoslo/iOS-playbook/blob/master/HYPER_RECIPES.md) (we consider remote employees too, the only requirement is that you’re awesome).
## License
**Sync** is available under the MIT license. See the [LICENSE](https://github.com/hyperoslo/Sync/blob/master/LICENSE.md) file for more info.