I have an entity named Geometry which is related to a Plot entity. In our piece of code, given the Plot and some downloaded data stored in a NSDictionary, we must get the Geometry and set some NSString properties but, after doing that, I find that the relationship between entities is lost.
NSError * saveError = nil;
NSFetchRequest * request = [[NSFetchRequest alloc] initWithEntityName:[Geometry entityName]];
request.predicate = [NSPredicate predicateWithFormat:#"plot == %#", plot];
NSError * error = nil;
NSArray * results = [context executeFetchRequest:request error:&error];
Geometry * __block geometry = nil;
if ([results count] > 0) {
[results enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL * stop) {
Geometry * geometryObject = obj;
if ([geometryObject.gid isEqualToString:[NSString stringWithFormat:#"%#", [data valueForKey:#"gid"]]]) {
geometry = geometryObject;
stop = YES;
}
}];
}
if (geometry != nil) {
[geometry setPolygon:[NSString stringWithFormat:#"%#", [data valueForKey:#"polygon"]]];
}
if (![context save:&saveError]) {
NSLog(#"%#", saveError);
}
The first time I run this code results have one object, but the next time I run this there is no results.
Assume everything outside the scope of this piece of code is working right. Any hint or clue about why this happen? How can I solve this?
EDIT: The problem has been solved outside the scope of the code posted and outside the scope of this question. I should have properly reviewed the code further.
There is nothing in your code that breaks the relationship. The error must be elsewhere.
You have a Plot object, so you can get the geometries with plot.geometries without a fetch request, and filter them without a loop:
Geometry *geometry = [plot.geometries
filteredArrayUsingPredicate: [NSPredicate predicateWithFormat:#"gid = %#", gidString]]
.firstObject
where geometries is the name of the inverse relationship for plot.
You can now set the polygon property and save. Check your setPolygon method if you are not removing the relationship.
Related
After I updated the Core data with the right value, i would like to add these value to the map view.
This the code that a I'd wrote for doing this it's this:
-(void)updateMapWithPredicate:(NSPredicate *)predicate
{
int numberOfElementiOnMap = 0;
dispatch_async(dispatch_get_main_queue(), ^{
[self.ActiviIndicator startAnimating];
[self.mapView removeAnnotations:self.mapView.annotations];
});
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:#"Photo"];
if (predicate) {
request.predicate = [NSCompoundPredicate andPredicateWithSubpredicates:#[[NSPredicate predicateWithFormat:#"(latitude != nil) AND (longitude != nil)"]
,predicate]];
} else {
request.predicate = [NSPredicate predicateWithFormat:#"(latitude != nil) AND (longitude != nil)"];
}
//Get all different coordinate from core data.
[request setPropertiesToFetch:#[#"latitude", #"longitude"]];
[request setReturnsDistinctResults:YES];
[request setResultType:NSDictionaryResultType];
// Execute the fetch
NSError *error = nil;
NSArray *photos = [self.context executeFetchRequest:request error:&error];
for (NSDictionary *coordinateDic in photos) {
NSPredicate *predicateToSend;
if (predicate) {
/* Get all pictures that corresponding to the coordinate inside the coordinateDic
*/
predicateToSend = [NSCompoundPredicate andPredicateWithSubpredicates:#[[NSPredicate predicateWithFormat:#"(latitude == %#) AND (longitude == %#)",
[coordinateDic valueForKey:#"latitude"], [coordinateDic valueForKey:#"longitude"]],predicate]];
} else {
predicateToSend = [NSPredicate predicateWithFormat:#"(latitude == %#) AND (longitude == %#)",[coordinateDic valueForKey:#"latitude"], [coordinateDic valueForKey:#"longitude"]];
}
dispatch_async(dispatch_get_main_queue(), ^{
//get all picture with the same lautide and longitude that are specified on predicate
NSArray *photos2 = [Photo pictureFromContext:self.context withPredicate:predicateToSend];
//if the pictures are more then one, we add only one picture, and we write the number of pictures as a subtitle of the mkannotationview
if ([photos2 count] > 1) {
Photo *photo = [photos2 lastObject];
photo.photoDescription = [NSString stringWithFormat:#"album with %lu picures",(unsigned long)[photos2 count]];
if (photo) {
// [self.mapView addAnnotation:photo];
}
} else { //add the only pictures
if ([photos2 firstObject]) {
[self.mapView addAnnotation:[photos2 firstObject]];
}
}
});
}
}
On this code i basically retrieve the value that in need from core date, and then add it to the map.
The objects that I'm adding to the map are obviously conform to the <MKAnnotation> protocol. I got the error on the [self.mapView addAnnotation:[photos2 firstObject]];line. The strange fact is that some object that i get from core date are correctly added to the map. I tried to debug the code by enabling the NSZombie but i got the same error. I also check the coordinate and everything it's all right. The only difference that i found while I'm debugging the code it's this:
The object that are added correctly to the maps looks like this in the debugger:
Instead when i get the error, the object that I'm adding to the map looks like this on the simulator:
and when i print the content of: 0 i get this:
Printing description of *([0]->[0]):
(Photo_Photo_) [0] = {}
which it's look like a pointer to an empty entity.
do you have any idea of how can i solve this?
Thanks
After submitting the bug report Apple told me the solution for my problem. The problem was that i was updating the coordinate in a non KVO compliant way. I store the properties like you, with latitude and longitude. Try adding this on your Photo class.
- (void)willChangeValueForKey:(NSString *)key
{
if ([key isEqualToString:#"latitude"] || [key isEqualToString:#"longitude"]) { [self willChangeValueForKey:#"coordinate"]; }
[super willChangeValueForKey:key];
}
- (void)didChangeValueForKey:(NSString *)key
{
if ([key isEqualToString:#"latitude"] || [key isEqualToString:#"longitude"]) { [self didChangeValueForKey:#"coordinate"]; }
[super didChangeValueForKey:key];
}
Hope this helps.
I have a problem checking whether a particular attribute of an Entity exists in the Core Data Database (through predicates) before creating a new object; if the object exists, I'd rather return it than create a new object.
I have a simple App which has a table view with a plus button in the Navigation Bar; the user clicks that and is presented with a View Controller with 4 text fields. They fill in that information, press save and it gets saved to Core Data and displayed in the TableView (through the use of NSFetchedResultsControllers).
The data model is as follows:
Transaction Entity with isReceived BOOL attribute
Person Entity with name string attribute
Occasion Entity with title string attribute
Item Entity with amount string attribute
The transaction has a relationship to the Person (whoBy), Occasion (Occasion) and Item entities.
In the view controller with the save method, I have the code below which will insert new objects into the Transaction, Person, Occasion Entities, etc. Each Transaction is of course unique, but with each transaction, the user can select an existing PERSON and/or Occasion and if that person then does not exist, it will be created (likewise with the occasion).
I'm slightly confused as to the format of the code here.
EDIT: I have tried a combination of code and can just not get this working. In the code below, I'm referencing person.name in the predicate, but I also tried creation a local NSString variable to hold the self.nameTextField.text code but that did nothing. I tried creating a NSString property to reference it that way and that not work. I tried using the words MATCHES, LIKE, CONTAINS, == and every combination in-between.
- (IBAction)save:(id)sender
{
NSManagedObjectContext *context = [self managedObjectContext];
Transaction *transaction= [NSEntityDescription insertNewObjectForEntityForName:#"Transaction" inManagedObjectContext:context];
Person *person = [NSEntityDescription insertNewObjectForEntityForName:#"Person" inManagedObjectContext:context];
Occasion *occasion = [NSEntityDescription insertNewObjectForEntityForName:#"Occasion" inManagedObjectContext:context];
Item *amount = [NSEntityDescription insertNewObjectForEntityForName:#"item" inManagedObjectContext:context];
NSFetchRequest *personFind = [NSFetchRequest fetchRequestWithEntityName:#"Person"];
personFind.predicate = [NSPredicate predicateWithFormat:#"name == %#", person.name];
// I have tried every combination of the predicate like MATCHES, LIKE.
// I created a local NSString variable and an NSString property
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:#"name" ascending:YES];
personFind.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];
NSError *error = nil;
NSArray *matches = [context executeFetchRequest:personFind error:&error];
if (!matches || ([matches count] > 1))
{
// Handle Error
}
else if ([matches count] == 0)
{
person.name = self.nameTextField.text;
transaction.whoBy = person;
occasion.title = self.occasionTextField.text;
transaction.occasion = occasion;
}
else
{
person = [matches lastObject];
transaction.whoBy = person;
occasion.title = self.occasionTextField.text
transaction.occasion = occasion;
}
if (![context save:&error])
{
NSLog(#"Can't save! %# %#", error, [error localizedDescription]);
}
[self dismissViewControllerAnimated:YES completion:nil];
}
Logically, what I want to achieve is:
When the user is adding a Transaction, check if it's for a new person or an existing one — if it's an existing one, choose it from a list of Persons (and when the user selects a person, get its NSManagedObjectID). If it's a new one, create it on the spot.
The same for the Occasion.
Set all the other fields of the Transaction object (amount, etc.).
My question is:
What predicate do I use to get this working?
When I put a break point in this method, a NEW NAME (one that doesn't exist before) correctly calls the else if ([matches count] == 0) method and if I create an entry with an existing name, it calls the
else
{
person = [matches lastObject];
transaction.whoBy = person;
occasion.title = self.occasionTextField.text
transaction.occasion = occasion;
}
Even with the this statement, it is still creating a new person object for the same name.
I will correctly implement the occasion after getting the person working, but I'm just lost on how to get this working.
Any help would be massively appreciated!
"Is this correct?":
No. You are creating a new Person and Occasion objects whether you are using an existing person/occasion or not.
First check for existence and only if the object not already exist, insert a new one.
Alternatively, if the person/occasion exist, delete the inserted object.
"How do I retrieve the managedObjectID for person/event?":
Person* person = /*Get an existing person object*/
NSManagedObjectID* personId = person.objectID /*This is the person object ID, will work for any NSManagedObject subclass*/
To find a person that start with a string str use this predicate in a fetch request:
/*UNTESTED*/
[NSPredicate predicateWithFormat:#"(name BEGINSWITH[cd] %#)", str];
Edit:
To be more precise, you practice find or create using something like this:
(this is very limited, and only good for a single object performance-wise)
(NOT TESTED)
- (NSManagedObject*) findOrCreateObjectByValue:(id)value
propertyName:(NSString*)propertyName
entityName:(NSString*)entityName
additionalInfo:(NSDictionary*)additionalInfo
context:(NSManagedObjectContext*)context
error:(NSError* __autoreleasing*)error
{
NSManagedObject* res = nil;
NSFetchRequest* r = [NSFetchRequest fetchRequestWithEntityName:entityName];
[r setPredicate:[NSPredicate predicateWithFormat:#"%K == %#",propertyName,value]];
NSArray* matched = [context executeFetchRequest:r
error:error];
if (matched) {
if ([matched count] < 2) {
res = [matched lastObject];
if (!res) { //No existing objects found, create one
res = [NSEntityDescription insertNewObjectForEntityForName:entityName
inManagedObjectContext:context];
[res setValue:value
forKey:propertyName];
[res setValuesForKeysWithDictionary:additionalInfo];
}
} else {
if (error) {
*error = [NSError errorWithDomain:#"some_domain"
code:9999
userInfo:#{#"description" : #"duplicates found"}];
}
}
}
return res;
}
So now, your save: method should look something like:
(I assume here that the person name and occasion title are held by a UITextField on the view controller [txtPersonName and txtOccasionTitle respectively] )
- (void) save:(id)sender
{
//create a clean context so that changes could be discarded automatically on failure
NSManagedObjectContext* context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
[context setParentContext:[self managedObjectContext]];
//A Transaction is always created in save event, so add it to the context
Transaction* transaction = [NSEntityDescription insertNewObjectForEntityForName:#"Transaction" inManagedObjectContext:context];
__block NSError* error = nil;
Person* p = (Person*)[self findOrCreateObjectByValue:self.txtPersonName.text
propertyName:#"name"
entityName:#"Person"
additionalInfo:nil
context:context
error:&error];
if (!p) {
NSLog(#"Error: %#, person name: %#",error,self.txtPersonName.text);
return;
}
Occasion* o = (Occasion*)[self findOrCreateObjectByValue:self.txtOccasionTitle.text
propertyName:#"title"
entityName:#"Occasion"
additionalInfo:nil
context:context
error:&error];
if (!o) {
NSLog(#"Error: %#, occasion title: %#",error,self.txtOccasionTitle.text);
return;
}
transaction.whoBy = p;
transaction.occasion = o;
//Not sure what you are using this property for
transaction.item = [NSEntityDescription insertNewObjectForEntityForName:#"Item"
inManagedObjectContext:context];
NSManagedObjectContext* ctx = context;
if ([context obtainPermanentIDsForObjects:[context.insertedObjects allObjects]
error:&error])
{
//save your changes to the store
__block BOOL saveSuccess = YES;
while (ctx && saveSuccess) {
[ctx performBlockAndWait:^{
saveSuccess = [ctx save:&error];
}];
ctx = [ctx parentContext];
}
if (!saveSuccess) {
NSLog(#"Could not save transaction, error: %#",error);
}
} else {
NSLog(#"Could not obtain IDs for inserted objects, error: %#",error);
}
//Do what you have to do next
}
This is just for making things a bit clearer on what you should do to avoid duplications, and reuse existing objects.
I have two entities, one called InProject that has several attributes and one relationship. the relationship is with another entity called Ins.
I am editing one of the Ins that is related to InProject. I used InProject attribute ID which then returns a NSDictionary value that has several key-values one of which is for an array of Ins. I then find the Ins I need to edit in a for loop I edit them, but then I become unstuck because I am not sure how to save the contect of InProject with the *updated Ins
I need to figure out how to save InProject after I have overwritten the Ins attributes I need to update.
This is what my code looks like after battling this problem:
- (void)editSelectedins:(NSString *)projIDString UpdatedNSD:(NSMutableDictionary *)updatedNSD DPC:(int)dpc{
// get context
NSManagedObjectContext *context = [self managedObjectContext];
if (context == nil) {
NSLog(#"Nil");
}
else {
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"InsProject" inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSError *error;
NSMutableArray *InsProjectDictionaryArray = [[NSMutableArray alloc] init];
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
for (InsProject *insProj in fetchedObjects) {
NSMutableDictionary *tempInsProjectDictionaryArray = [[ NSMutableDictionary alloc] init];
[tempInsProjectDictionaryArray setObject:insProj.companyName forKey:#"CompanyName"];
[tempInsProjectDictionaryArray setObject:insProj.projNo forKey:#"ProjNo"];
[tempInsProjectDictionaryArray setObject:insProj.desc forKey:#"Desc"];
[tempInsProjectDictionaryArray setObject:insProj.guid forKey:#"GUID"];
[tempInsProjectDictionaryArray setObject:insProj.projID forKey:#"ProjID"];
[tempInsProjectDictionaryArray setObject:insProj.ins forKey:#"ins"];
[InsProjectDictionaryArray addObject:tempInsProjectDictionaryArray];
}
// now that you have the InsProjects, choose the one you are curently working on in insView using the projectID
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"ProjID==%#",projIDString];
[fetchRequest setPredicate:predicate];
// new array with one value that was created using the NSPredicate ProjID
NSArray *tempInsProjectArray = [InsProjectDictionaryArray filteredArrayUsingPredicate:predicate];
// get ins array out of the NSDictionary to edit
NSSet *inssForInsProject = tempInsProjectArray[0][#"ins"];
NSMutableArray *tempAllinss = [[NSMutableArray alloc] init]; // this will contain everything, that means all repeated values are included
for (Items* currItem in [inssForInsProject allObjects]) {
NSArray *keys = [[[currItem entity] attributesByName] allKeys];
NSDictionary *dict = [currItem dictionaryWithValuesForKeys:keys];
[tempAllinss addObject:dict];
}
NSArray *myArray = [tempAllinss copy];
// get the correct items from myArray anything whos dpc matches the dpc parameter of this method
NSMutableArray *editedinsArray = [[NSMutableArray alloc] init];
for (int i = 0; i < [myArray count]; i++) {
NSMutableDictionary *tempinssDictionary = [myArray objectAtIndex:i];
// if you get a match put it into the new editedinsArray to be edited
if ([[tempinssDictionary objectForKey:#"dpc"] integerValue] == dpc) {
[editedinsArray addObject:tempinssDictionary];
}
}
// by now you should have three things
// 1, access to your ins coredata object //this s wrong I actually have access to insProject
// 2, the values you need to be edited saved into a NSArray (editedinsArray, which will be used to check against and keep old values correct)
// 3, UpdatedNSD which will be used to update any values that need to be updated.
// go through your values and update the ins object
int i = 0;
for (ins *temp in editedinsArray) {
NSDictionary *currentEditedins = [editedinsArray objectAtIndex:i];
i++;
// these values should stay the same so use currentEditedins which contains old vals
NSString *stringToNumberDpc = [currentEditedins valueForKey:#"dpc"];
int tempDpcNum = [stringToNumberDpc integerValue];
NSNumber *dpcNumber = [NSNumber numberWithInt:tempDpcNum];
temp.dpc = dpcNumber;
NSString *totDQtyString = [currentEditedins valueForKey:#"totDQty"];
if ((NSNull *)totDQtyString == [NSNull null]) {
temp.totDQty = #"";
} else {
temp.totDQty = totDQtyString;
}
NSString *totShipString = [currentEditedins valueForKey:#"totShip"];
if ((NSNull *)totShipString == [NSNull null]) {
temp.totShip = #"";
} else {
temp.totShip = totShipString;
}
// values to be updated so use updatedNSD wthich was passed in as method param with the new vals
temp.newInsComp = [updatedNSD valueForKey:#"newInsComp"];
temp.newDryComp = [updatedNSD valueForKey:#"newDryComp"];
temp.updatedRow = [updatedNSD valueForKey:#"updatedRow"];
}
#warning --- I have no idea what to do here... i.e. how do I update the tempInsProjectArray.ins values I have just updated in the above for loop then save context which I hope would update insProj and the ins entities involved.
//save
[context save:&error];
}
}
As you can see at the bottom of the code with #warning I explain where I am having the issue. if I log temp inside the for loop I see the updated values perfectly the issue I am having is how do I then update the current tempInsProjectArray.ins values that I have just edited? then save them of course.
Your code is in great need of simplification. Some ground rules:
Use names with smallInitial and camelCase for variables. So not InsProjectDictionaryArray but insProjectDictionaryArray.
The same applies to dictionary keys indicating attribute names of managed objects. So projNo, not ProjNo.
Avoid cryptic abbreviations. Use plain and readable English Not projNo but projectNumber. What is an Ins? What is "dcp"?
Don't use the plural form for entity names. An suitable name for an item is Item, not Items
Don't use the mutable versions of dictionary and array when immutable ones would do.
Avoid duplicating your data, such as in [array copy].
Avoid dictionaries when you have an object graph. The object graph is what core data creates. It renders dictionaries with values and keys unnecessary.
Don't use IDs. The object graph renders those unnecessary as well in most cases. If you use IDs, do not use strings but numbers, such as long ints, or the object version NSNumber.
When fetching data from the Core Data persistent store, don't fetch all the data and the filter the result. Fetch only the data you need.
What you want to accomplish can surely be done in a few lines of code. I will try to summarize what you want to do as far as I understand it.
Your data model looks something like this:
Project <----->> Item
Where the items are in a to-many relationship called ins. I will rename this items. I will also assume that you will refactor your IDs to be of type NSNumber.
All the code up to myArray could be substituted with this:
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:"Project"];
request.predicate = [NSPredicate predicateWithFormat:#"projectID = %#", projectID];
request.fetchLimit = 1;
NSArray *fetchedObjects = [self.managedObjectContext
executeFetchRequest:request error:nil];
Project *project = fetchedObjects[0];
You now have all items available simply with project.items. I understand that there could be more than one item with a mysterious attribute dcp of type int (i.e. NSNumber for managed objects), that is equal to the dcp parameter passed.
NSSet *matchingItems = [project.items filteredSetUsingPredicate:
[NSPredicate predicateWithFormat:#"dcp = %#", #(dcp)]];
Now it becomes a bit murky. Why do you have type ins in your for loop if the ins are actually of type Item? You then cast them into a dictionary... This should generate a compiler error. Or you have another class called ins instead of Ins??
Anyway, if you stay with the Items you can just update the values with what you pass in your dictionary:
for (Item *item in matchingItems) {
item.newInsComp = [updatedNSD valueForKey:#"newInsComp"];
item.newDryComp = [updatedNSD valueForKey:#"newDryComp"];
item.updatedRow = [updatedNSD valueForKey:#"updatedRow"];
}
[self.managedObjectContext save:nil];
Done!
BTW you could make it even shorter by setting the entity name of the fetch request to "Item" and setting the following predicate:
[NSPredicate predicateWithFormat:#"project.projectID = %# && dcp = %#",
projectID, #(dcp)];
If you know your InProject, then updating your Ins related to that project is a matter of editing property values on your managed objects.
Why not use the predicate to get an NSManagedObject of the InProject, then pull the relationship off of that and edit the values?
NSManagedObjectContext *context = [self managedObjectContext];
if (!context) {
return;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"InsProject" inManagedObjectContext:context];
[fetchRequest setEntity:entity];
// Set the predicate on the Core Data fetch request instead
fetchRequest.predicate = [NSPredicate predicateWithFormat:#"ProjID==%#",projIDString];
NSError *error;
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
// We now have an array that has objects matching the projectIdString
// Might want to do some additional checks if you're only expecting zero or one objects
InsProject *aProject = [fetchedObjects lastObject];
// If we have no project, no point going any further
if ( !aProject ) return;
// On this NSManagedObject is an NSSet property with all related Ins objects
for ( Ins *anIns in aProject.ins ) {
// If our Ins item matches the passed dpc...
if ( [ins.dpc integerValue] == dpc ) {
// ...we have a match, edit properties
ins.dpc = #(dpc);
ins.newInsComp = [updatedNSD valueForKey:#"newInsComp"];
ins.newDryComp = [updatedNSD valueForKey:#"newDryComp"];
ins.updatedRow = [updatedNSD valueForKey:#"updatedRow"];
}
}
// These are managed objects, so saving the context saves all the changes
NSError *saveError;
[context save:&saveError];
if ( saveError ) {
NSLog(#"Save error: %#", [error localizedDescription]);
}
I'm trying to update an existing object in my Core Data stack,
The object is being retrieved and i can change the value, but when saving the context , nothing is being saved. also the hasChanges is NO and updatedObjects is empty.
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName: #"MyModel"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"(x == %#) AND (y == %#)", x, y];
request.returnsObjectsAsFaults = NO;
request.predicate = predicate;
NSArray *results = [self.managedObjectContext executeFetchRequest: request error: nil];
MyModel *model = results[0];
model.newvalue = "somenewvalue";
NSLog(#"%#", (self.managedObjectContext.hasChanges)?#"YES":#"NO"); // -> Shows NO
NSLog(#"%#", self.managedObjectContext.updatedObjects); // -> Shows empty array
[self saveContext]; // No error, seems to be working successfully but the updated objects is empty as well has "hasChanges", so something else is being missed here
This is a bit baffling and annoying. I would really appreciate any insights on this issue.
As suggested this was tried as well but didn't help
NSManagedObject *model = results[0];
[model setValue: #"somenewvalue" forKey: #"newvalue"];
Crazy answer but I can definitely imagine someone else making this error.
Inside my NSManagedObject instead of #dynamic for each property I had #synthesize. That was the issue.
This is a SyncEngine from an RW tutorial. I need help understanding how only UPDATED records from the web are fetched and processed into Core Data.
- (void)processJSONDataRecordsIntoCoreData {
NSManagedObjectContext *managedObjectContext = [[SDCoreDataController sharedInstance] backgroundManagedObjectContext];
// Iterate over all registered classes --- CHECK!
for (NSString *className in self.registeredClassesToSync) {
if (![self initialSyncComplete]) {
NSDictionary *JSONDictionary = [self JSONDictionaryForClassWithName:className];
NSArray *records = [JSONDictionary objectForKey:#"results"];
for (NSDictionary *record in records) {
[self newManagedObjectWithClassName:className forRecord:record];
}
} else {
NSArray *downloadedRecords = [self JSONDataRecordsForClass:className sortedByKey:#"objectId"];
if ([downloadedRecords lastObject]) {
NSArray *storedRecords = [self managedObjectsForClass:className sortedByKey:#"objectId" usingArrayOfIds:[downloadedRecords valueForKey:#"objectId"] inArrayOfIds:YES];
int currentIndex = 0;
//if dl count is < current index, there is an updated object dl from the web
for (NSDictionary *record in downloadedRecords) {
NSManagedObject *storedManagedObject = nil;
//Quick check to see if they indeed match, if they do, update the stored object with remote service objects
if ([storedRecords count] > currentIndex) {
storedManagedObject = [storedRecords objectAtIndex:currentIndex];
}
//Othwerwise its a new object and you need to create a new NSManagedObject to represent it in CDdb
if ([[storedManagedObject valueForKey:#"objectId"] isEqualToString:[record valueForKey:#"objectId"]]) {
[self updateManagedObject:[storedRecords objectAtIndex:currentIndex] withRecord:record];
} else {
[self newManagedObjectWithClassName:className forRecord:record];
}
currentIndex++;
}
}
}
// After all NSMO are created in your context, save it!
[managedObjectContext performBlockAndWait:^{
NSError *error = nil;
if (![managedObjectContext save:&error]) {
NSLog(#"Unable to save context for class %#", className);
}
}];
// Cleanup time
[self deleteJSONDataRecordsForClassWithName:className];
[self executeSyncCompletedOperations];
}
[self downloadDataForRegisteredObjects:NO];
}
From what I understand, on the first or initial sync, it fetches JSONDictionaryForClassWithName which reads the downloaded data from disk and creates a newManagedObjectWithClassName.
My confusion is in the update else block. downloadedRecords is populated from JSONDataRecordsForClass which simply calls JSONDictionaryForClassWithName. Then it checks to see if there is at least 1 object in that array. If there is it does this:
NSArray *storedRecords = [self managedObjectsForClass:className sortedByKey:#"objectId" usingArrayOfIds:[downloadedRecords valueForKey:#"objectId"] inArrayOfIds:YES];
This fetches all managedObjectsForClass:sortedByKey which is below:
- (NSArray *)managedObjectsForClass:(NSString *)className sortedByKey:(NSString *)key usingArrayOfIds:(NSArray *)idArray inArrayOfIds:(BOOL)inIds {
__block NSArray *results = nil;
NSManagedObjectContext *managedObjectContext = [[SDCoreDataController sharedInstance] backgroundManagedObjectContext];
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:className];
NSPredicate *predicate;
if (inIds) {
predicate = [NSPredicate predicateWithFormat:#"objectId IN %#", idArray];
} else {
predicate = [NSPredicate predicateWithFormat:#"NOT (objectId IN %#)", idArray];
}
[fetchRequest setPredicate:predicate];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:
[NSSortDescriptor sortDescriptorWithKey:#"objectId" ascending:YES]]];
[managedObjectContext performBlockAndWait:^{
NSError *error = nil;
results = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
}];
return results;
}
The next bit which compares the [storedRecords count] > currentIndex is confusing. Can someone please explain this? I think my confusion lies in what the managedObjectsForClass method does with the usingArraysOfIds & inArrayOfIds.
I would expect that at some point it gets the the updatedAt field from the downloaded records and compares it to the updatedAt field of the CoreData fetched records.
This function is processing the stored JSON. The actual remote fetching and updateAt checking happens in downloadDataForRegisteredObjects and mostRecentUpdatedAtDateForEntityWithName.
[storedRecords count] > currentIndex is a bit crazy. Although in defense of the original programmer, writing any decent syncengine will quickly make you go googoo. Basically he needs to work out which records are existing and which ones are new and update the local data store accordingly, that's all.
I had another look and this code is actually horribly broken. It will only works if either you have the same records both locally and remotely. Or if the new objects have an objectId that sort-wise comes after the last object the local store has. Which is not the case with Parse objectId's.
If you are testing with just one device this works because new objects will be inserted locally before being pushed to the server. Therefor you will always have the same amount of records. If additional records get inserted any other way, this code will do weird things.