I'm importing data from an API that's giving me JSON data. Each object that gets added into core data has an attribute named "id". I want to be able to check if the id is already in core data after the initial import. I have written this code out for it so far:
- (void)mergeData: (NSString *)entityDescription {
NSPredicate *pred = [NSPredicate predicateWithFormat:#"id == %#", _bank.id]; // Bank is the entity
// id is the key from the raw JSON
NSFetchRequest *fetch = [[NSFetchRequest alloc] init];
NSError *error = nil;
[fetch setEntity:[NSEntityDescription entityForName:#"Banks" inManagedObjectContext:self.managedObjectContext]];
[fetch setPredicate:pred];
NSArray *items = [self.managedObjectContext executeFetchRequest:fetch error:&error];
for (NSManagedObject *object in items) {
// Loop over all the items and check to see if the ids match with any ids from the feed
// if any of them don't match, add the new ids
if (!match) {
// add new object
// I'm not sure how to implement this part
}
}
But I know it's not complete and I'm not sure how to implement the rest of the code for this part. Any help would be appreciated.
Related
I have core data entity called "Songs" which contains details of different songs details. One of the attribute of this entity is "Language". I want to fetch all songs with Language Spanish. But if number of songs with Spanish is zero, then it should fetch all songs with default language, thats english. Is this possible through single NSPredicate if I know default language and needed language.
You can do it this way.
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Songs" inManagedObjectContext:managedObjectContext];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
//here strLanguage is string with the name of selected language
NSPredicate * predicate = [NSPredicate predicateWithFormat:#"Language == %#",strLanguage];
[request setPredicate:predicate];
[request setEntity:entity];
NSMutableArray* mutableFetchCategory = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];
if ([mutableFetchCategory count] > 0)
{
for (NSManagedObject *info in mutableFetchCategory)
{
NSLog(#"%#",info);
//Extract data from each "info" object and store it in an array and display it in tableview
}
}
else
{
// Repeat the same code [or u can use functions for reusability] with language "English".
}
You can also refer this link
I have a very simple fetch request that i want to execute. One of my entities has an attribute called smartCollectionIds and it is of type transformable. I use this attribute to store an NSArray of simple strings. In my code i use an NSfetchedResultsController to populate a tableview. The predicate im using is as follows:
predicate=[NSPredicate predicateWithFormat:#"smartCollectionIds!=nil && (%# IN smartCollectionIds)",#"87F173A5-863D-4ECE-9673-A61D8F1E01FC-6285-000009A9CBAF3290"];
however this causes a crash, specifically at the pint when i perform a fetch. However, if i first use a fetch to load all my objects into an array, and then filter them out with the above predicate, the app does not crash, and i get my results as expected. So basically
THIS CODE BELOW DOES NOT WORK
-(void) tryTO
{
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Tweetary" inManagedObjectContext: [[ChubbyEyetwitterEngine sharedInstance] getManagedObjectContextForUse]];
NSPredicate *predicate;
predicate=[NSPredicate predicateWithFormat:#"smartCollectionIds!=nil && (%# IN smartCollectionIds)",#"87F173A5-863D-4ECE-9673-A61D8F1E01FC-6285-000009A9CBAF3290"];
NSSortDescriptor *secondarySortKey = [[[NSSortDescriptor alloc] initWithKey:#"created_at" ascending:FALSE] autorelease];
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease] ;
[request setEntity:entity];
[request setPredicate:predicate];
[request setSortDescriptors:[NSArray arrayWithObjects:
secondarySortKey
,nil]];
[request setFetchLimit:30]; //30
NSError *error;
NSArray *results = [[[ChubbyEyetwitterEngine sharedInstance] getManagedObjectContextForUse] executeFetchRequest:request error:&error];
if (error != nil)
{
NSLog(#"Results are %d",[results count]);
}else{
NSLog(#"findAllObjectsInContext error %#",error);
}
}
BUT THIS WORKS
NSArray *tweets = [Tweetary findAllObjectsInContext:[[ChubbyEyetwitterEngine sharedInstance] getManagedObjectContextForUse]];
NSLog(#"Before filter count is %d",[tweets count]);
predicate=[NSPredicate predicateWithFormat:#"smartCollectionIds!=nil && (%# IN smartCollectionIds)",#"87F173A5-863D-4ECE-9673-A61D8F1E01FC-6285-000009A9CBAF3290"];
predicate=[NSPredicate predicateWithFormat:#"smartCollectionIds!=nil && (%# IN smartCollectionIds)",#"87F173A5-863D-4ECE-9673-A61D8F1E01FC-6285-000009A9CBAF3290"];
NSArray *bNames = [tweets filteredArrayUsingPredicate:predicate];
NSLog(#"FINAL Results %d",[bNames count]);
+ (NSArray *)findAllObjectsInContext:(NSManagedObjectContext *)context;
{
#synchronized(self){
NSEntityDescription *entity = [self entityDescriptionInContext:context];
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:entity];
NSError *error = nil;
NSArray *results = [context executeFetchRequest:request error:&error];
if (error != nil)
{
//handle errors
//NSLog(#"findAllObjectsInContext error %#",error);
}
return results;
}
}
In a nutshell, i need my fetch predicate to work when using NSfetchedResultsController instead of first loading up my objects into an array, and then applying my filter predicate. Can anyone point me in the right direction/ figure out why the predicate works only after i load my unfiltered data set into an array?
A Core Data fetch request with a predicate is translated to a SQLite query and executed
on the SQLite level. A transformable array is stored as some blob in the SQLite database,
therefore treating it as array in a fetch request does not work.
If you fetch the elements first, the blob is transformed back to an array
when the property is accessed. Therefore filtering the array of fetched objects works as expected.
I don't think there is any workaround. You cannot filter on transformable properties
in a fetch request.
I'm trying to add unique values into my sqlite DB.
I've tried to create unique attribute into the .xcdatamodeld but I didn't succeed.
This part of code adds all terminaison in the Table F016Terminaison. How can I add only unique terminaison values?
for (NSString *terminaison in [[verbe objectForKey:temps] objectForKey:#"terminaison"])
{
F016Terminaison *newTerminaison = [NSEntityDescription insertNewObjectForEntityForName:#"F016Terminaison" inManagedObjectContext:self.managedObjectContext];
newTerminaison.name = terminaison;
}
Each call to insertNewObjectForEntityForName creates a new object and inserts it into
the managed object context.
If you want only unique values, you have to check first if an object with that value
already exists. That is done with an NSFetchRequest with a predicate like
[NSPredicate predicateWithFormat:#"name == %#", terminaison];
If you have to insert many values, then it is more effective to fetch all objects having
values from the new list first instead of many fetch requests.
Compare "Implementing Find-or-Create Efficiently" in the "Core Data Programming Guide".
You need to do a fetch to find existing instances of an object, then add it if it doesn't exist.
eg:
// assumes your object has a "uniqueAttribute" and you supply a uniqueValue to test
NSPredicate * predicate = [NSPredicate predicateWithFormat:#"uniqueAttribute == %#", uniqueValue];
NSFetchRequest * fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setPredicate:predicate];
[fetchRequest setFetchLimit:1];
NSError * error = nil;
NSArray * results = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
if ([results count] == 1) {
id existingObject = [results objectAtIndex:0];
// do something with existing object
}
else if (results) {
// create a new object
}
else {
NSLog(#"executeFetchRequest returned error: %# (userInfo: %#)", [error localizedDescription], [error userInfo]);
}
I currently have a table view that displays all the contents of the database Entity: ExData.
ExData has an attribute tag of string type.
What my problem is that i would like to display the contents of the ExData in the table view but only the entries that have a tag set of 2 for example.
The tag is to be sent from the previous view controller but this can be sorted out later as firstly i would just like to hard code only one tag value entries being displayed
ExDatasArray is a mutable Array.
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:#"ExData"];
self.ExdatasArray = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
Above is how the data from ExData is being fetched...
To fetch specific data, you add a predicate to the fetch request:
NSString *theTag = ...
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"tag == %#", theTag];
[fetchRequest setPredicate:predicate];
Remark: If you are displaying the result set in a table view, you might also consider to
use a NSFetchedResultsController.
If I understand your question correctly, you are trying to limit the results of the fetchRequest. Use an NSPredicate to specify the query and if desired an NSSortDescriptor to sort it. Below I assume that your tag attribute is named tag, and that searchTagValue has been set appropriately.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:#"ExData"];
fetchRequest.predicate = [NSPredicate predicateWithFormat:#"tag == %#", searchTagValue];
fetchRequest.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:#"tag" ascending:YES]];
NSError *error;
NSArray *results = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
if (!result) {
// handle error
}
else {
self.ExdatasArray = [results mutableCopy];
}
I m trying to update some records in Core Data. I m adopting following steps to get it done
Fetch function with predicate retrieves the records from the Core Data
Store the result set in a Object Array
Loops through the array and update each record
Call save context
I m running into two problems
After Initial run i get < fault > in the log
I m not sure whether the save context will actually save the object
My code:
- (void)fetchExpenses {
// Define our table/entity to use
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Expense" inManagedObjectContext:managedObjectContext];
// Setup the fetch request
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entity];
// Define how we will sort the records
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"timestamp" ascending:NO];
NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor];
[request setSortDescriptors:sortDescriptors];
[sortDescriptor release];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"publishTimestamp == nil"];
[request setPredicate:predicate];
// Fetch the records and handle an error
NSError *error;
NSMutableArray *mutableFetchResults = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];
if (!mutableFetchResults) {
// Handle the error.
// This is a serious error and should advise the user to restart the application
}
// Save our fetched data to an array
[self setExpenseArray: mutableFetchResults];
[mutableFetchResults release];
[request release];
}
- (void) save: {
[self fetchExpenses];
int i = 1;
int max = [expenseArray count];
for(i=1; i<=max; i++) {
// Get the expense selected.
Expense *expense = [expenseArray objectAtIndex: i];
// Do your updates here
[expense setTimestamp:2]
}
}
The fault you are seeing in the log doesn't indicate an error but means that the managed object is not fully loaded into memory but is instead represented by a fault object. This is normal behavior. When you try to access or change an object attribute the full object will be "faulted" or read-in to memory. It's a confusing old-fashion database terminology that dates back to 1960s.
Your code does not save any objects. Changes to managed objects in memory will not be persisted until you call a save on the managed object context.
You also do not want to use a mutable copy like this:
NSMutableArray *mutableFetchResults = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];
… because it waste memory and can lead to duplicate managed objects. There was some code in Apple docs that got this started but its erroneous. Instead, just use:
NSArray *fetchResults=[managedObjectContext executeFetchRequest:request error:&error];
… which will return an autoreleased array of the managed objects matching the fetch.