I have a table populated with coredata (all staff), but I need another table with only staff from one center (there are 3 centers),
the center is an attribute in my entity,
so how can I show this list? (populate table with staff from x center?) do I use NSPredicate?
thanks
I give you a function which returns you array according to center type what you need to a column called center in your entity.
and in folloeing function you need to pass center name like #"x" or #"y".And function give you what you want.
- (NSMutableArray *)getRecordsByCenter:(NSString *)cen{
NSMutableArray *fetchResults;
NSString *entityName=#"YourEntity";
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:globalManagedObjectContext];
[fetchRequest setEntity:entity];
fetchResults = [NSMutableArray arrayWithArray:[globalManagedObjectContext executeFetchRequest:fetchRequest error:nil]];
[fetchResults filterUsingPredicate:[NSPredicate predicateWithFormat:#"center == %#",cen]] ;
[fetchRequest release];
return fetchResults;
}
Related
In my data model, I have:
Activity(name, sponsor, Location*) // one activity may have many Locations
Location(name, street, suburb, state, postcode)
And I need a way to get activities with specified location name, for example, user wants to know all activities in "ICT Building", so how do I construct the predicate for the query?
Something like:
"Location.name == ICT Building" ?
Thanks!
Use this where managedObjectContext is your context:
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
entityForName:#"Activity" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
NSString *locationName = #"ICT Building";
NSPredicate *pred = [NSPredicate predicateWithFormat:#"Location.name CONTAINS %#", locationName];
[fetchRequest setPredicate:pred];
NSError *error = nil;
NSArray *objects = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
This will return an array with managed objects where the name is ICT Building.
I finally figured it out. Change
#"Location.name == %#"
to
#"Location.name CONTAINS %#"
in #CoreCode's answer.
How do I fetch all child entities of a parent?
I have a table populated by a parent entity in Core Data. When the user touches a cell I intend to show another table with all children of that parent.
How does the NSFetchRequest look like for this please?
Edit:
model is like this:
student>>dates [one to many, one student have many days]
So I want all dates for any given student (selected by touching in student table cell for that student), then populate dates table with dates for that student.
Thanks!
Assuming that the entity and the class names are Student and Date, and the reverse relationship for Date->Student is called student,
Student *aStudent = ...;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity: [NSEntityDescription entityForName: #"Date" inManagedObjectContext: [aStudent managedObjectContext]]];
[fetchRequest setPredicate: [NSPredicate predicateWithFormat: #"student == %#", aStudent]];
You don't need a separate fetch request for this. All of the objects from the to-many relationship (don't call them child entities, that is misleading and incorrect) are available by accessing the relationship from the student object - something like student.dates. This gives you an NSSet, you can sort it and turn it to an array if you need to.
Within your first table delegate, when you touch a specific cell, I'll inject the specific parent property to the second table controller. For example:
SecondController secondController = ... // alloc-init
secondController.studentToGrab = ...
where SecondController declaration has a studentToGrab property like the following:
#property (nonatomic, retain) Student* studentToGrab; // use strong with ARC, if non-ARC remember to release it
and in definition synthesize it.
Then in your second controller, within viewDidLoad method you could do:
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"YourNameEntityForDate" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setFetchBatchSize:20];
NSPredicate* predicate = [NSPredicate predicateWithFormat:#"student == %#", studentToGrab];
[fetchRequest setPredicate:predicate];
// you can also use a sortdescriptors to order dates...
NSError *error = nil;
NSArray *resultArray = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
if (error != nil) {
NSLog(#"Error: %#", [error localizedDescription]);
abort();
}
// use resultArray to populate something...
A remark when you deal with table you could also use NSFetchedResultController class. It has advantages when used for displaying data in tables.
If you have custom classes, you could traverse the generated relationship (return [student dates]). That will get you an unordered NSSet on iOS4, or, you can do it with a fetch request (note I use ARC so no releases/autoreleases here):
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Date"
inManagedObjectContext:moc];
[fetchRequest setEntity:entity];
NSMutableArray *predicates = [NSMutableArray arrayWithCapacity:3];
[predicates addObject:[NSPredicate predicateWithFormat:#"student == %#", aStudent]];
// You might add other predicates
[fetchRequest setPredicate:[NSCompoundPredicate andPredicateWithSubpredicates:predicates]];
// and if you want sorted results (why not, get the database to do it for you)
// sort by date to the top
NSArray *sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:#"dateAdded" ascending:NO]];
}
[fetchRequest setSortDescriptors:sortDescriptors];
NSError *error = nil;
NSArray *sorted = [moc executeFetchRequest:fetchRequest error:&error];
if (error) {
// Handle the error, do something useful
}
return sorted;
I have created a Users class based on NSManagedObject with following attributes (id,name,age etc).
I am using the core data model but i am not sure how to do the follwing...
Now i would like to know How can i get the user detail based on user id.
example: select * from users where id = 1
please help me out.
You should use NSPredicate class for executing SQL commands. The code:
NSManagedObjectContext *context = self.managedObjectContext; // specify your MOC object
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"users" inManagedObjectContext:context]; // specify your entity (table)
NSPredicate *predicate = [NSPredicate predicatewithFormat:#"id == %d",yourID]; // specify your condition (predicate)
[fetchRequest setEntity:entity];
[fetchRequest setPredicate:predicate];
NSError *error = nil;
NSArray *array = [context executeFetchRequest:fetchRequest error:&error]; // execute
[entity release];
[predicate release];
[fetchRequest release];
if (array == nil) {
// Error: no objects returned
} else {
// Success: do whatever you want
}
Step 1: Alloc/init NSFetchRequest
You need to alloc/init a NSFetchRequest object if you want to execute queries.
Step 2: Select entity
If you want to specify select * from users ..., you should use NSEntityDescription:
NSEntityDescription *entity = [NSEntityDescription entityForName:#"users" inManagedObjectContext:context];
At the end you need to 'attach' your entity description to your NSFetchRequest object via:
[fetchRequest setEntity:entity];
Step 3: Condition
If you want to have a condition (e.g. ... where id = 1), you have to implement NSPredicate.
NSPredicate *predicate = [NSPredicate predicatewithFormat:#"id == %d",yourID];
yourID must be a number (e.g. 1, 2, 7 or 46).
And, again:
[fetchRequest setPredicate:predicate];
Step 4: Let's execute it!
NSArray *array = [context executeFetchRequest:fetchRequest error:&error];
All the records that meet the conditions will be returned as array of NSManagedObjects.
Step 5: Release objects
[entity release];
[predicate release];
[fetchRequest release];
Step 6: Do something
If there are no objects that meet the conditions, array object will be nil. You can check it and deal with the error via:
if (array == nil)
Check out Core Data Programming Guide for more info. :)
I haven't seen any other questions quite like this on here, but I'm hoping someone has some insight. I'm just starting to learn Core Data.
Basically, I have two methods and I want to choose which one to call with an if/else statement based on whether or not the "Contacts" table contains any records. Is there a way using core data to check if there are any records in a table?
The best way I've found so far is to set the fetchLimit to 1 and then check to see if anything returns.
[request setFetchLimit:1];
But I keep thinking there has to be a better/easier way. Anyone know or have a good reference I can look at?
Thanks a ton!
Yes, definitely there is a better method. Setup a fetch request as usual, but, instead of actually executing it, simply ask for the number of objects it would have returned if it had been passed to executeFetchRequest:error:
This can be done using
- (NSUInteger)countForFetchRequest:(NSFetchRequest *)request error:(NSError **)error;
Something like this:
- (int) numberOfContacts{
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSManagedObjectContext *managedObjectContext = yourManagedObjectContext;
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Contacts" inManagedObjectContext:managedObjectContext];
[request setEntity:entity];
NSError *error = nil;
NSUInteger count = [managedObjectContext countForFetchRequest:request error:&error];
[request release];
if (!error){
return count;
}
else
return -1;
}
It's not necessarily any better or easier, but you can look for a specific record and then create it if it doesn't exist like this:
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Contact"
inManagedObjectContext:[self managedObjectContext]];
[fetchRequest setEntity:entity];
NSError *error;
// Filter based on a predicate
[fetchRequest setPredicate:
[NSPredicate predicateWithFormat:#"identifier == %#", #"1"]];
NSManagedObject *contact = [[managedObjectContext
executeFetchRequest:fetchRequest error:&error] lastObject];
// If the contact was not found
if (!contact)
{
// Create the contact
contact = [NSEntityDescription insertNewObjectForEntityForName:#"Contact"
inManagedObjectContext:managedObjectContext];
[contact setValue:[NSNumber numberWithInt:1] forKey:#"identifier"];
[managedObjectContext save:nil];
}
Marcus Zarra posted some code that demonstrates this in a feed reader app. Marcus is the Core Data master.
can anyone guide me how to create a fetch request that will query an entity and returns any properties that qualify my criteria.
Here's what I have. I have an entity that has 35 properties, all are in types of float.
What I need was to see all properties of the entity which values was <= zero.
I know how to return the values of the properties but not how to return the name of the property.
Thanks,
CoreData doesn't return properties. It returns entities, which then have properties. In any case, you'd have to do something like this:
(The following is pseudo-code done from memory. Treat it accordingly.)
NSString *query = #"(property1 <= 0) && (property2 <= 0)";
NSPredicate *predicate = [NSPredicate predicateWithFormat:query];
NSEntityDescription *entity = [NSEntityDescription entityDescriptionForName:#"Entity" inManagedObjectContext:context];
NSFetchRequest *fetch = [[NSFetchRequest alloc] init];
[fetch setEntity:entity];
[fetch setPredicate:predicate];
NSError *error = nil;
NSArray *entities = [context executeFetchRequest:fetch error:&error];
// Let's just assume we got one
NSManagedObject *obj = [entities objectAtIndex:0];
float value = [obj valueForKey:#"property1"];
Or something like that.