I have a Entity with a column of type ID named "responsibleUsers". In this column I store an Array containing NSNumbers.
I want to fetch all objects of this entity, that match my current User. Therefore i create following predicate:
[NSPredicate predicateWithFormat: #"%# IN responsibleUsers",[NSNumber numberWithInteger: curUser.oID.integerValue] ]
whatever I try, my App crashes. Once with a EXC_BAD_ACESS, once with "unimplemented SQL generation for predicate nsnumber"
What is the correct way to query my entity?
The query you are trying assumes that you have two entities: the entity you querying (let's call it Group) and another one, perhaps called User, which is set up as a to-many relationship from Group called responsibleUsers. You would then be able to use the predicate you suggest:
[NSPredicate predicateWithFormat:#"%# IN responsibleUsers, aUser];
This would be the recommended use of Core Data object graphs.
In your setup, it seems you have an array of NSNumber set as a property rather than a relationship. Therefore you cannot use such a query. You simply have to retrieve the array and query the array.
BOOL containsResponsibleUser = NO;
for (NSNumber *n in aGroup.responsibleUsers) {
if ([n isEqualTo:[NSNumber numberWithInteger: curUser.oID.integerValue]])
containsResponsibleUser = YES;
}
If you are indeed querying something like a group of users, I would recommend the first approach. If you are querying some kind of user, I would suggest a BOOL property responsible as the most efficient solution.
Related
How do I sort my fetched results by a value that is returned by a method in a category of the entity I'm fetching?
In my category, I sum up several values from the entity's to-many relationship, then divide by the number of objects in the relationship, effectively creating an average that I return in my category method as a float value.
Here is my code:
In the Category.h
- (float)smallPenaltyAvg;
In the Category.m
- (float)smallPenaltyAvg{
float smallPenaltyAvg = 0;
for (Match *mtch in self.matches) {
smallPenaltyAvg += [mtch.penaltySmall floatValue];
}
if ([self.matches count] > 0) {
smallPenaltyAvg = (float)smallPenaltyAvg/(float)[self.matches count];
}
return smallPenaltyAvg;
}
And when I call it in the Core Data Table View Controller class that I created...
NSFetchRequest *poolRequest = [[NSFetchRequest alloc] initWithEntityName:#"Team"];
poolRequest.predicate = [NSPredicate predicateWithFormat:#"regionalIn.name = %#", _regionalToDisplay];
poolRequest.sortDescriptors = #[[NSSortDescriptor sortDescriptorWithKey:#"smallPenaltyAvg" ascending:YES]];
And I have the Category.h file imported on every file previously mentioned outside of the Category.h file itself.
It gives me the error of:
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'keypath smallPenaltyAvg not found in entity <NSSQLEntity Team id=5>
Am I not allowed to do this?
If I am, what am I doing wrong?
I do not think this has anything to do with the kind of persistent store.
The trick is to create an appropriate attribute in the managed object model, and mark it as Transient. Then override the getter of this attribute to do your calculations.
Now your fetch request should work as expected (although there are some caveats with fetched results controllers).
As for the SQLite problem, when you add the SQLite store with
- (NSPersistentStore *)addPersistentStoreWithType:(NSString *)storeType
configuration:(NSString *)configuration
URL:(NSURL *)storeURL
options:(NSDictionary *)options
error:(NSError **)error
just pass NSSQLiteStoreType as the storeType. The other options are binary and in-memory, so in this sense this is indeed the "default".
This is not possible when using a backing SQLite store.
My suggestion is you persist the average property, and maintain it yourself by overriding the Match setCategory: property and making the calculation there for every match added.
What I did to solve my problem was create a new attribute for every average or sum that I needed in the Team object from all of its Match objects' attributes and then created a method in the TeamCategory file that populated those averages and that method was called every time a Match object was inserted into the Team object. It took a while to do, but it works now. If there is a better solution, I'm still open for suggestions.
SCENARIO
I have two entities: Item and ListDetail (which contains prices for different lists for every item). This is absolutely needed and I can't provide a price attribute for the Item entity because every item can have more prices for different dynamic lists (retail, b2b ecc.).
The relationship is:
Item (lists) <------->> (item) ListDetail
The current active list in my app change dinamically, so let's say I have an integer variable with the current active list: _ACTIVE_LIST_CODE_. When I need a price for an item object I use an helper method on the Item class:
-(NSNumber*) getPrice {
NSSet *lists=[self.lists filteredSetUsingPredicate: [NSPredicate predicateWithFormat:#"listId == %d",_ACTIVE_LIST_CODE_]];
ListDetail *activeList=[[lists allObjects] objectAtIndex:0];
return activeList.price;
}
THE PROBLEM
I use a UITableView with NSFetchedResultController in order to select and show some items for different sections. Nothing special. I would like to order the fetchedObjects using the items price for the active list. If price was an attribute of Item I would added simply a sort descriptor to the fetch request like so:
[NSSortDescriptor sortDescriptorWithKey:#"price" ascending:YES];
But as said before this is not possible, price is a dynamic attribute.
If using transient properties was possible for sort descriptors, I would set a price transient properties calculated on fly using my helper method. Nothing to do.
Using a keypath in the descriptor like "lists.price" is not possible (or maybe I don't know how to do that), just because it's a to-many relationship and it's modeled with a NSSet.
I tried some workaround, without success:
1) observing _ACTIVE_LIST_CODE_ changes to set items price in a non-transient attribute.
2) after the fetch request, before presenting the table view, reorder a brand new array with fetched objects using the transient "price" property, iterate the orderdered array following an ascending integer index "i" and assigning this value to a non-transient property "order" for the Item entity. Using "order" for sort descriptor in the fetch request. (This approach is described here: Re-ordering NSFetchedResultsController)
Both of them works, but they slow down performance because I have thousands of items in the fetch results... Any idea?
How about fetching ListDetail instead? You could restrict and sort with the appropriate predicates and sort descriptors, exactly as you propose.
fetchRequest.predicate =
[NSPredicate predicateWithFormat:#"listID = %#", activeListCode];
fetchRequest.sortDescriptors =
#[[NSSortDescriptor sortDescriptorWithKey:#"price" ascending:YES]];
Now, to group by some attribute of item should be simple and efficient because it is a to-one relationship. Your fetched results controller's sectionNameKeyPath can be something like
#"item.category"
I have a block predicate that I carefully crafted only to discover you can't use them in Core Data.
NSPredicate *rootContactPredicate = [NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) {
BOOL isPersonAndRoot = ([[[evaluatedObject entity] name] isEqualToString:#"Person"] && [[(Person*)evaluatedObject accounts] count] == 0);
BOOL isAccountAndRoot = ([[[evaluatedObject entity] name] isEqualToString:#"Account"] && [(Account*)evaluatedObject root] == nil);
return isPersonAndRoot || isAccountAndRoot;
}];
So I need to convert this into a standard String format predicate, but I am unclear on how to check the entity type for the evaluated object. The Person and Account entities are subclasses of a Contact entity which is the type being evaluated in the fetch request. I'm hoping it will see the sub-types.
Check the entity like this:
[NSPredicate predicateWithFormat:#"self.entity = %#", Person.entity];
Swift 4.0 way of checking for entity type using the entity property of the NSManagedObject as per malhal's suggestion.
let entityDescription = NSEntityDescription.entity(forEntityName: "Account", in: managedObjectContext)!
return NSPredicate(format: "entity = %#", entityDescription)
It seems that now you can now simply compare the entity in a predicate, supplying the managed objects entity as the value:
"entity = %#"
Previously:
You can't. The reason is that the predicate will need to be converted so that it can be run on the underlying data store (presumably SQLite). The SQLite database doesn't have any data on the type of the element, it only knows about the keys and values of the objects.
Depending on what you're trying to do, you'll either need to run a single fetch request against the keys known in the super entity. Or you'd need to have 2 fetch requests, separately executed and then combine the 2 result sets.
Suppose a Manager has a to-many relationship with Employee objects. Given a reference to a Manager object (i.e. NSManagedObject *manager), how do I get a reference to "the Employee with the lowest salary among all of those whose salaries exceed 10000"?
I can think of two possible approaches:
Approach 1: constructing an NSFetchRequest and specifying the Manager wanted with the object ID of the Manager in question.
Approach 2: some kind of key-value coding expression on Manager, e.g. [manager valueForKeyPath:#"..."] (with some use of NSPredicate?)
I'm inclined towards Approach 2 if there's a plausible solution. Please enlighten me.
Of course, you can just apply a predicate and sort descriptor to the set returned by the relationship. Easy, and pretty quick if the set is relatively small (because it is done in memory, all the objects will have to be fetched). You may want to do that batch fetch up front to limit the number of times you do I/O.
Depending on the size of the database and the number of employees under the manager (and the indexing), you may want to do it all at the database level...
// We want "Employee" objects
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:#"Employee"];
// Assuming the "inverse" relationship from employee-to-manager is "manager"...
// We want all employees that have "our" manager, and a salary > 10000
fetchRequest.predicate = [NSPredicate predicateWithFormat:#"(manager == %#) AND (salary > 10000", manager];
// Sort all the matches by salary, little-to-big
fetchRequest.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:#"salary" ascending:YES]];
// Limit the returned set to 1 object, which will be the smallest
fetchRequest.fetchLimit = 1;
This will perform the entire query at the database level, and only return 1 object.
As always, performance issues are usually highly dependent on your model layout, and the options used for specifying the model and its relationships.
You can filter your array of Employee relationship to get the one you want.
1) First, get all the Employee with salaries over 10000:
NSArray *filtered = [manager.employees filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:#"(salary > 10000)"]];
2)Then sort it in descending order
NSSortDescriptor* sortOrder = [NSSortDescriptor sortDescriptorWithKey: #"salary" ascending: NO];
NSArray *sortedAndFiltered = [filtered sortedArrayUsingDescriptors: [NSArray arrayWithObject: sortOrder]];
3)Then just get your employee
[sortedAndFiltered lastObject];
Is there any way I can validate a value updated in a Core Data entity's property against values of the property in other entities in the collection?
At the moment I create an entity with some default values, add it to arrangedObjects, then get the user to modify the various property values. However, I would like to check a particular property and make sure there're no other entities in the array with the same value for that property. What's the best way to do this?
Many thanks,
Dany.
Manually checking is only a few lines of code with a fast enumeration loop:
BOOL unique = YES;
for (NSManagedObject *obj in collection) {
if (obj.property == value) {
unique = NO;
break;
}
}