I have two entities. Client and Project. A Client has many Projects, but a Project can only be assigned to one Client. This has been designed with the datamodel.
Client entity has attribute clientName and relationship to-many projects
Project entity has attribute projectName and relationship to-one client
I want to retrieve all Clients from my ManagedObjectContext where the Clients are sorted by clientName ascending and then have the Projects for that Client by projectName ascending.
This is my current code, where I KNOW it is wrong since there is no way for Client entity to sort by the projectName:
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Client" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
// Creating the sort descriptors array.
NSSortDescriptor *clientSort = [[NSSortDescriptor alloc] initWithKey:#"clientName" ascending:YES];
// this next row is super wrong
NSSortDescriptor *projectSort = [[NSSortDescriptor alloc] initWithKey:#"projectName" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:clientSort. projectSort, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
NSError *error;
// Assign to NSArray of ViewController
clientArray = [[managedObjectContext executeFetchRequest:fetchRequest error:&error] mutableCopy];
After this has been assigned to clientArray, I want to go to another method and ask for the Projects and have them in ascending order. Example:
Client *temp = (Client *)[clientArray objectAtIndex:selectedClient];
NSArray *projectsArray = [temp.projects allObjects];
Project *project = [projectsArray objectAtIndex:selectedProject];
return project.projectName;
I saw an implementation where they got the Clients and then sorted the projects manually... But this is kind of expensive and I'm hoping there are functions to do this when the Context gets queried.
You could add your own custom property to Client
#interface Client : NSManagedObject {
}
// ... other properties
#property (nonatomic,readonly) NSArray* orderedProjects;
#end
#implementation
// ... #dynamic etc
#dynamic orderedProjects;
- (NSArray*)orderedProjects {
NSArray* sort = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:#"projectName" ascending:YES]]
return [[self.projects allObjects] sortedArrayUsingDescriptors:sort];
}
#end
Now you just have to fetch all clients, which now each have sorted projects. Performance wise I'm not sure this is the best approach but it makes for cleaner code I think.
Try using a key path for the sort, such as project.projectName in the sort descriptor. This is a bit of a shot in the dark because I haven't tried this myself so don't kill me if I'm wrong.
Related
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've got a column with integer values in CoreData. While retrieving results from it, I want the column values to be subtracted with a number.
Something like: columnValue - someNumber (this number is entered by user)
I know I may have to use NSPredicate for this, but am unaware if there's a function or syntax for it.
The alternate right now I have is to iterate all column values and subtract with 'someNumber'. But I think there should be a better and efficient way to do this.
Edit: Code from #salo.dm 's answer
- (NSDictionary *)myFetchResults {
//Predicate works fine
NSPredicate *predicate = [NSCompoundPredicate andPredicateWithSubpredicates:[NSArray arrayWithObjects:pred1, pred2, nil]];
/*Sort Descroptor - Sorting by 4 columns*/
NSSortDescriptor *sortDesc1 = [NSSortDescriptor sortDescriptorWithKey:#"Column1" ascending:YES];
NSSortDescriptor *sortDesc2 = [NSSortDescriptor sortDescriptorWithKey:#"Column2" ascending:YES];
NSSortDescriptor *sortDesc3 = [NSSortDescriptor sortDescriptorWithKey:#"Column3" ascending:YES];
NSSortDescriptor *sortDesc4 = [NSSortDescriptor sortDescriptorWithKey:#"Column4" ascending:YES];
/*Get Data*/
MyAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
NSManagedObjectContext *context = [appDelegate managedObjectContext];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"TableName" inManagedObjectContext:context];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:entity];
[fetchRequest setPredicate:predicate];
[fetchRequest setSortDescriptors:[NSArray arrayWithObjects:sortDesc1, sortDesc2, sortDesc3, sortDesc4, nil]];
NSArray *listData = [context executeFetchRequest:fetchRequest error:nil];
/*Create subtract expression*/
NSExpressionDescription *subExp1 = [[NSExpressionDescription alloc] init];
[subExpLatitude setName:#"subtraction1"];
[subExpLatitude setExpression:[NSExpression expressionForFunction:#"from:subtract:"
arguments:[NSArray arrayWithObjects:
[NSExpression expressionForKeyPath:#"Column3"],
[NSExpression expressionForConstantValue:[NSNumber numberWithDouble:someNumber1]],
nil]]];
[subExp1 setExpressionResultType:NSDoubleAttributeType];
NSExpressionDescription *subExp2 = [[NSExpressionDescription alloc] init];
[subExpLongitude setName:#"subtraction2"];
[subExpLongitude setExpression:[NSExpression expressionForFunction:#"from:subtract:"
arguments:[NSArray arrayWithObjects:
[NSExpression expressionForKeyPath:#"Column4"],
[NSExpression expressionForConstantValue:[NSNumber numberWithDouble:someNumber2]],
nil]]];
[subExp2 setExpressionResultType:NSDoubleAttributeType];
/*Get difference data*/
[fetchRequest setResultType:NSDictionaryResultType];
[fetchRequest setPropertiesToFetch:[NSArray arrayWithObjects:subExp1, subExp2, nil]];
NSArray *listDifference = [context executeFetchRequest:fetchRequest error:nil];
NSLog(#"Subtraction 1: %#", [[listDifference objectAtIndex:0] objectForKey:#"subtraction1"]);
NSLog(#"Subtraction 2: %#", [[listDifference objectAtIndex:0] objectForKey:#"subtraction2"]);
NSMutableDictionary *dictResult;
[dictResult setObject:listData forKey:#"Data"]
[dictResult setObject:listDifference forKey:#"Difference"]
return dictResult;
}
Edit: Get coredata object
This doesn't work.
NSExpressionDescription *expEntity = [[NSExpressionDescription alloc] init];
[expEntity setName:#"TableNameEntity"];
[expEntity setExpression:[NSExpression expressionForKeyPath:#"objectID"]]; //Searches for a column for the name specified
[expEntity setExpressionResultType:NSObjectIDAttributeType];}
Had to change it to below to get it working (Assuming this is the correct way)
NSExpressionDescription *expEntity = [[NSExpressionDescription alloc] init];
[expEntity setName:#"TableNameEntity"];
[expEntity setExpression:[NSExpression expressionForEvaluatedObject]];
[expEntity setExpressionResultType:NSObjectIDAttributeType];
I added expEntity to the setPropertiesToFetch list. Now I get two values in the dictionary.
{
TableNameEntity = "0x5e22120 <x-coredata://1A659A52-9321-4ACD-992B-04F20E7BDCED/TableNameEntity/p1640>";
subtractionValue = "-24.13";
}
When I try to retrieve and access TableNameEntity from the dictionary, the app crashes.
TableNameEntity *tableEntity = (TableNameEntity *)[dict objectForKey:#"TableNameEntity"];
tableEntity.column1 //This is not the exact code. But this operation crashes with error
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[_NSObjectID_48_0 column1]: unrecognized selector sent to instance 0x5e22120'
Here if you notice, the value for key TableNameEntity is contained in quotes, so I guess its being returned as a string.
See if you can correct what I've done wrong.
I've tried an alternate to get columns values in the dictionary. Here it is (this works fine). But I guess its not a good approach.
[fetchRequest setPropertiesToFetch:[NSArray arrayWithObjects:subExp1, #"column1", #"column2", ... #"columnN" nil]];
You could make the calculation in a fetch request as follows:
- (NSArray *)myFetchResults
{
NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [NSEntityDescription entityForName:#"myEntity" inManagedObjectContext:myContext];
request.resultType = NSDictionaryResultType;
NSExpressionDescription *subExDescr = [[NSExpressionDescription alloc] init];
[subExDescr setName:#"subtraction"];
[subExDescr setExpression:[NSExpression expressionForFunction:#"subtract:from:"
arguments:[NSArray arrayWithObjects:
[NSExpression expressionForConstantValue:[NSNumber numberWithInt:someNumber]],
[NSExpression expressionForKeyPath:#"myAttribute"],
nil]]];
[subExDescr setExpressionResultType:NSInteger64AttributeType];
request.propertiesToFetch = [NSArray arrayWithObject:subExDescr, nil];
NSError *err = nil;
NSArray *results = [self.moContext executeFetchRequest:request error:&err];
[request release];
[err release];
return results;
}
The fetch results will be an array of dictionaries. You can access the result for the nth value in the column as follows:
NSArray *results = [self myFetchResults];
NSDictionary *nthDict = [results objectAtIndex:n];
NSInteger nthValue = [nthDict objectForKey:#"subtraction"];
Note that this code is untested. As is, I believe it will operate on all items in the column. If you want to operate only on selected items, you can add a predicate to select the items you want to operate on.
You could also look up the documentation for NSExpression and build all sorts of different operations. The class is a bit dense, but the Apple documentation has some snippets of code that help to understand how to use it. And I hope the above example illustrates how to incorporate it into a fetch request.
EDIT: CORRECTION
The entity, of course, has to be specified in the fetch request. I had initially left that out, but have now corrected the code.
EDIT: RESPONSE TO COMMENT
I'm not sure I understand what you're asking, but this may be it. You can create expression descriptions as follows:
NSExpressionDescription *expLatitude = [[NSExpressionDescription alloc] init];
[expLatitude setName:#"latitude"];
[expLatitude setExpression:[NSExpression expressionForKeyPath:#"Column3"]];
[expLatitude setExpressionResultType:NSDoubleAttributeType];
NSExpressionDescription *expEntity = [[NSExpressionDescription alloc] init];
[expEntity setName:#"TableNameEntity"];
[expEntity setExpression:[NSExpression expressionForKeyPath:#"objectID"]];
[expEntity setExpressionResultType:NSObjectIDAttributeType];}
Then, you add them to the propertiesToFetch array, as two more objects. Each dictionary in the fetch results will now have the latitude, the subtraction resulting from that same latitude, and the corresponding objectID of the entity that contained that latitude. The dictionaries will be ordered in the results array according to your sort descriptors. (I haven't tried the objectID expression, but I think it should work fine.)
Basically, your results are ordered in the exact same order as a traditional fetch request with the same predicate and the same sort descriptors, that is, for a fetch request with the default result type NSManagedObjectResultType.
I hope this answers your question. If not, don't hesitate to ask again. But, I may take a while to answer because it's sleep time for me now.
EDIT: RESPONSE TO 'GET COREDATA OBJECT'
Good catch on finding the correct expression to get the object ID! (Seeing it, the expression I offered for this now looks obviously wrong.)
As to the exception you're getting, it makes sense. The value returned in the fetch results is not the managed object itself, it's only the managed object's ID. To access the managed object, I think the following should work:
NSManagedObjectID *myObjectID = [dict objectForKey:#"TableNameEntity"];
TableNameEntity *tableEntity = (TableNameEntity *)[context objectWithID:myObjectID];
tableEntity.column1
The context above is the NSManagedObjectContext.
However, I think I prefer your final solution. I didn't know you could combine NSExpressionDescriptions with properties in the propertiesToFetch array. Good to know!
More importantly, it may be faster to get all the properties you need in the fetch than to get only the objectID from the fetch and get the properties later. Getting the objectID generally does not fire the fault for the entity. I believe the fault will be fired later, when you access the properties. It will fire once, when accessing the first property, or multiple times, once for each property. (I'm not sure which.) [For an explanation of faulting, see Firing Faults.]
My recommendation is that including all the properties you need in propertiesToFetch is the best approach. (You may try getting the objectID, if you prefer. But, if you find it's slow, you can go back to getting all the properties in the fetch.)
Fetch requests and expressions are poorly documented. You have to play with them a bit to get the syntax right. You seem to be doing very well.
I have implement a UItable with data sourced via Core Data. The table works fine and presents the data correctly, drills down.. etc.
However, it has the following problem: it presents the content data in a different order every time. I would like it at least to appear consistently or even better alphabetically.
Any ideas on why this might be happening or a specific property or method I should be reviewing in the docuemntation?
Help much appreciated
You need to set an NSSortDescriptor on your NSFetchRequest
NSSortDescriptor *sortDescriptorName = [[NSSortDescriptor alloc] initWithKey:#"name" ascending:YES selector:#selector(caseInsensitiveCompare:)];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sortDescriptorName]];
Then create your NSFetchedResultsController with the fetchRequest object.
This would cause your list to appear sorted alphabetically using the property "name" and ignore case while sorting.
You can simply add a sort descriptor to the request. In this example, the data object has a numeric column for "sortOrder", but you could sort on most anything.
- (NSMutableArray *)loadData {
NSManagedObjectContext *context = [self managedObjectContext];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"NameOfEntity" inManagedObjectContext:context];
[request setEntity:entity];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"sortOrder" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[request setSortDescriptors:sortDescriptors];
[sortDescriptors release];
[sortDescriptor release];
NSError *error = nil;
NSMutableArray *mutableFetchResults = [[context executeFetchRequest:request error:&error] mutableCopy];
if (mutableFetchResults == nil) {
// Handle the error.
}
[request release];
return [mutableFetchResults autorelease];
}
I have not done much with CoreData other than to read about it and review some examples, but I would say this:
It sounds like your data is simply coming out of CoreData unsorted, and the order is in fact not guaranteed UNLESS you provide some additional hint about how you would like it sorted, with say a sort descriptor or something.
Sorry I can't provide a concrete reference, but there has to be a way to both fetch data and specify the order in which it is returned.
Alternatively, you could (behind the scenes) fetch all the table data from CoreData and then sort it yourself, but I think that defeats the purpose of using CoreData in the first place and discards a lot of the functionality of CoreData that is likely more efficient than anything you could write yourself to massage the data.
I am trying to create a Core Data iPhone application. One of the entities I'm tracking is cars, and one attribute of each car is "manufacturer".
In the "edit car" section of my application, I have a UIPickerView that needs to be loaded with each of the unique manufacturers that have previously been entered into the system. What I'm trying to do is create an NSFetchRequest to get an array of unique "manufacturer" attributes and use that to populate the UIPickerView.
The problem I'm running into is that whether there are zero records or 100 in the data store, there is always one record in the executed fetch request at element zero with a value #"".
Am I doing this wrong or is there an easier way to do this? I wish I could just run a quick sql query!!!
My code is below:
// Populate the manufacturerNameList array
NSManagedObjectContext *moc = [self.selectedLease managedObjectContext];
NSEntityDescription *ed = [NSEntityDescription entityForName:#"Car" inManagedObjectContext:moc];
NSFetchRequest *fetchRequest = [[[NSFetchRequest alloc] init] autorelease];
[fetchRequest setEntity:ed];
// Get only manufacturer and only uniques
[fetchRequest setResultType:NSDictionaryResultType];
[fetchRequest setPropertiesToFetch:[NSArray arrayWithObjects:#"manufacturer",nil]];
[fetchRequest setReturnsDistinctResults:YES];
// Sort by manufacturer in ascending order
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"manufacturer" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
NSError *error = nil;
self.manufacturerNameList = [moc executeFetchRequest:fetchRequest error:&error];
if (error) {
// Handle the error
}
NSLog(#"The count of self.propertyNameList is %i",[self.propertyNameList count]);
Thanks!
manufacturerNameList is going to be an array of Car entities, not manufacturer names. Also, you need to pass an NSArray of NSPropertyDescription objects to setPropertiesToFetch not just attribute names.
Here is how you set the property:
NSDictionary *entityProperties = [ed propertiesByName];
[fetchRequest setPropertiesToFetch:[NSArray arrayWithObjects:[entityProperties objectForKey:#"manufacturer"], nil]];
The results from executeFetchRequest: will be an NSArray of Car entities, so you'll then have to extract the manufacturer attribute values in a loop or something.
You may want to consider creating a Manufacturer entity that your Car entity references, that will allow you to query more in the way you are attempting to right now.
Another approach would be to create an entity for manufacturers and have a relationship between Car and Manufacturer such that a Car has one Manufacturer and a Manufacturer has many Cars:
Car <<--> Manufacturer
The Manufacturer entity could have a string attribute its "name".
Then, you could get the full list of manufacturer names by fetching all the Manufacturer objects and looking at the "name" property.
The simplest explanation is that you have a car entity that has an empty manufacturer value. When the predicate sorts the fetch, the blank string will be ranked first.
I would log the entire self.propertyNameList and see what you're actually getting back.
The Core Data Documentation states that:
The fetch request associated with the [fetched] property can have a sort ordering, and thus the fetched property may be ordered.
How do I specify the sort descriptors for the fetched property in Xcode's data model editor? I can't find a relevant field anywhere. I'm developing for the iPhone platform, if this makes any difference.
If this is not possible via the graphical model editor, how do I go about modifying the fetch request for the fetched property in code so that it has a sort descriptor?
You can actually grab the model fetched property and add the sort descriptors to it (again, in code). I did this in the standard method that XCode generates in your AppDelegate if you choose one of the templates with Core Data:
By the way. This sorts ALL fetched properties on ALL models in your data model. You could get fancy and adaptive with it, but it was the most succinct way to handle sorting the 7 separate models that each had fetched properties that needed to be sorted by name. Works well.
/**
Returns the managed object model for the application.
If the model doesn't already exist, it is created by merging all of the models found in the application bundle.
*/
- (NSManagedObjectModel *)managedObjectModel {
if (managedObjectModel != nil) {
return managedObjectModel;
}
managedObjectModel = [[NSManagedObjectModel mergedModelFromBundles:nil] retain];
// Find the fetched properties, and make them sorted...
for (NSEntityDescription *entity in [managedObjectModel entities]) {
for (NSPropertyDescription *property in [entity properties]) {
if ([property isKindOfClass:[NSFetchedPropertyDescription class]]) {
NSFetchedPropertyDescription *fetchedProperty = (NSFetchedPropertyDescription *)property;
NSFetchRequest *fetchRequest = [fetchedProperty fetchRequest];
// Only sort by name if the destination entity actually has a "name" field
if ([[[[fetchRequest entity] propertiesByName] allKeys] containsObject:#"name"]) {
NSSortDescriptor *sortByName = [[NSSortDescriptor alloc] initWithKey:#"name" ascending:YES];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sortByName]];
[sortByName release];
}
}
}
}
return managedObjectModel;
}
You don't specify them in the graphical editor (as far as I know).
You specify them in the code where you make the fetch.
NSFetchRequest* request = [[NSFetchRequest alloc] init];
NSEntityDescription* entity = [NSEntityDescription entityForName:#"whatYouAreLookingFor"
inManagedObjectContext:self.managedObjectContext];
[request setEntity:entity];
// here's where you specify the sort
NSSortDescriptor* sortDescriptor = [[NSSortDescriptor alloc]
initWithKey:#"name" ascending:YES];
NSArray* sortDescriptors = [[[NSArray alloc] initWithObjects: sortDescriptor, nil] autorelease];
[request setSortDescriptors:sortDescriptors];
[sortDescriptor release];
fetchedResultsController = [[NSFetchedResultsController alloc]
initWithFetchRequest:request
managedObjectContext:self.managedObjectContext
sectionNameKeyPath:nil
cacheName:#"myCache"];
The modeling tool doesn't appear to have a way to set the sort descriptors on the fetch request.
It should be possible[1] to, after loading the model but before associating it with a persistent store coordinator, to find the fetched property descriptions for which you want to control the sort order, and replace their fetch requests with fetch requests that have sort descriptors set on them.
[1] In principle this should work. In practice, I have not done so or tested it.
Using Tim Shadel's great answer I added per-NSManagedObject subclass sorting...
...in Tier.m (which is a NSManagedObject subclass)...
+ (void)initialize
{
if(self == [Tier class])
{
NSFetchedPropertyDescription *displayLessonPropertyDescription = [[[Tier entityDescription] propertiesByName] objectForKey:#"displayLesson"];
NSFetchRequest *fetchRequest = [displayLessonPropertyDescription fetchRequest];
NSSortDescriptor *sortByName = [[NSSortDescriptor alloc] initWithKey:#"displayOrder" ascending:YES];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sortByName]];
[sortByName release];
}
}
For a single fetched property, Swift 4, Xcode 9.4:
// retrieve the fetched property's fetch request
let fetchedPropertyRequest = (modelName.entitiesByName["entityName"]!.propertiesByName["fetchedPropertyName"] as! NSFetchedPropertyDescription).fetchRequest
// set up the sort descriptors
let sortDescriptors = [NSSortDescriptor(key: "keyName", ascending: true)]
// add the sort descriptors to the fetch request
fetchedPropertyRequest!.sortDescriptors = sortDescriptors
Here's the same thing the loooonnnnnnggggggg way:
// retrieve the fetched property's fetch request
let theEntityDescription: NSEntityDescription = modelName.entitiesByName["entityName"]!
let theFetchedPropertyDescription = theEntityDescription.propertiesByName["fetchedPropertyName"]! as! NSFetchedPropertyDescription
let theFetchedPropertyRequest = theFetchedPropertyDescription.fetchRequest
// set up the sort descriptors
let sortDescriptor1 = NSSortDescriptor(key: "keyName", ascending: true)
let theSortDescriptors = [sortDescriptor1]
// add the sort descriptors to the fetch request
theFetchedPropertyRequest!.sortDescriptors = theSortDescriptors
Note: for this example, I force-unwrapped values. Make sure that you account for optional values in your actual code!
Sadly, though, the ability to sort is somewhat limited. For example, you cannot take a field that is an NSString containing a number, and sort it numerically, at least not with a SQLite backing store. As long as you are sorting alphabetically on strings, numerically only on values stored as numbers and so forth, though, the NSSortDescriptor applied to the fetch request works just fine.
Put this into your NSManagedObject subclass:
+ (void)initialize
{
if (self != [EntityManagedObjectSubClass class]) return;
NSManagedObjectModel *managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil];
NSEntityDescription *entityDescription = [managedObjectModel entitiesByName][#"entityName"];
NSFetchedPropertyDescription *fetchedPropertyDescription = [entityDescription propertiesByName][#"fetchedPropertyName"];
NSFetchRequest *fetchRequest = [fetchedPropertyDescription fetchRequest];
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:#"sortDescriptorKey" ascending:YES];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];
}
Replace EntityManagedObjectSubClass, entityName, fetchedPropertyName and sortDescriptorKey with your own stuff.
Jeff, if the strings are right-aligned, you could just sort on the strings; " 123" > " 23" and so on. But iirc ascii space is after the numbers, and if so, then what you would do is create a dynamic property that is an NSNumber (which supports the compare: method), and use the numberFromString: method to make a number from the string. Then you can specify the number field in the sort. In the interface:
#property NSString *stringIsaNumber; // in the data model
#property NSNumber *number;
in the implementation:
#dynamic stringIsaNumber;
- (NSNumber *) number ;
{ return [self.stringIsaNumber numberFromString]; }
- (void) setNumber:(NSNumber *)value;
{ self.stringIsaNumber = [NSString stringWithFormat:#"%5i",value) }
ps plz forgive coding errors, this is off the top of my head.