I'm implementing search bar in iphone app. I have list of Workers, each have attributes: firstName, lastName, company. Sections of table view are set to company attribute.
I did set predicate when searching:
NSPredicate *predicate =[NSPredicate predicateWithFormat:#"firstName contains[cd] %#", searchBar.text];
and i get error:
NSFetchedResultsController ERROR: The fetched object at index 3 has an out of order section name 'company2. Objects must be sorted by section name'
when I have sortDescriptor:
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"lastName" ascending:YES selector:#selector(caseInsensitiveCompare:)];
I did notice that when I change it to
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"firstName"` ascending:YES selector:#selector(caseInsensitiveCompare:)];
now search works correctly with no error. Does initWithKey param must match attribute name in predicate? I don't get it.
From the NSFetchedResultsController docs:
The fetch request must have at least
one sort descriptor. If the controller
generates sections, the first sort
descriptor in the array is used to
group the objects into sections; its
key must either be the same as
sectionNameKeyPath or the relative
ordering using its key must match that
using sectionNameKeyPath.
In your case, you need to use two sorts (in an array.) Element one should be a sort on the company name attribute and second element should sort on the lastName/firstName attribute.
Related
I am using UIManagedDocument with Parent Child context.
In my child context I do the following
Code 1
NSSet *results = [self.event.memberships filteredSetUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) {
return ([[evaluatedObject deleted] boolValue] == NO);
}]];
Above code returns the expected results (only Not deleted members for the event).
Code 2
But this code does not. It fetches all records.
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"deleted == NO"];
NSSet *results = [self.event.memberships filteredSetUsingPredicate:predicate];
It seems confusing. Both should return same results, but predicateWithBlock returns correct results where as predicateWithFormat returns all records.
What are the pros and cons of using predicateWithBlock instead of predicateWithFormat?
The problem is that you have defined an attribute deleted for your entity. That conflicts with the isDeleted method of NSManagedObject, so you should rename that attribute.
The following "experiment" shows that strange things happen if you call your attribute "deleted" (c is a managed object with a custom deleted attribute):
// Set custom "deleted" property to YES:
c.deleted = #YES;
// Use the property, as your Code 1
NSLog(#"%#", [c deleted]);
// Output: 1
// Use Key-Value Coding, as your Code 2
NSLog(#"%#", [c valueForKey:#"deleted"]);
// Output: 0
// Now really delete the object and try again:
[context deleteObject:c];
NSLog(#"%#", [c valueForKey:#"deleted"]);
// Output: 1
Your "Code 1" refers to the property, therefore it returns the expected result. "Code 2" uses Key-Value Coding, and [c valueForKey:#"deleted"] returns YES if the object
actually has been deleted from the context!
So renaming that attribute should solve your problem. Unfortunately the compiler does not
emit warnings if an attribute name conflicts with a built-in method.
Use the formatting placeholder to replace the bool value:
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"%K == %#",
#"deleted", #(NO)];
Your use of the key path is probably ok, but the right-hand side probably doesn't look like "NO" to the parser.
My Core Data model has a Note entity with a to-many relationship to a Link entity, accessed through a links property on Note.
I'm trying to fetch the count of the links property for each note in Core Data. To do so, I followed the example at the link below, but I'm getting an unexpected result.
Chained expressions to perform calculations in Core Data
Here's how I'm configuring the fetch request and related expression descriptions:
// Create the expression description that should return the link count for each note.
NSExpression *linksExpression = [NSExpression expressionForKeyPath:#"links"];
NSExpression *countExpression = [NSExpression expressionForFunction:#"count:" arguments:#[linksExpression]];
NSExpressionDescription *linkCountExpressionDescription = [[NSExpressionDescription alloc] init];
linkCountExpressionDescription.name = #"linkCount";
linkCountExpressionDescription.expression = countExpression;
linkCountExpressionDescription.expressionResultType = NSInteger32AttributeType;
// Execute a fetch request that should return an array of dictionaries, each with a single "linkCount" key.
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:#"Note"];
fetchRequest.resultType = NSDictionaryResultType;
fetchRequest.propertiesToFetch = #[linkCountExpressionDescription];
NSArray *countsArray = [self.managedObjectContext executeFetchRequest:fetchRequest error:nil];
The SQLite store I'm working with contains 1000 notes, so I expect to get an array of 1000 dictionaries, each containing a LinkCount key and the count of its links relationship. Instead, I get a single dictionary that gives me the total count of all links.
What should I do differently to get the link counts for each note?
I think I'm just missing something obvious here, but it's one of those frustrating things that's somehow eluding me.
I have a Core Data Entity called ProjectEntry. The ProjectEntry objects are displayed in uitableviews, using various attributes, arranged by date (attributes include things like "dateAsNSDate"[NSDate], "month"[NSString], "year"[NSString], "dayOfWeek"[NSString]).
I'm using an NSFetchedResultsController to populate the table views.
When I initially create and save the ProjectEntry object, the "dateAsNSDate" attribute is parsed and converted into various NSStrings. One string, also an attribute, is called "concatMonthAndYear". It takes the "month" and "year" strings and just joins them. So I get things such as "January 2014", "February 2015", etc.
I use the "concatMonthAndYear" as my cell.textLabel.text string to display in my tableview cells.
I use the NSDate attribute to sort the tableview rows (sortDescriptor), and the "year" attribute as my section headers (sectionNameKeyPath).
So right now, I'd have a tableview section called "2014", with tableview rows each representing a Core Data object, named things like "January 2014", February 2014", etc, in said section.
I can tap on one of those rows, segue to another tableview, and list all objects created in January 2014, for example, by using an NSPredicate on the second tableview.
However, on my first tableview, each Core Data object created is represented by its own tableview row. So I'll get multiple rows reading "January 2014" or "May 2015" or whatever. They're valid saved objects, and I want them, but I'd like to prevent a new row from being created if that "concatMonthAndYear" already exists. If a row titled "January 2014" already exists, I don't want a new row created. I want the new Core Data object stored, just not a new tableviewrow representing it. I only need one row with "January 2014", for example, to segue into a table listing ALL the entities from January 2014.
I know how to use an NSPredicate to get ALL the January 2014 objects into the second table, but how do I get JUST ONE object into the first table?
Is NSPredicate not the right device for that? Should I be somehow preventing a new cell from being created in the UITableView delegate methods? Each tableview row should be unique, and I'm stuck on whether it should be handled with the NSFetchedResults controller or in the tableview delegate methods?
Or some other way?
Can someone point in the right direction?
EDITED TO INCLUDE CODE:
- (void)setupFetchedResultsController
{
// 1 - Decide which Entity
NSString *entityName = #"ProjectEntry";
NSLog(#"Setting up a Fetched Results Controller for the Entity named %#", entityName);
// 2 - Request Entity
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:entityName];
[request setReturnsDistinctResults:YES];
[request setResultType:NSDictionaryResultType];
[request setPropertiesToFetch:#[#"monthYearTableSecHeader", #"year"]];
// 3 - Filter it
//request.predicate = [NSPredicate predicateWithFormat:#" "];
// 4 - Sort it
request.sortDescriptors = [NSArray arrayWithObjects:[NSSortDescriptor sortDescriptorWithKey:#"year"
ascending:NO],
[NSSortDescriptor sortDescriptorWithKey:#"dateAsNSDate"
ascending:YES
selector:#selector(localizedCaseInsensitiveCompare:)], nil];
//5 - Fetch
self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request
managedObjectContext:self.managedObjectContext
sectionNameKeyPath:#"year"
cacheName:nil];
[self performFetch];
}
You could use
[fetchRequest setReturnsDistinctResults:YES];
[fetchRequest setResultType:NSDictionaryResultType];
[fetchRequest setPropertiesToFetch:#[#"concatMonthAndYear", #"year"]];
This will cause the fetch request to return distinct dictionary objects corresponding to "January 2014", etc. objects.
However, you cannot use a fetch request controller's delegate methods (to hear of updates to the data).
If you need to hear updates, I suggest you add a layer of indirection to your data, where MonthEntry is an object representing yearly months and have a one to many relationship with ProjectEntry, which is your normal entity. This way, you can set the fetch request entity to MonthEntry.
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];
I am trying to parse a lot of text files and organize their contents as managed objects. There are a lot of duplicates in the text files, so one of the "collateral" tasks is to get rid of them.
What i am trying to do in this respect is to check whether an entity with the given content exists, and if it doesn't, i create one. However, i have different entities with different attributes and relationships. What i want is a kind of function that would take a number of attributes as an input and return a new NSManagedObject instance, and i wouldn't have to worry if it was inserted into the data store or fetched from it.
Is there one?
I must also say that i am a noob at core data.
Some more detail, if you want:
I am trying to write a sort of dictionary. I have words (Word{NSString *word, <<-> Rule rule}), rules (Rule{NSString name, <->>Word word, <<->PartOfSpeech partOfSpeech, <<-> Ending endings}), parts of speech (PartOfSpeech{NSString name, <<-> Rule rule}) (i hope the notation is clear).
Two words are equal, if they have the same word property, and "linked" to the same rule. Two rules are the same, if they have the same endings and part of speech.
So far i've written a method that takes NSPredicate, NSManagedObjectContext and NSEntityDescription as an input, and first queries the datastore and returns an entity if it finds one, or creates a new one, inserts it into the datastore and returns it. However, in this case I cannot populate the new entity with the necessary data (within that method), so i have to either pass an NSDictionary with the names of attributes and their values and insert them, or return by reference a flag as to whether i created a new object or returned an old one, so that i could populate it with the data outside.
But it looks kind of ugly. I'm sure there must be something more elegant than that, i just couldn't find it. Please, help me if you can.
Your basically on the right path. Core Data is an object graph. There not a lot of dynamic built in. There's also no "upsert". like you surmise, you have to fetch and if it doesn't exist, you insert one.
Here is what I have just started using to handle a fetch-or-create scenario. I am using a top level managed object which contains a few to-many relationships to subordinate objects. I have a class that houses a few arrays of data (those are not shown here). This class is responsible for saving and retrieving to and from core data. When the class is created, I do a fetch-or-create to access my top level NSManagedObject.
#implementation MyDataManagerClass
...
#synthesize MyRootDataMO;
- (MyDataManagerClass *) init {
// Init managed object
NSManagedObjectContext *managedObjectContext = [(MyAppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
// Fetch or Create root user data managed object
NSEntityDescription *entityDescription = [NSEntityDescription entityForName:#"MyRootDataMO" inManagedObjectContext:managedObjectContext];
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:entityDescription];
NSError *error = nil;
NSArray *result = [managedObjectContext executeFetchRequest:request error:&error];
if (result == nil) {
NSLog(#"fetch result = nil");
// Handle the error here
} else {
if([result count] > 0) {
NSLog(#"fetch saved MO");
MyRootDataMO = (MyRootDataMO *)[result objectAtIndex:0];
} else {
NSLog(#"create new MO");
MyRootDataMO = (MyRootDataMO *)[NSEntityDescription insertNewObjectForEntityForName:#"MyRootDataMO" inManagedObjectContext:managedObjectContext];
}
}
return self;
}
...