I have a CoreData (SQLite) datamodel in xcode like so:
Friends Table
email
name
username
belongsToGroups
Groups Table
title
peopleInGroup
So the belongsToGroups and peopleInGroups is a many-to-many relationship with each other, both represented by NSSet in the code.
What do I use to query the NSSet for people in my groups and vice versa? (I'm new to CoreData)
With coredata, you can do it simple. Assume we have one object on Groups Table ( group), you want to get all friends belong to group, you can do:
[group. peopleInGroup allObjects]
For more detail:
Get group via title
NSError* error = nil;
NSFetchRequest* fetchRequest = [[NSFetchRequest alloc] init];
NSPredicate *predicate;
NSEntityDescription *entity;
NSArray *fetchedObjects;
Group* group;
entity = [NSEntityDescription
entityForName:[NSString stringWithFormat:#"%#",[Group class]]
inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
predicate = [NSPredicate predicateWithFormat:[NSString stringWithFormat:#"(title like[c] \"%#\")" ,title]];
[fetchRequest setPredicate:predicate];
fetchedObjects = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
if (fetchedObjects.count > 0) {
group = [fetchedObjects lastObject];
}
return group;
}
Get all friend of group
NSMutableArray* friends = [NSMutableArray alloc] init];
[friends addObjectsFromArray:[group. peopleInGroup allObjects]];
Related
I have 2 tables: Users and Comments like so:
Users
user_id (PK)
name
Comments
comment_id (PK)
user_id
comment
I want to get a list of all users and their comments.
How is this done using NSPredicate?
Thanks.
As far as I understood your question, you are using core-data.
First of all, you have to make a small change in your managed object model.
Entity
Users
Attributes
user_id
name
Entity
Comments
Attributes
comment_id
comment
Relationships
Relationship - - - Desination - - - Inverse
user - - - Users - - - NO Inverse
Now , whenever you enter the data for Comments object, associate a user relationship with it as
comment.user=theUser
where theUser is a 'Users' object which you can get from 'Users' table by comparing user_id, for that you can use a simple method as by calling the following method for the userID that you got from comment data
theUser= [self isUserAlreadyExistsWithUserID:userID];
where the method definition could be like in Users NSManagedObject subclass
+(NSManagedObject*)isUserAlreadyExistsWithUserID uniqueValue: (id)uniqueValue
{
NSManagedObjectContext* context=[self managedObjectContext];
NSError*error=nil;
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Users" inManagedObjectContext:context];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"user_id = %#",uniqueValue];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
fetchRequest.entity = entity;
[fetchRequest setPredicate:predicate];
NSArray *objects = [context executeFetchRequest:fetchRequest error:&error];
if(objects && objects.count>0)
{
return [objects objectAtIndex:0];
}
else
{
return nil;
}
}
Now, to fetch comments for particular user in comments NSManagedObject subClass:
+(NSFetchedResultsController*)getCommentsForUser:(Users*)user
{
NSString* cacheName=#"Root";
[NSFetchedResultsController deleteCacheWithName:cacheName];
NSManagedObjectContext* context=[self managedObjectContext];
NSEntityDescription *entity = [NSEntityDescription entityForName:NSStringFromClass([self class]) inManagedObjectContext:context];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:entity];
NSPredicate* predicate=[NSPredicate predicateWithFormat:#"user=%#",user];
fetchRequest setPredicate:predicate];
NSFetchedResultsController *theFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:context sectionNameKeyPath:nil
cacheName:cacheName];
return theFetchedResultsController;
}
Hope this helps.
I think, you need this query:
SELECT Users.*,Comments.comment_id,Comments.comment FROM Users LEFT JOIN Comments ON Users.user_id = Comments.user_id;
This will return list of all users along with their comments. You can modify it, as per your specific requirements.
Are you using CoreData? if yes then use try the following code:
NSEntityDescription *entityDescription = [NSEntityDescription entityForName:#"Users" inManagedObjectContext:self.managedObjectContext];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entityDescription];
[request setRelationshipKeyPathsForPrefetching:[NSArray arrayWithObjects:#"Comments",nil]];
[request setIncludesSubentities:YES];
NSArray* returnArray = [self.managedObjectContext executeFetchRequest:request error:&error];
if([returnArray count] > 0)
{
Users* user = [returnArray objectAtIndex:0];
NSLog(#"%# %# %#", user.user_id, user.name, user.userComments.comment);
}
Also, CoreData uses relationships instead of foreignKeys. Therefore, to get this working you need to setup an inverse relationship userComments (many to one) from Comments to Users.
It is better not to use NSPredicate when making a query. You can simply write a JOIN query. As Apple's documentation also states that the NSPredicate class is used to define logical conditions used to constrain a search either for a fetch or for in-memory filtering. Also it will be easier to use Key-Value Coding. Here is a good explaination to how it can be used. Lets assume you have NSSet of Comments. You can do something like :
[Comments valueForKeyPath:#"users.user_id"];
But, if you really want to use NSPredicate following is the possible way:
NSFetchRequest *fetchReq = [[NSFetchRequest alloc] initWithEntityName:#"Users"];
NSError *error;
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"(user_id == %#)",Comments.user_id];
[fetchReq setPredicate:predicate];
NSArray *result = [self.managedObjectContext executeFetchRequest:fetchReq error:&error];
I am a new bid in iOS development. I am using NSManagedObject of Core Data to perform Insert and Fetch operations. It works perfectly fine. But the problem is, I want to fetch only some selected records (where condition in MySQL) from the table.
For e.g. "select name from users where city='Pune'";
I found NSPredicate to fetch filtered data. But it gives all the data in array and not just the selected one. For e.g. if result for above query is:
Anu
Then the NSPredicate result will give:
fname = Anu
lname = Padhye
city = Pune
id = 3
Is there a way to only fetch selected record/s in iOS Objective-c? Following is the code snippet I am using for NSManagedObject:
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:#"User"];
valueData = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
NSEntityDescription *productEntity=[NSEntityDescription entityForName:#"User" inManagedObjectContext:managedObjectContext];
NSFetchRequest *fetch=[[NSFetchRequest alloc] init];
[fetch setEntity:productEntity];
NSPredicate *p=[NSPredicate predicateWithFormat:#"id == %d", 3];
[fetch setPredicate:p];
//... add sorts if you want them
NSError *fetchError;
NSArray *fetchedProducts=[valueData filteredArrayUsingPredicate:p];
Try this:
NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:#"User"];
request.predicate = [NSPredicate predicateWithFormat:#"city == %# && id == %d", #"Pune", 3];
request.sortDescriptors = #[[NSSortDescriptor sortDescriptorWithKey:#"id" ascending:YES]];
NSArray *results = [managedObjectContext executeFetchRequest:request error:nil];
Results array should now contain all records who have Pune as their city with the id of 3.
I was scratching my head all the way through to get this problem solved my self but unfortunately i couldn't.
So my problem is i have multiple values corresponding to one lectures so i made lectureTpPbl,lectureToProfessor,lecturetoStudyProgram relation of type one to many relationship as shown in image.
i saved into the DB like below:
-(void)saveToDatabase:(NSMutableDictionary *)inData{
LectureDetails *lectureDetail = (LectureDetails *)[NSEntityDescription insertNewObjectForEntityForName:#"LectureDetails" inManagedObjectContext:context];
[lectureDetail setAverageRating:[inData valueForKey:kLectureAverageRating]];
[lectureDetail setCategoryID:[inData valueForKey:kLectureCategoryID]];
[lectureDetail setCategoryName:[inData valueForKey:kLectureCategoryName]];
[lectureDetail setLectureID:[inData valueForKey:kLectureID]];
[lectureDetail setSemesterID:[inData valueForKey:#"SemesterID"]];
[lectureDetail setStartTime:[inData valueForKey:kLectureStartTime]];
[lectureDetail setRatingType:[inData valueForKey:kRatingType]];
[lectureDetail setMonth:[NSNumber numberWithInt:[[[[inData valueForKey:kLectureDate] componentsSeparatedByString:#"-"] objectAtIndex:1] integerValue]]];
[lectureDetail setDateOnly:[NSNumber numberWithInt:[[[[inData valueForKey:kLectureDate] componentsSeparatedByString:#"-"] objectAtIndex:2] integerValue]]];
for (id prof in [inData valueForKey:#"Professors"]) {
ProfessorsInLecture *profData = (ProfessorsInLecture *)[NSEntityDescription insertNewObjectForEntityForName:#"ProfessorsInLecture" inManagedObjectContext:context];
profData.professorID=[NSNumber numberWithInt:[[prof valueForKey:#"ProfessorID"]integerValue]] ;
profData.professorFirstName=[prof valueForKey:#"ProfessorFirstName"];
profData.professorLastName=[prof valueForKey:#"ProfessorLastName"];
profData.ProfessorUserName=[prof valueForKey:#"ProfessorUserName"];
[lectureDetail addLectureToProfessorObject:profData];
}
for (id prog in [inData valueForKey:#"StudyPrograms"]) {
StudyProgramInLecture *stdyProgramData = (StudyProgramInLecture *)[NSEntityDescription insertNewObjectForEntityForName:#"StudyProgramInLecture" inManagedObjectContext:context];
stdyProgramData.sMID=[prog valueForKey:#"SMID"];
[lectureDetail addLectureToStudyProgramObject:stdyProgramData];
}
for (id pblData in [inData valueForKey:#"PBLs"]) {
PBLinLectures *pbl = (PBLinLectures *)[NSEntityDescription insertNewObjectForEntityForName:#"PBLinLectures" inManagedObjectContext:context];
[pbl setLecturePBLID:[pblData valueForKey:#"LecturePBLID"]];
[pbl setPBLID:[pblData valueForKey:#"PBLID"]];
[lectureDetail addLectureToPBLObject:pbl];
}
NSError *error1;
if (![context save:&error1])
{
//NSLog(#"ERROR--%#",error);
abort();
}
}
all the data is getting save correctly but i am getting problem in fetching the data.
Now suppose i have to fetch a lecture whose semesterID=7 and month=12 and day=20 and (in relation table)sMID=2 and (in relation table)pBLID=4.
what i have done so far is to fetch is
-(NSMutableArray *)fetchDataforMonth:(NSNumber *)month andDate:(NSNumber *)dateOnly
{
NSEntityDescription *entity = [NSEntityDescription entityForName:#"LectureDetails" inManagedObjectContext:context];
// Setup the fetch request
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entity];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"ANY lectureToPBL.pBLID ==%#", [NSNumber numberWithInt:[[[UserDetail sharedInstance].userDetail valueForKey:#"pBLID"]integerValue]]];
NSPredicate *pred1 =
[NSPredicate predicateWithFormat:#"(dateOnly == %#)",dateOnly];
NSPredicate *pred2 =
[NSPredicate predicateWithFormat:#"(month == %#)",month];
NSPredicate *pred3 =
[NSPredicate predicateWithFormat:#"(semesterID == %#)",[NSNumber numberWithInt:[[[UserDetail sharedInstance].userDetail valueForKey:#"semesterID"]integerValue]]];
NSPredicate *pred4 = [NSPredicate predicateWithFormat:#"ANY lectureToStudyProgram.sMID ==%#", [NSNumber numberWithInt:[[[UserDetail sharedInstance].userDetail valueForKey:#"programID"]integerValue]]];
NSArray *compPredicatesList = [NSArray arrayWithObjects:pred1,pred2,pred3,predicate,pred4, nil];
NSPredicate *CompPrediWithAnd = [NSCompoundPredicate andPredicateWithSubpredicates:compPredicatesList];
[request setPredicate: CompPrediWithAnd];
// Fetch the records and handle an error
NSError *error;
NSMutableArray *mutableFetchResults = [[context executeFetchRequest:request error:&error] mutableCopy];
return mutableFetchResults;
}
If there is one sMID and one pBLID then fetching is working fine otherwise i am not getting an object in fetch result.
Suppose i have a lecture whose semesterID is 7 and month=12 and day=20 and have multiples sMID such as 1,2,3 and multiples pBLID such as =4,5,6
and i want to fetch a lecture whose month=12 and day=20 and sMID=2 and pBLID=4
Can anybody tell me how to do that?
Any Help will be appreciated.
Thanks
First filter the Lecturers whose month=12 and day=20 from LectureDetails entity:
NSPredicate *pred = [NSPredicate predicateWithFormat:#"(month == %#) AND (dateOnly == %#) ",month, dateOnly];
[request setPredicate: pred];
NSError *error;
NSArray *lectureList = [context executeFetchRequest:request error:&error];
then filter this array with pBLID and sMID.
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"(ANY lectureToStudyProgram.sMID ==%#) AND (ANY lectureToStudyPBL.pBLID ==%#)", sMID, pBLID];
lectureList = [lectureList filteredArrayUsingPredicate:predicate];
Now lectureList will give you the result.
my program has a sqlite database with two related tables. One called "Rank" and other one called "Requirement"
I want to fetch all rows from the "Requirement" table that has a relationship with the specific row in a "Rank" table. Following is my code, it grabs the whole table, but I get the specified rows only according to the above mentioned rule.
-(NSArray *) getAllRequirementsForTheRank:(Rank *) rank
{
NSError *error;
NSFetchRequest *fetchRequest = [[[NSFetchRequest alloc] init]autorelease];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Requirement" inManagedObjectContext:self.context];
[fetchRequest setEntity:entity];
NSPredicate *searchType = [NSPredicate predicateWithFormat:#"Rank = %#", rank];
[fetchRequest setPredicate:searchType];
NSArray *scoutRequirementArray = [self.context executeFetchRequest:fetchRequest error:&error];
for (Requirement *r in scoutRequirementArray)
{
NSLog(#"Requirementttt : %# :", r.requirementName);
}
return scoutRequirementArray;
}
If you have the relationship modelled in core data, just get the linked objects from the relationship property. You don't need another fetch request. rank.requirements will give you an NSSet of everything you need. (I'm assuming names for your object and properties here).
I have a problem where I am inserting entities A in a context. Right after I insert all of the entities A I execute a fetch request on the context:
NSEntityDescription* entity = [NSEntityDescription entityForName:#"A" inManagedObjectContext:ctx];
NSFetchRequest* fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:entity];
NSError* fetchError;
NSArray* results = [ctx executeFetchRequest:fetchRequest error:&fetchError];
This code above is able to get all of them and I can see them in the NSLog...
Right after on the same context I try to fetch all entities A that have age = 5, like this:
(I assign "age" to the attirbute and a NSString #"5" to the value)
NSEntityDescription* entity = [NSEntityDescription entityForName:#"A" inManagedObjectContext:ctx];
NSFetchRequest* fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:entity];
NSPredicate *filter = [NSPredicate predicateWithFormat:#"%K == %#",attr,value];
[fetchRequest setPredicate:filter];
NSError* fetchError;
NSArray* results = [ctx executeFetchRequest:fetchRequest error:&fetchError];
THE PROBLEM IS that even though the NSLog shows an entity A with age 5 this last fetch request returns always null! Nothing.
Any suggestions? Why fetching all of them shows entities with age 5 and filtering for age 5 only does not work right after on the same context?
Thanks
Try setting age to an instance of NSNumber initalized to 5 rather than the NSString #"5".