CODEWITHSUNDEEP
ioscore-data
SubmarineX
SubmarineX

Reputation: 850

Core Data: fetch result from two entities, and the result contain info in two entities

There are two entities:

enter image description here

I want to make a course table.

The first entity is Course, the second is TimeAndPlace. At university, there are some courses and one course maybe has different time or place. Now I want to fetch Courses and their associated TimeAndPlaces in every weekday. But there some limits: if current week is between start week and last week whose period in term, the course is needed; in this courses, select the course whose weekday equal to a certain weekday. Finally, I want to get the course and their associated time and place.

I'm not too familiar with Core Data, Can you help me?

Edited: Just like SQL:

SELECT Course.courseName, TimeAndPlace.courseLocation, TimeAndPlace.courseOrder
FROM Course, TimeAndPlace
WHERE Course.startWeekTheCourseInTheTerm <= currentWeek AND Course.lastWeekTheCourseInTheTerm >= currentWeek AND timeAndPlaces.weekday == currentweekday;

effect drawing:

enter image description here

Upvotes: 2

Views: 414

Answers (1)

geo
geo

Reputation: 1791

maybe something like this? with an 1:n relation it's not that complicated, will get more fun with n:m :P

NSFetchRequest* fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:[NSEntityDescription entityForName:@"Course" inManagedObjectContext:context]];

NSPredicate* = [NSPredicate predicateWithFormat:@"startWeekTheCourseInTheTerm <= %d AND lastWeekTheCourseInTheTerm >= %d AND timeAndPlaces.weekday == %d", currentWeek, currentWeek, weekday];
[fetchRequest setPredicate:predicate];

or if you need complete week (for example to show in a tableView)

NSPredicate* = [NSPredicate predicateWithFormat:@"startWeekTheCourseInTheTerm <= %d AND lastWeekTheCourseInTheTerm >= %d", currentWeek, currentWeek];
[fetchRequest setPredicate:predicate];

[fetchRequest setSortDescriptors:[NSArray arrayWithObject:[[NSSortDescriptor alloc] initWithKey:@"timeAndPlaces.weekday" ascending:YES]]];

sort by weekday and courseOrder:
(so you have

-> Monday
--> 1
--> 2
--> 3
-> Tuesday
--> 1
...

[fetchRequest setSortDescriptors:[NSArray arrayWithObjects:[[NSSortDescriptor alloc] initWithKey:@"timeAndPlaces.weekday" ascending:YES], [[NSSortDescriptor alloc] initWithKey:@"timeAndPlaces.courseOrder" ascending:YES], nil]];

last step: fetching

NSError* err = nil;
list = [NSMutableArray arrayWithArray:[context executeFetchRequest:fetchRequest error:&err]];
[fetchRequest release];

Upvotes: 1

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