i'm working with 2 entities in coredata :
- worker
- office
A worker work in one (and only one) office.
An office is occupied by several workers.Now I would like populate a TableView with workers, grouped by office. This represent the table view :
Section 1 : Office 1
.........开发者_JAVA技巧.Worker 1 ..........Worker 2 ..........Worker 3 Section 2 : Office 2 (empty) Section 3 : Office 3 ..........Worker 4 ..........Worker 5
In SQL I could use this query :
SELECT *
FROM office
LEFT JOIN worker ON office.officeId = worker.officeId
order by office.name, worker.name
Now working with core data, I'm facing some problems :
- If I fetch office, I can access to workers (from relationship) as a Set, but this is not adapted to work with table view (for sorting and manipulating)
- If I fetch worker and access the office via the relationship, empty offices are not fetched.
How can I fetch data like this with coredata ?
Thanks
I would fetch the offices, then simply sort the workers set (alphabetically, according to a rank attribute, etc) for display in the table. It'll probably make sense to make a method on your Office entity class to returned a sorted array for workers, e.g.:
@implementation Office
- (NSArray *)sortedWorkers
{
return [self.workers sortedArrayUsingDescriptors:
[NSArray arrayWithObjects:
[NSSortDescriptor sortDescriptorWithKey:@"lastName" ascending:YES],
[NSSortDescriptor sortDescriptorWithKey:@"firstName" ascending:YES],
nil]];
}
Fetch your workers and use the offices for the the sections as you have already done. Empty offices should not be shown in a UITableView
as it goes against the HIG.
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