使用NSPredicate與核心數據建立深層關係

Question

我有一個NSArrayController，companiesController綁定到頂級核心數據實體Companies。

甲Company有許多Department「s和一個Department有許多Employee;這些由一對多關係departments和employees表示。

基於一個Employee我以爲我可以動態地用於過濾基於薪金UI所謂的方法中做到這一點的屬性salary：

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY departments.employees.salary < %@", [NSNumber numberWithInt:23000]]; 
[companiesController setFilterPredicate:predicate]; 

唉，這給我的錯誤：-[NSCFSet compare:]: unrecognized selector sent to instance。

Answer 1

在這種情況下不允許使用多對多密鑰。

相反，你可以做到以下幾點：

1. 通過添加一個「過濾器」標記（布爾）屬性Department實體修改數據模型。
2. 創建一個方法：獲取所有Department對象，將滿足條件的後半部分的部門的過濾器標誌設置爲YES，將其他部門的過濾器標誌設置爲NO，然後保存。
3. 使用公司謂詞中的過濾器標誌。

代碼更改（步驟3）：

//NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY departments.employees.salary < %@", [NSNumber numberWithInt:23000]]; 
    [self setDeptFilter:23000]; 
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY depts.filter == YES"]; 
    [companiesController setFilterPredicate:predicate]; 

而新的方法（步驟2）：

- (void)setDeptFilter:(NSUInteger)salary { 
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; 

    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Department" inManagedObjectContext:self.managedObjectContext]; 
    [fetchRequest setEntity:entity]; 

    NSError *error = nil; 

    // fetch all Department objects 
    NSArray *array = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error]; 

    [fetchRequest release]; 

    if (error) { 
     NSLog(@"Error fetching Departments %@, %@", error, [error userInfo]); 
     abort(); 
    } 

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY emps.salary < %@",[NSNumber numberWithInteger:salary]]; 
    NSArray *filterArray = [array filteredArrayUsingPredicate:predicate]; 

    // set filter flag to YES for the departments that meet the criteria 
    for (Department *dep in filterArray) { 
     dep.filter = [NSNumber numberWithBool:YES]; 
    } 

    NSMutableArray *diffArray = [array mutableCopy]; 
    [diffArray removeObjectsInArray:filterArray]; 

    // set filter flag to NO for the departments that do NOT meet the criteria 
    for (Department *dep in diffArray) { 
     dep.filter = [NSNumber numberWithBool:NO]; 
    } 

    [diffArray release]; 

    // save 
    if ([self.managedObjectContext hasChanges] && ![self.managedObjectContext save:&error]) { 
     NSLog(@"Unresolved error %@, %@", error, [error userInfo]); 
     abort(); 
    } 
} 

Answer 2

你也可以做到這一點使用子查詢。

獲取所有部門。在「的」關係是公司對多個部門的倒數：

-(void)printDepartmentsWithSalaryHigherThan:(int)salary inContext:(NSManagedObjectContext *)context {  
    NSFetchRequest *request = [[NSFetchRequest alloc ]init]; 
    request.entity = [NSEntityDescription entityForName:@"Department" inManagedObjectContext:context]; 
    request.predicate = [NSPredicate predicateWithFormat:@"SUBQUERY(employees, $emp, $emp.salary > %@).@count > 0", [NSNumber numberWithInt:salary]]; 

    for(Department *dep in [context executeFetchRequest:request error:nil]){ 
     NSLog(@"Department: %@", dep.depName); 
     NSLog(@"in Company: %@", dep.of.compName); 
    } 
    [request release]; 
} 

或者，如果你有更多的公司，只是想有一個員工提供工資的企業一定量「高於」。基於子查詢結果的子查詢

-(void)printCompaniesWithHigherSalaryThan:(int)salary inContext:(NSManagedObjectContext *)context { 
    NSFetchRequest *request = [[NSFetchRequest alloc ]init]; 
    request.entity = [NSEntityDescription entityForName:@"Company" inManagedObjectContext:context]; 
    request.predicate = [NSPredicate predicateWithFormat:@"SUBQUERY(departments, $dep, SUBQUERY($dep.employees,$emp,$emp.salary > %@).@count > 0).@count > 0", [NSNumber numberWithInt:salary]]; 

    for(Company *c in [context executeFetchRequest:request error:nil]){ 
     NSLog(@"Company: %@", c.compName); 
    } 
    [request release]; 
}