Question

我有两个实体。 Employee实体

@interface Employee : NSManagedObject

@property (nonatomic, retain) NSString * dept;
@property (nonatomic, retain) NSString * email;
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) Department *deptEmp;

@end

和Department实体

@interface Department : NSManagedObject

@property (nonatomic, retain) NSString * location;
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) Employee *deptEmp1;

我正在尝试使用以下谓词

从两者中获取信息

NSMutableString *queryString = [NSMutableString stringWithFormat:@"(name = 'Apple') AND (deptEmp1.location like 'Cupertino')"];

NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Employee" inManagedObjectContext:self.managedObjectContext];

获取请求

NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entityDescription];
[request setResultType:NSDictionaryResultType]; // NSFetchRequestResultType - NSDictionaryResultType
[request setRelationshipKeyPathsForPrefetching:[NSArray arrayWithObjects:@"Department",nil]];
[request setIncludesSubentities:YES];

设置谓词

if(![queryString isEqualToString:@""])
{
        [request setPredicate:[NSPredicate predicateWithFormat:queryString]];
}

NSError *error = nil;
NSArray *returnArray = nil;

获取结果

@synchronized(self)
{
    returnArray = [self.managedObjectContext executeFetchRequest:request error:&error];
}

但在这里我永远不会得到结果。

Answer 1

我不确定您想要实现的目标，但如果您想要检索在特定部门名称和特定位置工作的Employee，我将使用以下代码：

NSMutableString *queryString = [NSMutableString stringWithFormat:@"deptEmp1.name == %@ AND deptEmp1.location == %@", @"Apple", @"Cupertino"]; 
NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Employee" inManagedObjectContext:self.managedObjectContext];

NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entityDescription];
[request setRelationshipKeyPathsForPrefetching:[NSArray arrayWithObjects:@"Department",nil]];
[request setIncludesSubentities:YES];

NSArray* returnArray = [self.managedObjectContext executeFetchRequest:request error:&error];
if([returnArray count] > 0) {

   Employee* emp = [returnArray objectAtIndex:0];
   NSLog(@"%@ %@ %@", emp.name, emp.dept, emp.deptEmp.location);
}

很少有笔记

为什么要对请求使用锁定？你设置了反向rel吗？也许您需要在Department和Employee之间设置一对多的表达式吗？

试着让我知道。

修改

试试这个。我没有注意到你问题中的查询字符串。

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"deptEmp1.name == %@ AND deptEmp1.location == %@", @"Apple", @"Cupertino"]; NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Employee" inManagedObjectContext:self.managedObjectContext]; NSFetchRequest *request = [[NSFetchRequest alloc] init]; [request setEntity:entityDescription]; [request setPredicate:predicate]; [request setRelationshipKeyPathsForPrefetching:[NSArray arrayWithObjects:@"Department",nil]]; [request setIncludesSubentities:YES]; NSArray* returnArray = [self.managedObjectContext executeFetchRequest:request error:&error]; if([returnArray count] > 0) { Employee* emp = [returnArray objectAtIndex:0]; NSLog(@"%@ %@ %@", emp.name, emp.dept, emp.deptEmp.location); }

修改2

NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Employee" inManagedObjectContext:self.managedObjectContext]; NSFetchRequest *request = [[NSFetchRequest alloc] init]; [request setEntity:entityDescription]; [request setRelationshipKeyPathsForPrefetching:[NSArray arrayWithObjects:@"Department",nil]]; NSArray* returnArray = [self.managedObjectContext executeFetchRequest:request error:&error]; for(Employee* emp in returnArray) { NSLog(@"%@", emp); NSLog(@"%@", emp.deptEmp); }

Answer 2

您需要设置反向关系。你的Department对象需要看起来像这样：

@interface Department : NSManagedObject

@property (nonatomic, retain) NSString * location;
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) NSSet *deptEmp1;

就像所有Departement都有一个员工和员工在一个部门的工作。

在您的谓词上，您需要将“deptEmp1.name”调整为“deptEmp.name”

核心数据：从多个实体或关系中获取结果

2 个答案: