核心数据：从多个实体或关系获取结果 [英] Core Data: Fetch result from multiple entities or relationship

问题描述

我有两个实体。 员工实体

  @interface员工：NSManagedObject 
 
 @property（nonatomic，retain）NSString * dept; 
 @property（nonatomic，retain）NSString * email; 
 @property（nonatomic，retain）NSString * name; 
 @property（nonatomic，retain）Department * deptEmp; 
 
 @end 
  

和部门实体

  @interface部门：NSManagedObject 
 
 @property（nonatomic，retain）NSString * 位置; 
 @property（nonatomic，retain）NSString * name; 
 @property（nonatomic，retain）Employee * deptEmp1; 
  

我试图从以下谓词中获取信息：

  NSMutableString * queryString = [NSMutableString stringWithFormat：@（name ='Apple'）AND（deptEmp1.location like'Cupertino'）]; 
 
 NSEntityDescription * entityDescription = [NSEntityDescription entityForName：@EmployeeinManagedObjectContext：self.managedObjectContext]; 
  

提取请求

  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]; 
} 
  

但这里我从来没有结果。

<我不知道你想要实现什么，但如果你想检索一个 Employee 谁工作具体部门名称和在特定位置，我将使用以下代码：

  NSMutableString * queryString = [NSMutableString stringWithFormat ：@deptEmp1.name ==％@ AND deptEmp1.location ==％@，@Apple，@Cupertino]; 
 NSEntityDescription * entityDescription = [NSEntityDescription entityForName：@EmployeeinManagedObjectContext：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）; 
} 
  

少量注释

为什么对请求使用锁定？
你设置了一个inverse rel？
也许你需要在部门和员工之间建立一对多的关系？ / p>

尝试让我知道。

编辑 b

尝试这个。我没有注意到你的问题中的查询字符串。

  NSPredicate * predicate = [NSPredicate predicateWithFormat：@deptEmp1.name = =％@ AND deptEmp1.location ==％@，@Apple，@Cupertino]; 
 NSEntityDescription * entityDescription = [NSEntityDescription entityForName：@EmployeeinManagedObjectContext：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）; 
} 
  

编辑2 b

  NSEntityDescription * entityDescription = [NSEntityDescription entityForName：@EmployeeinManagedObjectContext：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）; 
} 
  

I have two entities. Employee entity

@interface Employee : NSManagedObject

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

@end

and Department entity

@interface Department : NSManagedObject

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

I am trying to fetch information from both with following predicate

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

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

And Fetch Request is

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

Setting Predicate

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

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

Fetching Result

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

But here I never get result.

解决方案

I'm not sure what you want to achieve but if you want to retrieve an Employee who works in a specific department name and in a specific location, I'll use a the following code:

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);
}

Few notes

Why do you use a lock on the request? Have you set a inverse rel? Maybe do you need to set up a one-to-many rel between Department and Employee?

Try and let me know.

Edit

Try this one. I didn't notice the query string in your question.

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);
}

Edit 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);
}

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