Core Data 自动生成及基本数据操作（4）－－关系操作

在ios 中的NSRelationshipDescription中的删除规则一共有四类如下：

//NSNoActionDeleteRule,

无任何删除动作。

如：Ａ表中的关系字段值与Ｂ表中的键值相对应，当删除Ｂ表中的数据时，Ａ中的关系字段值保持不变。

//NSNullifyDeleteRule

空删除规则。

如：Ａ表中的关系字段值与Ｂ表中的键值相对应，当删除Ｂ表中的数据时，Ａ中的关系字段值变为了ＮＵＬＬ。

//NSCascadeDeleteRule,

联动删除规则。

如：当把Ａ表中的关系设置为联动删除时，哪么Ａ表在删除数据时候，将对联动表的数据也进行删除。

//NSDenyDeleteRule

依赖删除规则。

//如删除部门时必须确保该部门员工表中的数据为空或转到别处，否则删除失败。

1对1 单向删除关系。

静态设置。

在Car 表中添加一个关系取名为details,描述关联为CarStyle反向关系名为main,同时将删除规则设置为cascade

在CarStyle表中添加一个关系名为main描述关联为Car反向关系名为details.

 

 

 

动态设置。

NSEntityDescription *entity = [NSEntityDescription entityForName:@"Car" inManagedObjectContext:self.managedObjectContext];
                
                NSDictionary *rlation = [entity relationshipsByName];
                NSRelationshipDescription *relation = [rlation objectForKey:@"details"];对Car表中的details关系进行设置规则
                [relation setDeleteRule:NSCascadeDeleteRule];
                
                [self.managedObjectContext save:nil];

效果：

当删除Car中的数据时 CarStyle相关联的数据也被删除。但在删除CarStyle时不删除Car中的数据，只是将关系字段设置为ＮＵＬＬ。

1对1双向删除关系。

即Ａ表，Ｂ表中的关系字段的删除规则都同时设为NSCascadeDeleteRule

静态设置

将Car和CarStyle的关系字段的删除规则都设置为Cascade

动态设置

NSEntityDescription *entity = [NSEntityDescription entityForName:@"Car"inManagedObjectContext:self.managedObjectContext];
            
                NSDictionary *rlation = [entity relationshipsByName];
                NSRelationshipDescription *relation = [rlation objectForKey:@"details"];
                [relation setDeleteRule:NSCascadeDeleteRule];
            
                entity = [NSEntityDescription entityForName:@"CarStyle" inManagedObjectContext:self.managedObjectContext];
            
                rlation = [entity relationshipsByName];
                relation = [rlation objectForKey:@"main"];
                [relation setDeleteRule:NSCascadeDeleteRule];
                
                [self.managedObjectContext save:nil];

1对Ｎ删除关系。

在一对Ｎ的关系中，需要在ＭＯＤＥＬ文件里设置to - many relationship 打上勾。

如图设置：

当一对多关系想在删除主表记录里，同时删除子表中对应主表数据的所有子表记录。这里需要设置主表的关系字段的删除规则为NSCascadeDeleteRule

动态设置，只能设置删除规则，对于一对多关系不能动态代码控制，只能静态设置好，因为要通过ＭＯＤＥＬ文件生成相应的关系表。

                NSEntityDescription *entity = [NSEntityDescription entityForName:@"Company" inManagedObjectContext:self.managedObjectContext];
                
                NSDictionary *rlation = [entity relationshipsByName];
                NSRelationshipDescription *relation = [rlation objectForKey:@"dept"];
                [relation setDeleteRule:NSCascadeDeleteRule];

1对Ｎ依赖删除关系。

 

静态设置

 

 

插入测试数据。

- (void)insert1V1Data
{
    //在Car表中添加两条数据
    NSManagedObject * car1 = [NSEntityDescription insertNewObjectForEntityForName:@"Car" inManagedObjectContext:self.managedObjectContext];
    
    [car1 setValue:@"1" forKey:@"name"];
    [car1 setValue:@"1" forKey:@"engine"];
    [car1 setValue:@"1" forKey:@"wheel"];
    
    NSManagedObject * car2 = [NSEntityDescription insertNewObjectForEntityForName:@"Car" inManagedObjectContext:self.managedObjectContext];
    
    [car2 setValue:@"2" forKey:@"name"];
    [car2 setValue:@"2" forKey:@"engine"];
    [car2 setValue:@"2" forKey:@"wheel"];
    
    
    NSManagedObject * carstyle1 = [NSEntityDescription insertNewObjectForEntityForName:@"CarStyle" inManagedObjectContext:self.managedObjectContext];
    
    [carstyle1 setValue:@"3" forKey:@"color"];
    [carstyle1 setValue:[NSNumber numberWithInt:3] forKey:@"width"];
    [carstyle1 setValue:[NSNumber numberWithInt:3] forKey:@"height"];
    
    NSManagedObject * carstyle2 = [NSEntityDescription insertNewObjectForEntityForName:@"CarStyle" inManagedObjectContext:self.managedObjectContext];
    
    [carstyle2 setValue:@"4" forKey:@"color"];
    [carstyle2 setValue:[NSNumber numberWithInt:4] forKey:@"width"];
    [carstyle2 setValue:[NSNumber numberWithInt:4] forKey:@"height"];
    
    [car1 setValue:carstyle1 forKey:@"details"];
    [carstyle1 setValue:car1 forKey:@"main"];
    
    [car2 setValue:carstyle2 forKey:@"details"];
    [carstyle2 setValue:car2 forKey:@"main"];
    
    [self.managedObjectContext save:nil];
    
}

- (void)delete1V1Data:(NSInteger)table
{
    if (table==1)
    {
        NSManagedObjectContext *context = [self managedObjectContext];
        NSEntityDescription *entity = [NSEntityDescription entityForName:@"Car" inManagedObjectContext:context];
        NSFetchRequest *cmd = [[[NSFetchRequest alloc]init]autorelease];
        [cmd setEntity:entity];
        //设置查询条件
        NSPredicate *condition = [NSPredicate predicateWithFormat:@"name = %@",@"2"];
        [cmd setPredicate:condition];
    
        NSArray *records = [context executeFetchRequest:cmd error:nil];
    
        if ([records count]>0) {
            NSManagedObject *rec = [records objectAtIndex:0];
        
            [context deleteObject:rec];
        
            [context save:nil];
        }
    }
    else
    {
        NSManagedObjectContext *context = [self managedObjectContext];
        NSEntityDescription *entity = [NSEntityDescription entityForName:@"CarStyle" inManagedObjectContext:context];
        NSFetchRequest *cmd = [[[NSFetchRequest alloc]init]autorelease];
        [cmd setEntity:entity];
        //设置查询条件
        NSPredicate *condition = [NSPredicate predicateWithFormat:@"color = %@",@"3"];
        [cmd setPredicate:condition];
    
        NSArray *records = [context executeFetchRequest:cmd error:nil];
    
        if ([records count]>0) {
            NSManagedObject *rec = [records objectAtIndex:0];
        
            [context deleteObject:rec];
        
            [context save:nil];
        }
    }
}

- (void)insert1VNData
{    
    
    NSManagedObject *main = [NSEntityDescription insertNewObjectForEntityForName:@"Company" inManagedObjectContext:self.managedObjectContext];
    [main setValue:@"OK" forKey:@"name"];
    
    NSManagedObject *dpt1 = [NSEntityDescription insertNewObjectForEntityForName:@"Department" inManagedObjectContext:self.managedObjectContext];
    [dpt1 setValue:@"A" forKey:@"deptName"];
    
    NSManagedObject *dpt2 = [NSEntityDescription insertNewObjectForEntityForName:@"Department" inManagedObjectContext:self.managedObjectContext];
    [dpt2 setValue:@"B" forKey:@"deptName"];
    
    
    [dpt1 setValue:main forKey:@"cmpy"];
    [dpt2 setValue:main forKey:@"cmpy"];

    
    [self.managedObjectContext save:nil];
}

- (void)delete1VNofNData
{
    NSManagedObjectContext *context = [self managedObjectContext];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Department" inManagedObjectContext:context];
    NSFetchRequest *cmd = [[[NSFetchRequest alloc]init]autorelease];
    [cmd setEntity:entity];
    //设置查询条件
    NSPredicate *condition = [NSPredicate predicateWithFormat:@"deptName = %@",@"A"];
    [cmd setPredicate:condition];
    
    NSArray *records = [context executeFetchRequest:cmd error:nil];
    
    if ([records count]>0) {
        NSManagedObject *rec = [records objectAtIndex:0];
        
        [context deleteObject:rec];
        
        [context save:nil];
    }
}

- (void)delete1VNof1Data
{
    NSManagedObjectContext *context = [self managedObjectContext];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Company" inManagedObjectContext:context];
    NSFetchRequest *cmd = [[[NSFetchRequest alloc]init]autorelease];
    [cmd setEntity:entity];
    //设置查询条件
    NSPredicate *condition = [NSPredicate predicateWithFormat:@"name = %@",@"OK"];
    [cmd setPredicate:condition];
    
    NSArray *records = [context executeFetchRequest:cmd error:nil];
    
    if ([records count]>0) {
        NSManagedObject *rec = [records objectAtIndex:0];
        
        [context deleteObject:rec];
        
        NSError* err;
        [context save:&err];
        
        if (!err)
        {
            NSLog(@"%@",[err localizedDescription]);
        }
    }    
}