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2 个实体： 用户和建筑物。

用户有一个名为building的NSSet类型的属性

我想通过属性guid从NSSet检索Buildings实体。

在应用程序第一次运行时，添加数据成功。可以正确检索和显示数据。应用程序关闭后，随后通过 guid 获取现有建筑物实体的尝试失败。第一次getBuildingsByGuid返回nil，因为没有实体；当我调用函数getBuildingsByGuid并且建筑物集中有实体时，应用程序崩溃。使用谓词作品获取；实体之间的关系是：一个用户对许多建筑物。

无法通过调试捕获指令。

在User对象中，以下自定义方法应获取Buildings：

- (Buildings *)getBuildingsByGuid:(NSString *)guid
{
    for (Buildings *buildings in self.buildings)
    {
        if ([buildings.guid isEqualToString:guid])
            return buildings;
    }
    return nil;
}

编辑：我的实体用户标头包含：

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>

@class Buildings, TableBuildings;

@interface User : NSManagedObject

@property (nonatomic, retain) NSString * email;
@property (nonatomic, retain) NSString * first_name;
@property (nonatomic, retain) NSString * guid_contact;
@property (nonatomic, retain) NSString * guid_user;
@property (nonatomic, retain) NSString * guid_userRole;
@property (nonatomic, retain) NSString * last_name;
@property (nonatomic, retain) NSString * password;
@property (nonatomic, retain) NSString * role_code;
@property (nonatomic, retain) NSString * role_name;
@property (nonatomic, retain) NSString * token;
@property (nonatomic, retain) NSString * type_code;
@property (nonatomic, retain) NSString * type_name;
@property (nonatomic, retain) NSSet *buildings;
@property (nonatomic, retain) NSSet *tableBuildings;

@end

@interface User (CoreDataGeneratedAccessors)

// Buildings
- (void)addBuildingsObject:(Buildings *)value;
- (void)removeBuildingsObject:(Buildings *)value;
- (void)addBuildings:(NSSet *)values;
- (void)removeBuildings:(NSSet *)values;
- (BOOL)containsBuildingsObject:(Buildings*)value;
- (Buildings *)getBuildingsByGuid:(NSString *)guid;

// TableBuildings
- (void)addTableBuildingsObject:(TableBuildings *)value;
- (void)removeTableBuildingsObject:(TableBuildings *)value;
- (void)addTableBuildings:(NSSet *)values;
- (void)removeTableBuildings:(NSSet *)values;
- (BOOL)containsTableBuildingsObject:(TableBuildings*)value;
- (TableBuildings *)getTableBuildingsByGuid:(NSString *)guid;

@end

实现文件：

#import "User.h"
#import "Buildings.h"
#import "TableBuildings.h"


@implementation User

@dynamic email;
@dynamic first_name;
@dynamic guid_contact;
@dynamic guid_user;
@dynamic guid_userRole;
@dynamic last_name;
@dynamic password;
@dynamic role_code;
@dynamic role_name;
@dynamic token;
@dynamic type_code;
@dynamic type_name;
@dynamic buildings;
@dynamic tableBuildings;

@end

@implementation User (CoreDataGeneratedAccessors)

#pragma mark - Buildings management methods

- (void)addBuildingsObject:(Buildings *)value
{
    NSSet *changedObjects = [[NSSet alloc] initWithObjects:&value count:1];
    [self willChangeValueForKey:@"buildings" withSetMutation:NSKeyValueUnionSetMutation usingObjects:changedObjects];
    [[self primitiveValueForKey:@"buildings"] addObject:value];
    [self didChangeValueForKey:@"buildings" withSetMutation:NSKeyValueUnionSetMutation usingObjects:changedObjects];
    [changedObjects release];
}

- (void)removeBuildingsObject:(Buildings *)value
{
    NSSet *changedObjects = [[NSSet alloc] initWithObjects:&value count:1];
    [self willChangeValueForKey:@"buildings" withSetMutation:NSKeyValueMinusSetMutation usingObjects:changedObjects];
    [[self primitiveValueForKey:@"buildings"] removeObject:value];
    [self didChangeValueForKey:@"buildings" withSetMutation:NSKeyValueMinusSetMutation usingObjects:changedObjects];
    [changedObjects release];
}

- (void)addBuildings:(NSSet *)values
{
    [self willChangeValueForKey:@"buildings" withSetMutation:NSKeyValueUnionSetMutation usingObjects:values];
    [[self primitiveValueForKey:@"buildings"] unionSet:values];
    [self didChangeValueForKey:@"buildings" withSetMutation:NSKeyValueUnionSetMutation usingObjects:values];
}

- (void)removeBuildings:(NSSet *)values
{
    [self willChangeValueForKey:@"buildings" withSetMutation:NSKeyValueUnionSetMutation usingObjects:values];
    [[self primitiveValueForKey:@"buildings"] unionSet:values];
    [self didChangeValueForKey:@"buildings" withSetMutation:NSKeyValueUnionSetMutation usingObjects:values];
}

- (BOOL) containsBuildingsObject:(Buildings*)value
{
    for (Buildings *buildings in self.buildings)
    {
        if( [buildings.guid isEqualToString:value.guid])
            return YES;
    }
    return NO;
}

- (Buildings *)getBuildingsByGuid:(NSString *)guid
{
    for (Buildings *buildings in self.buildings)
    {
        if ([buildings.guid isEqualToString:guid])
            return buildings;
    }
    return nil;
}

#pragma mark - TableBuildings management methods

- (void)addTableBuildingsObject:(TableBuildings *)value
{
    NSSet *changedObjects = [[NSSet alloc] initWithObjects:&value count:1];
    [self willChangeValueForKey:@"tableBuildings" withSetMutation:NSKeyValueUnionSetMutation usingObjects:changedObjects];
    [[self primitiveValueForKey:@"tableBuildings"] addObject:value];
    [self didChangeValueForKey:@"tableBuildings" withSetMutation:NSKeyValueUnionSetMutation usingObjects:changedObjects];
    [changedObjects release];
}

- (void)removeTableBuildingsObject:(TableBuildings *)value
{
    NSSet *changedObjects = [[NSSet alloc] initWithObjects:&value count:1];
    [self willChangeValueForKey:@"tableBuildings" withSetMutation:NSKeyValueMinusSetMutation usingObjects:changedObjects];
    [[self primitiveValueForKey:@"tableBuildings"] removeObject:value];
    [self didChangeValueForKey:@"tableBuildings" withSetMutation:NSKeyValueMinusSetMutation usingObjects:changedObjects];
    [changedObjects release];
}

- (void)addTableBuildings:(NSSet *)values
{
    [self willChangeValueForKey:@"tableBuildings" withSetMutation:NSKeyValueUnionSetMutation usingObjects:values];
    [[self primitiveValueForKey:@"tableBuildings"] unionSet:values];
    [self didChangeValueForKey:@"tableBuildings" withSetMutation:NSKeyValueUnionSetMutation usingObjects:values];
}

- (void)removeTableBuildings:(NSSet *)values
{
    [self willChangeValueForKey:@"tableBuildings" withSetMutation:NSKeyValueUnionSetMutation usingObjects:values];
    [[self primitiveValueForKey:@"tableBuildings"] unionSet:values];
    [self didChangeValueForKey:@"tableBuildings" withSetMutation:NSKeyValueUnionSetMutation usingObjects:values];
}

-(BOOL) containsTableBuildingsObject:(TableBuildings*)value
{
    for (TableBuildings *tableBuildings in self.tableBuildings)
    {
        if( [tableBuildings.guid_building isEqualToString:value.guid_building])
            return YES;
    }
    return NO;
}

- (TableBuildings *)getTableBuildingsByGuid:(NSString *)guid
{
    for (TableBuildings *tableBuildings in self.tableBuildings)
    {
        if ([tableBuildings.guid_building isEqualToString:guid])
            return tableBuildings;
    }
    return nil;
}

@结尾

当应用程序启动时，将通过电子邮件和密码获取用户：

user = [[DataController instance] fetchEntityOfType:object_User withPredicate:@"email = %@ AND password = %@", username, passwordMD5];

稍后，当我想显示我的建筑物列表时，我调用 getBuildingsByGuid 方法，如下所示：

// buildings is parsed from json and have NSDictionary type
for (NSDictionary *building in buildings)
    {
        NSString *guid_building = [building safeObjectForKey:@"guid"];

        // get building and check if is associated to the current user
        BuildingPerUser *buildingPerUser = [[DataController instance] fetchEntityOfType:object_BuildingPerUser withPredicate:@"guid_user = %@ AND guid_building = %@", guid_user, guid_building];

        //create new association if not exists
        if (!buildingPerUser)
        {
            buildingPerUser = [[[DataController instance] newEnityOfType:object_BuildingPerUser] autorelease];
            buildingPerUser.guid_user = guid_user;
            buildingPerUser.guid_building = guid_building;
        }

        Buildings *buildingRow = [user getBuildingsByGuid:guid_building];

        // create new building if not exists
        if (!buildingRow)
        {
            buildingRow = [[[DataController instance] newEnityOfType:object_Buildings] autorelease];
            buildingRow.guid = guid_building;
            [user addBuildingsObject:buildingRow];
        }

        // update building
        buildingRow.name = [building safeObjectForKey:@"name"];
        buildingRow.isNew = [NSNumber numberWithBool:NO];

        [delComplementBuildings addObject:guid_building];
    }

如果我使用： 

Buildings *buildingRow = [[DataController instance] fetchEntityOfType:object_Buildings withPredicate:@"guid = %@", guid_building];

...我的应用程序工作。和：

Buildings *buildingRow = [user getBuildingsByGuid:guid_building];

..应用程序崩溃。

我更喜欢使用对象而不是谓词获取......

另一个编辑：我发现了异常：关于建筑物的 nsset 实体的关系错误 下面是建筑物的列表：

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>

@class TableBuildings, User;

@interface Buildings : NSManagedObject

@property (nonatomic, retain) NSString * guid;
@property (nonatomic, retain) NSNumber * isNew;
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) NSSet *tableBuildings;
@property (nonatomic, retain) User *user;
@end

@interface Buildings (CoreDataGeneratedAccessors)

- (void)addTableBuildingsObject:(TableBuildings *)value;
- (void)removeTableBuildingsObject:(TableBuildings *)value;
- (void)addTableBuildings:(NSSet *)values;
- (void)removeTableBuildings:(NSSet *)values;
@end

#import "Buildings.h"
#import "TableBuildings.h"
#import "User.h"


@implementation Buildings

@dynamic guid;
@dynamic isNew;
@dynamic name;
@dynamic tableBuildings;
@dynamic user;

@end

建筑物访问器尚未实施。

问题已解决。初始化用户时出错。解决方案：为用户使用属性。

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