1. 增-创建实体
创建实体
Person *myPerson = [Person MR_createEntity];
指定创建的上下文中创建实体
Person *myPerson = [Person MR_createInContext:otherContext];
2. 删-删除实体
删除一个实体
[myPerson MR_deleteEntity];
删除特定上下文中的实体
[myPerson MR_deleteInContext:otherContext];
删除所有实体
[Person MR_truncateAll];
删除特定上下文中的所有实体
[Person MR_truncateAllInContext:otherContext];
3. 改-修改实体
Person *person = ...;
person.lastname = "xxx";
4. 查-查询实体
查询的结果通常会返回一个NSArray结果。
a) 基本查询
从持久化存储（PersistantStore）中查询出所有的Person实体
NSArray *people = [Person MR_findAll];
查询出所有的Person实体并按照 lastName 升序（ascending）排列
NSArray *peopleSorted = [Person MR_findAllSortedBy:@"lastName" ascending:YES];
查询出所有的Person实体并按照 lastName 和 firstName 升序（ascending）排列
NSArray *peopleSorted = [Person MR_findAllSortedBy:@"lastName,firstName" ascending:YES];
查询出所有的Person实体并按照 lastName 降序，firstName 升序（ascending）排列
NSArray *peopleSorted = [Person MR_findAllSortedBy:@"lastName:NO,firstName" ascending:YES];
//或者
NSArray *peopleSorted = [Person MR_findAllSortedBy:@"lastName,firstName:YES" ascending:NO];
查询出所有的Person实体 firstName 为 Forrest 的实体
Person *person = [Person MR_findFirstByAttribute:@"firstName" withValue:@"Forrest"];
b) 高级查询
使用NSPredicate来实现高级查询。
NSPredicate *peopleFilter = [NSPredicate predicateWithFormat:@"department IN %@", @[dept1, dept2]];
NSArray *people = [Person MR_findAllWithPredicate:peopleFilter];
c)返回 NSFetchRequest
NSPredicate *peopleFilter = [NSPredicate predicateWithFormat:@"department IN %@", departments];
NSFetchRequest *people = [Person MR_requestAllWithPredicate:peopleFilter];
d)自定义 NSFetchRequest
NSPredicate *peopleFilter = [NSPredicate predicateWithFormat:@"department IN %@", departments];
NSFetchRequest *peopleRequest = [Person MR_requestAllWithPredicate:peopleFilter];
[peopleRequest setReturnsDistinctResults:NO];
[peopleRequest setReturnPropertiesNamed:@[@"firstName", @"lastName"]];
NSArray *people = [Person MR_executeFetchRequest:peopleRequest];
e)查询实体的个数
返回的是 NSNumber 类型
NSNumber *count = [Person MR_numberOfEntities];
基于NSPredicate查询条件过滤后的实体个数
NSNumber *count = [Person MR_numberOfEntitiesWithPredicate:...];
返回的是 NSUInteger 类型
+ (NSUInteger) MR_countOfEntities;
+ (NSUInteger) MR_countOfEntitiesWithContext:(NSManagedObjectContext *)context;
+ (NSUInteger) MR_countOfEntitiesWithPredicate:(NSPredicate *)searchFilter;
+ (NSUInteger) MR_countOfEntitiesWithPredicate:(NSPredicate *)searchFilter inContext:(NSManagedObjectContext *)
f)合计操作
NSInteger totalFat = [[CTFoodDiaryEntry MR_aggregateOperation:@"sum:" onAttribute:@"fatCalories" withPredicate:predicate] integerValue];
NSInteger fattest = [[CTFoodDiaryEntry MR_aggregateOperation:@"max:" onAttribute:@"fatCalories" withPredicate:predicate] integerValue];
NSArray *caloriesByMonth = [CTFoodDiaryEntry MR_aggregateOperation:@"sum:" onAttribute:@"fatCalories" withPredicate:predicate groupBy:@"month"];
g)从指定上下文中查询
NSArray *peopleFromAnotherContext = [Person MR_findAllInContext:someOtherContext];
Person *personFromContext = [Person MR_findFirstByAttribute:@"lastName" withValue:@"Gump" inContext:someOtherContext];
NSUInteger count = [Person MR_numberOfEntitiesWithContext:someOtherContext];
貌似该库中没有嵌套查询，多条件查询。
