我们接着上一篇 深入浅出MagicalRecord-02。
这节我们来一起学习下MagicalRecord对数据的增删改查，内容主要来自于 MagicalRecord的github资料。
1. 增-创建实体
Person *myPerson = [Person MR_createEntity];
Person *myPerson = [Person MR_createInContext:otherContext];
2. 删-删除实体
[myPerson MR_deleteEntity];
[myPerson MR_deleteInContext:otherContext];
[Person MR_truncateAll];
[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
NSArray *people = [Person MR_findAll];
NSArray *peopleSorted = [Person MR_findAllSortedBy:@"lastName" ascending:YES];
NSArray *peopleSorted = [Person MR_findAllSortedBy:@"lastName,firstName" ascending:YES];
NSArray *peopleSorted = [Person MR_findAllSortedBy:@"lastName:NO,firstName" ascending:YES];
//或者
NSArray *peopleSorted = [Person MR_findAllSortedBy:@"lastName,firstName:YES" ascending:NO];
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
NSNumber *count = [Person MR_numberOfEntities];
NSNumber *count = [Person MR_numberOfEntitiesWithPredicate:...];
+ (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];
