深入浅出MagicalRecord-03

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

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];

删除指定上下文中的实体

[myPerson MR_deleteInContext:otherContext];

删除所有实体

[Person MR_truncateAll];

删除指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,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升序,firstName降序(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,lastName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NSUInterger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];