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
创建实体1
| Person *myPerson = [Person MR_createEntity];
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指定创建的上下文中创建实体1
| Person *myPerson = [Person MR_createInContext:otherContext];
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2. 删-删除实体
删除一个实体1
| [myPerson MR_deleteEntity];
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删除特定上下文中的实体1
| [myPerson MR_deleteInContext:otherContext];
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删除所有实体1
| [Person MR_truncateAll];
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删除特定上下文中的所有实体1
| [Person MR_truncateAllInContext:otherContext];
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3. 改-修改实体
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| Person *person = ...;
person.lastname = "xxx";
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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1
| NSArray *people = [Person MR_findAll];
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查询出所有的Person实体并按照 lastName 升序（ascending）排列1
| NSArray *peopleSorted = [Person MR_findAllSortedBy:@"lastName" ascending:YES];
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查询出所有的Person实体并按照 lastName 和 firstName 升序（ascending）排列1
| NSArray *peopleSorted = [Person MR_findAllSortedBy:@"lastName,firstName" ascending:YES];
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查询出所有的Person实体并按照 lastName 降序，firstName 升序（ascending）排列1
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| NSArray *peopleSorted = [Person MR_findAllSortedBy:@"lastName:NO,firstName" ascending:YES];
NSArray *peopleSorted = [Person MR_findAllSortedBy:@"lastName,firstName:YES" ascending:NO];
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查询出所有的Person实体 firstName 为 Forrest 的实体1
| Person *person = [Person MR_findFirstByAttribute:@"firstName" withValue:@"Forrest"];
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b) 高级查询
使用NSPredicate来实现高级查询。
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| NSPredicate *peopleFilter = [NSPredicate predicateWithFormat:@"department IN %@", @[dept1, dept2]];
NSArray *people = [Person MR_findAllWithPredicate:peopleFilter];
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c)返回 NSFetchRequest
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| NSPredicate *peopleFilter = [NSPredicate predicateWithFormat:@"department IN %@", departments];
NSFetchRequest *people = [Person MR_requestAllWithPredicate:peopleFilter];
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d)自定义 NSFetchRequest
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| 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];
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e)查询实体的个数
返回的是 NSNumber 类型1
| NSNumber *count = [Person MR_numberOfEntities];
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基于NSPredicate查询条件过滤后的实体个数1
| NSNumber *count = [Person MR_numberOfEntitiesWithPredicate:...];
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返回的是 NSUInteger 类型1
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| + (NSUInteger) MR_countOfEntities;
+ (NSUInteger) MR_countOfEntitiesWithContext:(NSManagedObjectContext *)context;
+ (NSUInteger) MR_countOfEntitiesWithPredicate:(NSPredicate *)searchFilter;
+ (NSUInteger) MR_countOfEntitiesWithPredicate:(NSPredicate *)searchFilter inContext:(NSManagedObjectContext *)
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f)合计操作
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| 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"];
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g)从指定上下文中查询
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| NSArray *peopleFromAnotherContext = [Person MR_findAllInContext:someOtherContext];
Person *personFromContext = [Person MR_findFirstByAttribute:@"lastName" withValue:@"Gump" inContext:someOtherContext];
NSUInteger count = [Person MR_numberOfEntitiesWithContext:someOtherContext];
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