CoreData使用笔记

1. 重要概念

1) Entity  (NSEntityDescription)

    对应数据库中的表  

NSEntityDescription  *userEntity  =  
[[[NSEntityDescription  alloc]  init]  autorelease];  
[userEntity  setName:@"User"]; 

2) Propery (NSAttributeDescription)

    Entity的列

NSAttributeDescription  *nameAttribute;  
nameAttribute  =  [[[NSAttributeDescription  alloc]  init]  autorelease];  
[nameAttribute  setName:@"name"];  
[nameAttribute  setAttributeType:NSStringAttributeType];  
[nameAttribute  setOptional:NO];  

把属性和表关联：

[userEntity  setProperties:  
[NSArray  arrayWithObjects:  dobAttribute,  nameAttribute,  nil]];  

2) Managed Object Model (NSManagedObjectModel)

    相当于数据库里的schema (什么是schema，请百度下)

3) Managed Object Context (NSManagedObjectContext)

    相当于数据库中的表

4) Managed Object

    相当于数据库的行。

5) Persistent Store coordinator

   

2. Core Data 的 CRUD操作

 1) Create

 例子：插入一条新的记录

-(BOOL)addUser:(NSString*)  _userName  dateOfBirth:(NSDate*)_dob  
    andSocial:(NSString*)_social
{  
    User  *user  =  (User  *)[NSEntityDescription  
    insertNewObjectForEntityForName:@"User"  
    inManagedObjectContext:self.managedObjectContext];  
    user.dob  =  _dob;  
    user.name  =  _userName;  
    user.social  =  _social;  
    return  [self.managedObjectContext save:NULL];  
}  

 2) Delete

[self.managedObjectContext  deleteObject:user];  
[self.managedObjectContext  save:NULL];  

3) Read and update

   i) 无条件的Fetch

-(NSArray*)allUsers{  
    NSFetchRequest  *request  =  
    [[[NSFetchRequest  alloc]  init]  autorelease];  
    NSEntityDescription  *entity  =  
    [NSEntityDescription  entityForName:@"User" inManagedObjectContext:self.managedObjectContext];  
    [request  setEntity:entity];  
    return  [self.managedObjectContext executeFetchRequest:request  error:NULL];  
} 

   ii) 有条件的Fetch

-(NSArray*)usersWithNameQuery:(NSString*)_query
{  
    NSFetchRequest  *request  =  [[[NSFetchRequest  alloc]  init]  autorelease];  
    NSEntityDescription  *entity  =  
    [NSEntityDescription entityForName:@"User" inManagedObjectContext:self.managedObjectContext];  
    [request  setEntity:entity];  
    NSPredicate *predicate = [NSPredicate  predicateWithFormat:@"name  like[cd]  %@",  [NSString  stringWithFormat:@"*%@*",  _query]];  
    [request setPredicate:predicate];  
    return  [self.managedObjectContext executeFetchRequest:request  error:NULL];  
}  

  iii) 排序Fetch

-(NSArray*)allUsersSorted
{  
    NSFetchRequest  *request  =  [[[NSFetchRequest  alloc]  init]  autorelease];  
    NSEntityDescription  *entity  =  
    [NSEntityDescription  entityForName:@"User"  
    inManagedObjectContext:self.managedObjectContext];  
    [request  setEntity:entity];  
    NSSortDescriptor  *sortDescriptor  =  
    [[[NSSortDescriptor  alloc]  initWithKey:@"dob"  ascending:NO]  
    autorelease];  
    [request  setSortDescriptors:  
    [NSArray  arrayWithObject:sortDescriptor]];  
    return  [self.managedObjectContext executeFetchRequest:request  error:NULL];  
}