oreData的学习记录
1.如果想创建一个带有coreData的程序,要在项目初始化的时候勾选中
2.创建完成之后,会发现在AppDelegate里多出了几个属性,和2个方法
- <span style="font-size:18px;">
- @property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
- @property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;
- @property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;
- - (void)saveContext;
- - (NSURL *)applicationDocumentsDirectory;</span>
managedObjectContext (被管理的数据上下文)操作实际内容(操作持久层)作用:插入数据,查询数据,删除数据
NSManagedObjectModel(被管理的数据模型)数据库所有表格或数据结构,包含各实体的定义信息 作用:添加实体的属性,建立属性之间的关系操作方法:视图编辑器,或代码
NSPersistentStoreCoordinator(持久化存储助理)相当于数据库的连接器 作用:设置数据存储的名字,位置,存储方式,和存储时机
方法saveContext表示:保存数据到持久层(数据库)
方法applicationDocumentsDirectory表示:应用程序沙箱下的Documents目录路径
3.如果想创建一个实体对象的话,需要点击.xcdatamodel,Add Entity,添加想要的字段
4.生成对象文件,command+n,然后选中CoreData里的NSManagerObjectSubClass进行关联,选中实体创建
5.添加数据
- Person *newPerson = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:self.managedObjectContext];
- if (newPerson == nil){
- NSLog(@"Failed to create the new person.");
- return NO;
- }
- newPerson.firstName = paramFirstName;
- newPerson.lastName = paramLastName;
- newPerson.age = [NSNumber numberWithUnsignedInteger:paramAge];
- NSError *savingError = nil;
- if ([self.managedObjectContext save:&savingError]){
- return YES;
- } else {
- NSLog(@"Failed to save the new person. Error = %@", savingError);
- }
NSEntityDescription(实体结构)相当于表格结构
6.取出数据查询
- /* Create the fetch request first */
- NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
- /* Here is the entity whose contents we want to read */
- NSEntityDescription *entity =
- [NSEntityDescription
- entityForName:@"Person"
- inManagedObjectContext:self.managedObjectContext];
- /* Tell the request that we want to read the
- contents of the Person entity */
- [fetchRequest setEntity:entity];
- NSError *requestError = nil;
- /* And execute the fetch request on the context */
- NSArray *persons =
- [self.managedObjectContext executeFetchRequest:fetchRequest
- error:&requestError];
- /* Make sure we get the array */
- if ([persons count] > 0){
- /* Go through the persons array one by one */
- NSUInteger counter = 1;
- for (Person *thisPerson in persons){
- NSLog(@"Person %lu First Name = %@",
- (unsigned long)counter,
- thisPerson.firstName);
- NSLog(@"Person %lu Last Name = %@",
- (unsigned long)counter,
- thisPerson.lastName);
- NSLog(@"Person %lu Age = %ld",
- (unsigned long)counter,
- (unsigned long)[thisPerson.age unsignedIntegerValue]);
- counter++;
- }
- } else {
- NSLog(@"Could not find any Person entities in the context.");
- }
7.删除数据
- /* Create the fetch request first */
- NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
- /* Here is the entity whose contents we want to read */
- NSEntityDescription *entity =
- [NSEntityDescription
- entityForName:@"Person"
- inManagedObjectContext:self.managedObjectContext];
- /* Tell the request that we want to read the
- contents of the Person entity */
- [fetchRequest setEntity:entity];
- NSError *requestError = nil;
- /* And execute the fetch request on the context */
- NSArray *persons =
- [self.managedObjectContext executeFetchRequest:fetchRequest
- error:&requestError];
- if ([persons count] > 0){
- /* Delete the last person in the array */
- Person *lastPerson = [persons lastObject];
- [self.managedObjectContext deleteObject:lastPerson];
- NSError *savingError = nil;
- if ([self.managedObjectContext save:&savingError]){
- NSLog(@"Successfully deleted the last person in the array.");
- } else {
- NSLog(@"Failed to delete the last person in the array.");
- }
- } else {
- NSLog(@"Could not find any Person entities in the context.");
- }
8.排序
- <pre code_snippet_id="243955" snippet_file_name="blog_20140319_5_4289257" name="code" class="objc">NSSortDescriptor *ageSort =
- [[NSSortDescriptor alloc] initWithKey:@"age"
- ascending:YES];
- NSSortDescriptor *firstNameSort =
- [[NSSortDescriptor alloc] initWithKey:@"firstName"
- ascending:YES];
- NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:
- ageSort,
- firstNameSort, nil nil];
- fetchRequest.sortDescriptors = sortDescriptors; </pre><p></p>
- <pre></pre>
- <p></p>
- <p style="background-color:rgb(255,255,255); margin:10px auto; padding-top:0px; padding-bottom:0px; font-family:verdana,'ms song',Arial,Helvetica,sans-serif; line-height:19.09090805053711px">
- <span style="background-color:rgb(255,255,255)"><span style="font-size:18px"><br>
- </span></span></p>
- <span style="background-color:rgb(255,255,255)">注意</span><span style="font-size:18px; background-color:rgb(255,255,255)">ascending:YES 属性决定排序顺序</span><span style="background-color:rgb(255,255,255)"><span style="font-size:18px"><br>
- <br>
- <br>
- </span></span><br>