1.如果想創建一個帶有coreData的程序,要在項目初始化的時候勾選中
2.創建完成之后,會發現在AppDelegate里多出了幾個屬性,和2個方法
復制代碼代碼如下:
<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>
Core Data數據持久化是對SQLite的一個升級，它是ios集成的，在說Core Data之前，我們先說說在CoreData中使用的幾個類。
（1）NSManagedObjectModel(被管理的對象模型)
相當于實體，不過它包含 了實體間的關系
(2)NSManagedObjectContext(被管理的對象上下文)
操作實際內容
作用：插入數據 查詢 更新 刪除
（3）NSPersistentStoreCoordinator(持久化存儲助理)
相當于數據庫的連接器
(4)NSFetchRequest(獲取數據的請求)
相當于查詢語句
(5)NSPredicate(相當于查詢條件)
(6)NSEntityDescription(實體結構)
(7)后綴名為.xcdatamodel的包
里面的.xcdatamodel文件，用數據模型編輯器編輯
編譯后為.momd或.mom文件，這就是為什么文件中沒有這個東西，而我們的程序中用到這個東西而不會報錯的原因。
3.如果想創建一個實體對象的話,需要點擊.xcdatamodel,Add Entity,添加想要的字段
4.生成對象文件,command+n,然后選中CoreData里的NSManagerObjectSubClass進行關聯,選中實體創建
5.添加數據
復制代碼代碼如下:
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（實體結構）相當于表格結構
6.取出數據查詢
復制代碼代碼如下:
/* 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.刪除數據
復制代碼代碼如下:
/* 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
復制代碼代碼如下:
<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>
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<span style="background-color:rgb(255,255,255)">注意</span><span style="font-size:18px; background-color:rgb(255,255,255)">ascending:YES 屬性決定排序順序</span><span style="background-color:rgb(255,255,255)"><span style="font-size:18px"><br>
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