详解iOS应用开发中Core Data数据存储的使用(2)-木庄网络博客

7.删除数据

代码如下:

/* 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

代码如下:

<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>
<pre></pre>


 

注意ascending:YES 属性决定排序顺序

标签：SQLite

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