Question

我刚开始使用django查询语言，但遇到了一些困难。我希望方法 get_present_users（）使用“Presence”对象返回连接到某个Drink对象的所有用户。我知道我可以通过以下方式获取所有相关的状态对象：

Presence.objects.filter(event=self.pk)

但是，我无法想到将此查询集转换为所有用户的方法。你能帮助我一个人吗？

class Drink(BaseModel):
    date = models.DateField()
    comments = models.TextField(blank=True)

class Presence(BaseModel):
    event = models.ForeignKey(Drink)
    submitted_by = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='presence_submitted_by')
    present_user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='presence_present_user')

Answer 1

如果您正在尝试编写一个函数，该函数可以获取Users对象Drink与Presence Presence关联的所有Users而不是试图去来自from django.contrib.auth.models import User ... class Drink(model.Models): ... def get_present_users(self): return User.objects.filter(presence_present_user__event=self) ...并获取drink = Drink.objects.get(id=1) print(drink.get_present_users()) >> [<User: >, <User: >]的列表。

@interface MyView : UIView

@end

@implementation MyView

- (instancetype)init
{
    if (self = [super init]) {
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(changeOrientationHandler:) name:UIApplicationWillChangeStatusBarOrientationNotification object:nil];
    }
    return self;
}

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationWillChangeStatusBarOrientationNotification object:nil];
}

- (void)updateTransformWithOrientation:(UIInterfaceOrientation)orientation
{
    CGFloat width = CGRectGetWidth(self.window.bounds);
    CGFloat height = CGRectGetHeight(self.window.bounds);
    if (width > height) {
        CGFloat temp = width;
        width = height;
        height = temp;
    }
    CGFloat offset = (height - width) / 2;
    CGAffineTransform transform;
    switch (orientation) {
        case UIInterfaceOrientationLandscapeLeft:
            transform = CGAffineTransformMakeTranslation(-offset, offset);
            transform = CGAffineTransformRotate(transform, -M_PI_2);
            break;
        case UIInterfaceOrientationLandscapeRight:
            transform = CGAffineTransformMakeTranslation(-offset, offset);
            transform = CGAffineTransformRotate(transform, M_PI_2);
            break;
        case UIInterfaceOrientationPortraitUpsideDown:
            transform = CGAffineTransformMakeRotation(-M_PI);
            break;
        default:
            transform = CGAffineTransformIdentity;
            break;
    }
    self.transform = transform;
    self.frame = CGRectMake(0, 0, width, height);
}

- (void)updateFrameWithOrientation:(UIInterfaceOrientation)orientation
{
    CGFloat width = CGRectGetWidth(self.window.bounds);
    CGFloat height = CGRectGetHeight(self.window.bounds);
    if (width > height) {
        CGFloat temp = width;
        width = height;
        height = temp;
    }
    switch (orientation) {
        case UIInterfaceOrientationLandscapeLeft:
        case UIInterfaceOrientationLandscapeRight:
            self.frame = CGRectMake(0, 0, height, width);
            break;
        default:
            self.frame = CGRectMake(0, 0, width, height);
            break;
    }
}

- (void)updateWithOrientation:(UIInterfaceOrientation)orientation
{
    BOOL isIos7 = [[UIDevice currentDevice].systemVersion floatValue] < 8.0;
    BOOL isKeyboardWindow = [self.window isKindOfClass:NSClassFromString(@"UITextEffectsWindow")];
    if (isIos7 == YES && isKeyboardWindow == NO) {
        [self updateTransformWithOrientation:orientation];
    } else {
        [self updateFrameWithOrientation:orientation];
    }
}

- (void)changeOrientationHandler:(NSNotification *)notification
{
    [UIView animateWithDuration:0.25 animations:^{
        UIInterfaceOrientation orientation = (UIInterfaceOrientation)[notification.userInfo[UIApplicationStatusBarOrientationUserInfoKey] integerValue];
        [self updateWithOrientation:orientation];
    }];
}

@end

这将允许你写：

dplyr

使用django查询语言查询连接的对象

1 个答案: