Question

我有Django模型：

class Species(models.Model):
    species_id = models.IntegerField(db_column='Species ID', primary_key=True)
    name = models.CharField(db_column='Name', max_length=100)



class Status(models.Model):
    species_id = models.ForeignKey(Species, db_column='Species ID', primary_key=True)
    protected = models.NullBooleanField(db_column='Protected')

class Images(models.Model):
    species_id = models.ForeignKey('Species', db_column='Species ID')
    url = models.CharField(db_column='URL', max_length=719)

有没有办法在不使用原始SQL的情况下执行以下SQL查询。

SELECT Name, URL FROM Images i 
INNER JOIN Species s USING (`Species ID`) 
INNER JOIN Status st USING (`Species ID`) 
WHERE `st`.`Protected` = TRUE

Answer 1

这就是我重构代码的方式：

class Species(models.Model):
    name = models.CharField(db_column='Name', max_length=100)

class Status(models.Model):
    species = models.ForeignKey(Species, db_column='Species ID', primary_key=True)
    protected = models.NullBooleanField(db_column='Protected')

class Images(models.Model):
    species = models.ForeignKey('Species', db_column='Species ID')
    url = models.CharField(db_column='URL', max_length=719)

然后我会这样做：

protected_species = Status.objects
                    .filter(protected=True)
                    .values_list('species_id', flat=True)
Images.objects.filter(species_id__in=protected_species)
              .values('url','species__name')

但正如@Maxime Lorant所说，我觉得你的模特很眩目。

Answer 2

如果您稍微更改模型，可以执行以下操作：

images = Images.objects.filter(species__status__protected=True)

更新模型：

class Species(models.Model):
    name = models.CharField(max_length=100)

class Status(models.Model):
    species = models.ForeignKey('Species', primary_key=True)
    protected = models.NullBooleanField()

class Images(models.Model):
    species = models.ForeignKey('Species')
    url = models.CharField(max_length=719)

Answer 3

您的数据库结构首先是破碎的。我想每个Species对象只有一个状态，所以你不需要有3个模型。有2个型号，您可以执行以下操作：

class Species(models.Model):
    species_id = models.IntegerField(db_column='Species ID', primary_key=True)
    name = models.CharField(db_column='Name', max_length=100)
    protected = models.NullBooleanField(db_column='Protected')


class Images(models.Model):
    species = models.ForeignKey('Species', db_column='Species ID')
    url = models.CharField(db_column='URL', max_length=719)

# query
data = Images.objects.filter(species__protected=True).values('url', 'species__name')

Django模型中的多个连接

3 个答案: