使用python从数据库获取数据(在Django框架上)

Question

通常，如果我为此编写一条sql语句，我会这样做，

    SELECT * FROM (django_baseaccount LEFT JOIN django_account ON django_baseaccount.user_id = django_account.baseaccount_ptr_id)
LEFT JOIN django_address ON django_account.baseaccount_ptr_id = django_address.user_id;name 

如何将其放入使用API查询数据库的Djagno方法中。

TradeDownloads.objects.filter(online=1)[:6]

我的模型基本帐户

class BaseAccount(models.Model):
user = models.ForeignKey(User, unique=True)

def __unicode__(self):
    """
    Return the unicode representation of this customer, which is the user's
    full name, if set, otherwise, the user's username
    """
    fn = self.user.get_full_name()
    if fn:
        return fn
    return self.user.username

def user_name(self):
    """
    Returns the full name of the related user object
    """
    return self.user.get_full_name()

def email(self):
    """
    Return the email address of the related user object
    """
    return self.user.email

账号

class Account(BaseAccount):
"""
The account is an extension of the Django user and serves as the profile
object in user.get_profile() for shop purchases and sessions
"""
telephone = models.CharField(max_length=32)
default_address = models.ForeignKey(Address, related_name='billing_account', blank=True, null=True)
security_question = models.ForeignKey(SecurityQuestion)
security_answer = models.CharField(max_length=200)
how_heard = models.CharField("How did you hear about us?", max_length=100)
feedback = models.TextField(blank=True)
opt_in = models.BooleanField("Subscribe to mailing list", help_text="Please tick here if you would like to receive updates from %s" % Site.objects.get_current().name)
temporary = models.BooleanField()

def has_placed_orders(self):
    """
    Returns True if the user has placed at least one order, False otherwise
    """
    return self.order_set.count() > 0

def get_last_order(self):
    """
    Returns the latest order that this customer has placed. If no orders
    have been placed, then None is returned
    """
    try:
        return self.order_set.all().order_by('-date')[0]
    except IndexError:
        return None

def get_currency(self):
    """
    Get the currency for this customer. If global currencies are enabled
    (settings.ENABLE_GLOBAL_CURRENCIES) then this function will return
    the currency related to their default address, otherwise, it returns
    the site default
    """
    if settings.ENABLE_GLOBAL_CURRENCIES:
        return self.default_address.country.currency
    return Currency.get_default_currency()
currency = property(get_currency)

def get_gateway_currency(self):
    """
    Get the currency that an order will be put through protx with. If protx
    currencies are enabled (settings.ENABLE_PROTX_CURRENCIES), then the
    currency will be the same returned by get_currency, otherwise, the
    site default is used
    """
    if settings.ENABLE_PROTX_CURRENCIES and settings.ENABLE_GLOBAL_CURRENCIES:
        return self.currency
    return Currency.get_default_currency()
gateway_currency = property(get_gateway_currency)

地址

class Address(models.Model):
"""
This class encapsulates the data required for postage and payment mechanisms
across the site. Each address is associated with a single store account
"""
trade_user = models.BooleanField("Are you a stockist of N  Products", help_text="Please here if you are a  Stockist")
company_name = models.CharField(max_length=32, blank=True)
line1 = models.CharField(max_length=200)
line2 = models.CharField(max_length=200, blank=True)
line3 = models.CharField(max_length=200, blank=True)
city = models.CharField(max_length=32)
county = models.CharField(max_length=32)
postcode = models.CharField(max_length=12)
country = models.ForeignKey(Country)
account = models.ForeignKey('Account')

class Meta:
    """
    Django meta options

    verbose_name_plural = "Addresses"
    """
    verbose_name_plural = "Addresses"

def __unicode__(self):
    """
    The unicode representation of this address, the postcode plus the county
    """
    return ', '.join((self.postcode, str(self.county)))

def line_list(self):
    """
    Return a list of all of this objects address lines that are not blank,
    in the natural order that you'd expect to see them. This is useful for
    outputting to a template with the aid of python String.join()
    """
    return [val for val in (self.line1, self.line2, self.line3, self.city, self.county, self.postcode, self.country.name) if val]

Answer 1

“通常情况下，如果我正在编写sql语句”

欢迎使用ORM。您不是在编写SQL，因此请从问题中删除这一点。永远不要发布SQL并询问如何将SQL转换为ORM。翻译SQL会限制您的学习能力。别再这么做了。

写下预期的结果。

看起来您正在获取所有的Account对象。句号。在视图函数或模板中的某些点上，您也希望获得一个Address。

for a in Account.objects.all():
    a.default_address # this is the address that SQL brought in via a "join".

就这样。请实际执行Django教程中的所有示例。实际输入示例中的代码，看看它是如何工作的。

所有的"join“操作都是SQL变通方法。它们是一种奇怪的SQL-ism，与底层对象无关。因此，停止使用SQL术语来描述您想要的内容。

Answer 2

对于复杂的查询，Django提供了一种干净的方法来回退到原生SQL，请参阅官方文档：Performing raw SQL queries

Answer 3

忘了SQL吧。您希望通过此查询实现什么目标？您想对结果做什么？

你还没有发布你的模型。它们是否定义了外键？你能不能只做一个简单的查询，然后使用select_related()来获取连接的对象？

已编辑以添加给定the previous time you asked this question的答案有什么问题

再次编辑了，但每个人都向你展示了如何通过外键获取项目！忘了id吧，你不需要它。如果您有一个Account对象a，只需执行a.default_address即可获得相关的实际Address对象。如果这不起作用，那么您没有发布正确的模型，因为这肯定会与您发布的模型一起工作。