视图上的 Django 外键
我正在从现有数据库构建 django 应用程序。无论好坏，我有一些观点，我想将它们作为我的模型的基础。它们看起来像这样：
class Device(Model):
id = models.IntegerField( primary_key=True, db_column='node_id' )
name = models.CharField(max_length=127, db_column='node' )
class Meta:
db_table = 'node' # db view
managed = False
class Entity(Model):
id = models.IntegerField( primary_key=True, db_column='_id' )
device = models.ForeignKey(Device, db_column='node_id' )
class Meta:
db_table = 'entity' # db view
managed = Fase
所以一切正常。但是，当我尝试使用利用外键的模板时，速度非常慢：
{% for e in entities %}
{{ e.device.name }}
{% endfor %}
查看日志，它似乎正在重复查询每个“node_id”，并最终超时。
（当然，如果我不包含e.device.name一切都很快）
有没有办法可以优化这个？
公平地说，“实体”视图已经将设备名称作为另一个字段（节点），因此我可以使用它，但我希望存在这种关系。
i'm building a django app from an existing database. for better or worse, i have a couple of views that i would like to base my models off. they look something like this:
class Device(Model):
id = models.IntegerField( primary_key=True, db_column='node_id' )
name = models.CharField(max_length=127, db_column='node' )
class Meta:
db_table = 'node' # db view
managed = False
class Entity(Model):
id = models.IntegerField( primary_key=True, db_column='_id' )
device = models.ForeignKey(Device, db_column='node_id' )
class Meta:
db_table = 'entity' # db view
managed = Fase
so things work okay. however, when i try to use a template that utilises the ForeignKey it is very slow:
{% for e in entities %}
{{ e.device.name }}
{% endfor %}
looking at the logs, it appears to be repeating queries for each 'node_id', and ultimately timeout out.
(of course, if i do not include e.device.name is all quick)
is there a way i can optimise this?
to be fair, the 'entity' view already has the name of the device as another field (node), so i could use this instead but i would like the relation to exist.
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您是否尝试过 .select_lated() 在您看来？
另一方面，如果它是旧数据库，并且不是由django自动生成的，可能node_id可能不是数据库中的索引，这会减慢任何JOIN的速度。
have you try .select_related() in your view?
in the other hand, if it is and old database, and no autogenerated by django, probably node_id may not be an index in the database, this will slow down a lot any JOIN.