Question

我需要一种方法来选择外键的子集，但只能将其限制为子集。这是旧PHP数据库中使用的原始查询;

SELECT a.name FROM character_trait b
LEFT JOIN trait a ON b.id_trait = a.id
WHERE b.id_character = 1
AND a.id_traittype = 10

所有表格，字符，特征，特征类型和character_trait都可用，但我无法弄清楚如何在Djando中完成它。我的想法是这样的;

traits = CharacterTrait.objects.filter( id_character = character, id_trait.id_traittype = 10 )

但这只是一个错误＆＃34;关键字不能成为表达式＆＃34;。我可以用一种非常丑陋的方式做到这一点，并且只是迭代所产生的特征＆＃39;像这样使用for循环;

traits = CharacterTrait.objects.filter( id_character = character )  

for t in traits:
    print t.id_trait.id_traittype.id

    if t.id_trait.id_traittype.id == 10:
        print "Got One"

编辑，模块定义;

class Trait(models.Model):
    id = models.IntegerField(primary_key=True)  # AutoField? 
    id_traittype = models.ForeignKey(Traittype, null=True, db_column = 'id_traittype')

    name = models.CharField(max_length=32)

    class Meta:
        managed = False
        db_table = 'trait'

    def __unicode__(self):
                return self.name

class Traittype(models.Model):
    id = models.IntegerField(primary_key=True)  # AutoField?
    name = models.CharField(max_length=64)

    class Meta:
        managed = False
        db_table = 'traittype'

    def __unicode__(self):
                return self.name    

class Trait(models.Model):
    id = models.IntegerField(primary_key=True)  # AutoField? 
    id_traittype = models.ForeignKey(Traittype, null=True, db_column = 'id_traittype')

    name = models.CharField(max_length=32)

    class Meta:
        managed = False
        db_table = 'trait'

    def __unicode__(self):
                return self.name

class CharacterTrait(models.Model):
    id = models.IntegerField(primary_key=True)  # AutoField?
    ##id_character = models.IntegerField()
    ## id_trait = models.IntegerField()
    id_character = models.ForeignKey(Werewolfcharacter, null=True, db_column = 'id_character')
    id_trait     = models.ForeignKey(Trait,             null=True, db_column = 'id_trait')

    class Meta:
        managed = False
        db_table = 'character_trait'

    def __unicode__(self):
                return self.id_trait.name

Answer 1

一个简单的可能性，因为您（可能）已经在PHP代码中拥有正确的SQL，只需要use raw SQL queries in Django。

Answer 2

我打算建议你需要链接过滤器，比如

traits = CharacterTrait.objects.filter( id_character = character).filter(id_trait__id_traittype = 10 )

但回头看一些代码，

traits = CharacterTrait.objects.filter( id_character = character, id_trait__id_traittype = 10 )

应该足够了，关键是要取代它。使用__，如dm03514

所示

Answer 3

您应该阅读lookups that span relationships上的文档。您需要使用双下划线语法：

CharacterTrait.objects.filter(id_character=character, id_trait__id_traittype=10)

Django，外键的子集

3 个答案: