python – 联合和相交在Django

class Tag(models.Model):
  name = models.CharField(maxlength=100)

class Blog(models.Model):
  name = models.CharField(maxlength=100)
  tags =  models.ManyToManyField(Tag)

简单的模型只是问我的问题。

我不知道如何我用两种不同的方式使用标签查询博客。

>标有“tag1”或“tag2”的博客条目:
Blog.objects.filter(tags_in = [1,2])。distinct()
>标记有“tag1”和“tag2”的博客对象:?
>用“tag1”和“tag2”标记的博客对象,没有别的东西。

标签和博客只是用于一个例子。

你可以使用Q对象#1:

# Blogs who have either hockey or django tags.
from django.db.models import Q
Blog.objects.filter(
    Q(tags__name__iexact='hockey') | Q(tags__name__iexact='django')
)

我相信,联合和交叉点有点超出了Django ORM的范围,但它可能对这些。以下示例来自称为django-tagging的Django应用程序,它提供了该功能。 Line 346 of models.py

对于第二部分,你基本上寻找两个查询的联合

def get_union_by_model(self, queryset_or_model, tags):
    """
    Create a ``QuerySet`` containing instances of the specified
    model associated with *any* of the given list of tags.
    """
    tags = get_tag_list(tags)
    tag_count = len(tags)
    queryset, model = get_queryset_and_model(queryset_or_model)

    if not tag_count:
        return model._default_manager.none()

    model_table = qn(model._meta.db_table)
    # This query selects the ids of all objects which have any of
    # the given tags.
    query = """
    SELECT %(model_pk)s
    FROM %(model)s, %(tagged_item)s
    WHERE %(tagged_item)s.content_type_id = %(content_type_id)s
      AND %(tagged_item)s.tag_id IN (%(tag_id_placeholders)s)
      AND %(model_pk)s = %(tagged_item)s.object_id
    GROUP BY %(model_pk)s""" % {
        'model_pk': '%s.%s' % (model_table, qn(model._meta.pk.column)),
        'model': model_table,
        'tagged_item': qn(self.model._meta.db_table),
        'content_type_id': ContentType.objects.get_for_model(model).pk,
        'tag_id_placeholders': ','.join(['%s'] * tag_count),
    }

    cursor = connection.cursor()
    cursor.execute(query, [tag.pk for tag in tags])
    object_ids = [row[0] for row in cursor.fetchall()]
    if len(object_ids) > 0:
        return queryset.filter(pk__in=object_ids)
    else:
        return model._default_manager.none()

对于第3部分,我相信你正在寻找一个交叉点。见line 307 of models.py

def get_intersection_by_model(self, queryset_or_model, tags):
    """
    Create a ``QuerySet`` containing instances of the specified
    model associated with *all* of the given list of tags.
    """
    tags = get_tag_list(tags)
    tag_count = len(tags)
    queryset, model = get_queryset_and_model(queryset_or_model)

    if not tag_count:
        return model._default_manager.none()

    model_table = qn(model._meta.db_table)
    # This query selects the ids of all objects which have all the
    # given tags.
    query = """
    SELECT %(model_pk)s
    FROM %(model)s, %(tagged_item)s
    WHERE %(tagged_item)s.content_type_id = %(content_type_id)s
      AND %(tagged_item)s.tag_id IN (%(tag_id_placeholders)s)
      AND %(model_pk)s = %(tagged_item)s.object_id
    GROUP BY %(model_pk)s
    HAVING COUNT(%(model_pk)s) = %(tag_count)s""" % {
        'model_pk': '%s.%s' % (model_table, qn(model._meta.pk.column)),
        'model': model_table,
        'tagged_item': qn(self.model._meta.db_table),
        'content_type_id': ContentType.objects.get_for_model(model).pk,
        'tag_id_placeholders': ','.join(['%s'] * tag_count),
        'tag_count': tag_count,
    }

    cursor = connection.cursor()
    cursor.execute(query, [tag.pk for tag in tags])
    object_ids = [row[0] for row in cursor.fetchall()]
    if len(object_ids) > 0:
        return queryset.filter(pk__in=object_ids)
    else:
        return model._default_manager.none()
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