django-batch-select 0.2.4

示例用法

假设我们有如下定义的模型：

from batch_select.models import BatchManager

class Tag(models.Model):
    name = models.CharField(max_length=32)

class Section(models.Model):
    name = models.CharField(max_length=32)

    objects = BatchManager()

class Entry(models.Model):
    title = models.CharField(max_length=255)
    section = models.ForeignKey(Section, blank=True, null=True)
    tags = models.ManyToManyField(Tag)

    objects = BatchManager()

我还将定义一个helper函数来显示生成的sql查询：

from django import db

def show_queries():
    for query in db.connection.queries:
        print query["sql"]
    db.reset_queries()

下面是几个示例（使用生成的sql查询）：

>>> Entry.objects.batch_select('tags').all()
[]
>>> show_queries() # no results, so no 2nd query
SELECT "batch_select_entry"."id", "batch_select_entry"."title", "batch_select_entry"."section_id" FROM "batch_select_entry"
>>> Entry.objects.create()
>>> Entry.objects.create()
>>> tag1 = Tag.objects.create(name='tag1')
>>> tag2 = Tag.objects.create(name='tag2')
>>> db.reset_queries()
>>> entries = Entry.objects.batch_select('tags').all()
>>> entry = entries[0]
>>> print entry.tags_all
[]
>>> show_queries()
SELECT "batch_select_entry"."id", "batch_select_entry"."title", "batch_select_entry"."section_id" FROM "batch_select_entry" LIMIT 1
SELECT (`batch_select_entry_tags`.`entry_id`) AS "entry_id", "batch_select_tag"."id", "batch_select_tag"."name" FROM "batch_select_tag" INNER JOIN "batch_select_entry_tags" ON ("batch_select_tag"."id" = "batch_select_entry_tags"."tag_id") WHERE "batch_select_entry_tags".entry_id IN (1)
>>> entry.tags.add(tag1)
>>> db.reset_queries()
>>> entries = Entry.objects.batch_select('tags').all()
>>> entry = entries[0]
>>> print entry.tags_all
[<Tag: Tag object>]
>>> show_queries()
SELECT "batch_select_entry"."id", "batch_select_entry"."title", "batch_select_entry"."section_id" FROM "batch_select_entry" LIMIT 1
SELECT (`batch_select_entry_tags`.`entry_id`) AS "entry_id", "batch_select_tag"."id", "batch_select_tag"."name" FROM "batch_select_tag" INNER JOIN "batch_select_entry_tags" ON ("batch_select_tag"."id" = "batch_select_entry_tags"."tag_id") WHERE "batch_select_entry_tags".entry_id IN (1)
>>> entries = Entry.objects.batch_select('tags').all()
>>> for entry in entries:
....     print entry.tags_all
....
[<Tag: Tag object>]
[]
>>> show_queries()
SELECT "batch_select_entry"."id", "batch_select_entry"."title", "batch_select_entry"."section_id" FROM "batch_select_entry"
SELECT (`batch_select_entry_tags`.`entry_id`) AS "entry_id", "batch_select_tag"."id", "batch_select_tag"."name" FROM "batch_select_tag" INNER JOIN "batch_select_entry_tags" ON ("batch_select_tag"."id" = "batch_select_entry_tags"."tag_id") WHERE "batch_select_entry_tags".entry_id IN (1, 2)

在不使用批处理选择的情况下重新运行相同的last for循环 生成三个查询而不是两个（n+1查询）：

>>> entries = Entry.objects.all()
>>> for entry in entries:
....     print entry.tags.all()
....
[<Tag: Tag object>]
[]

>>> show_queries()
SELECT "batch_select_entry"."id", "batch_select_entry"."title", "batch_select_entry"."section_id" FROM "batch_select_entry"
SELECT "batch_select_tag"."id", "batch_select_tag"."name" FROM "batch_select_tag" INNER JOIN "batch_select_entry_tags" ON ("batch_select_tag"."id" = "batch_select_entry_tags"."tag_id") WHERE "batch_select_entry_tags"."entry_id" = 1
SELECT "batch_select_tag"."id", "batch_select_tag"."name" FROM "batch_select_tag" INNER JOIN "batch_select_entry_tags" ON ("batch_select_tag"."id" = "batch_select_entry_tags"."tag_id") WHERE "batch_select_entry_tags"."entry_id" = 2

这也适用于反向外键。例如，我们可以 属于每个部分的条目：

>>> section1 = Section.objects.create(name='section1')
>>> section2 = Section.objects.create(name='section2')
>>> Entry.objects.create(section=section1)
>>> Entry.objects.create(section=section1)
>>> Entry.objects.create(section=section2)
>>> db.reset_queries()
>>> Section.objects.batch_select('entry_set')
[<Section: Section object>, <Section: Section object>]
>>> show_queries()
SELECT "batch_select_section"."id", "batch_select_section"."name" FROM "batch_select_section" LIMIT 21
SELECT ("batch_select_entry"."section_id") AS "__section_id", "batch_select_entry"."id", "batch_select_entry"."title", "batch_select_entry"."section_id", "batch_select_entry"."location_id" FROM "batch_select_entry" WHERE "batch_select_entry"."section_id" IN (1, 2)

查询中的每个section对象都有一个entry\u set\u all字段 包含相关条目的。

您需要通过批选择外键的“相关名称”， 在本例中为“条目集”。nb默认情况下，外文的相关名称 键实际上不包含_set后缀，因此您可以仅使用“entry” 在这种情况下。我已经确定了后缀集版本也适用于 尽量让api更简单。

更高级的用法

默认情况下，批处理字段插入到名为<name>_all的字段中， 在每个物体上。所以：

Entry.objects.batch_select('tags').all()

结果在条目实例中包含名为^{tt2}的字段$ 包含与该条目关联的标记对象。

如果您想给字段起一个不同的名称，只需使用关键字 参数-与使用Aggregationapi相同：

Entry.objects.batch_select(selected_tags='tags').all()

将意味着标记对象将被分配到名为 'selected_tags'。

如果要对相关对象执行筛选，则需要 使用批处理对象。通过这样做，您可以传递额外的关键字参数 与使用queryset的filter方法相同：

from batch_select.models import Batch

Entry.objects.batch_select(tags_containing_blue=Batch('tags', name__contains='blue'))

将返回名为“tags\u containing\u name”的字段的条目对象 只有那些名字中含有“蓝色”的标签。

除了使用关键字参数进行筛选之外，还可以调用 对批处理对象执行以下方法，并传递其效果 到底层QuerySet对象：

• filter
• exclude
• annotate
• order_by
• reverse
• select_related
• extra
• defer
• only
• 批量选择

（注意，distinct（）、values（）等不包括在内 附加查询如何与原始查询关联的副作用） 例如，为了达到与上面的过滤器相同的效果 执行以下操作：

from batch_select.models import Batch

Entry.objects.batch_select(tags_containing_blue=Batch('tags').filter(name__contains='blue'))

但是，以下内容将排除包含“蓝色”和按名称排序的标记：

from batch_select.models import Batch

batch = Batch('tags').exclude(name__contains='blue').order_by('name')
Entry.objects.batch_select(tags_not_containing_blue=batch)

兼容性

Django批量选择至少应与Django 1.1-1.3一起使用。

TODOS和错误

见：http://github.com/lilspikey/django-batch-select/issues