Django：unique_together暗示db_index = True与ForeignKey一样吗？

A field on a model, foo = models.ForeignKey(Foo) will automatically add a database index for the column, in order to make look-ups faster. That's good and well, but Django's docs don't state whether the fields in a model-meta's unique_together receive the same treatment. I happen to have a model in which one char field which is listed in unique_together requires an index for quick lookups. I know that it won't hurt anything to add a duplicate db_index=True in the field definition, but I'm curious.

模型上的字段foo = models.ForeignKey（Foo）将自动为列添加数据库索引，以便更快地查找。这很好，但Django的文档没有说明模型元的unique_together中的字段是否接受相同的处理。我碰巧有一个模型，其中unique_together中列出的一个char字段需要一个快速查找索引。我知道在字段定义中添加重复的db_index = True不会有任何损害，但我很好奇。

4 个解决方案

#1

If unique_together does add an index, it will be a multiple column index.

如果unique_together确实添加了索引，那么它将是一个多列索引。

If you want one of the columns to be indexed individually, I believe you need to specify db_index=True in the field definition.

如果您希望单独索引其中一列，我相信您需要在字段定义中指定db_index = True。

#2

For anyone coming here wondering if they need an index_together in addition to unique_together to get the index's performance benefit, the answer for Postgres is no, they are functionally the same.

对于任何来到这里的人，想知道除了unique_together还需要index_together以获得索引的性能优势，Postgres的答案是否定的，它们在功能上是相同的。

#3

In Django 1.5 and higher, you can use the {Model}.Meta.index_together class attribute. If you had two fields named foo and bar, you would add:

在Django 1.5及更高版本中，您可以使用{Model} .Meta.index_together类属性。如果你有两个名为foo和bar的字段，你会添加：

class Meta(object):
    index_together = unique_together = [
        ['foo', 'bar']
    ]

If you have only one set of unique fields, you can use a one-dimensional iterable for unique_together. However, the documentation does not indicate that the same applies to index_together.

如果您只有一组唯一字段，则可以对unique_together使用一维可迭代。但是，文档并未指出同样适用于index_together。

This would also be okay:

这也没关系：

class Meta(object):
    unique_together = 'foo', 'bar'
    index_together = [
        ['foo', 'bar']
    ]

This, however, is NOT supported by the documentation:

但是，文档不支持此操作：

class Meta(object):
    unique_together = 'foo', 'bar'
    index_together = 'foo', 'bar'

#4

According to the docs, it will only enforce uniqueness on database level. I think generally making a field unique does not imply it has an index. Though you could also simply check on db level if the index exists. Everything indicates though it does not.

根据文档，它只会强制数据库级别的唯一性。我认为通常使字段唯一并不意味着它有一个索引。虽然如果索引存在，您也可以简单地检查数据库级别。一切都表明虽然没有。

#1