使用 models.varchar(...)
字段创建模型时,会创建一个 varchar_pattern_ops
索引。
这是在postgresql中生成的表
Table "public.logger_btilog"
Column | Type | Modifiers
------------------+--------------------------+-----------
md5hash | text |
id | integer | not null
Indexes:
"logger_btilog_pkey" PRIMARY KEY, btree (id)
"logger_btilog_md5hash_6454d7bb20588b61_like" btree (md5hash varchar_pattern_ops)
我想删除迁移中的 varchar_pattern_ops
索引,并在该字段中添加哈希索引。
我试过这样做:
# models.py
class Btilog(models.Model):
md5hash = models.TextField(db_index=False)
[...]
并且在迁移中还强制添加db_field=False
# 0013_migration.py
# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import models, migrations
class Migration(migrations.Migration):
dependencies = [
('logger', '0014_btilog_id'),
]
operations = [
# this should remove all indexes for md5hash, but it does not work
migrations.AlterField(
model_name='btilog',
name='md5hash',
field=models.TextField(null=True, blank=True, db_index=False),
),
migrations.RunSQL(
"create index logger_btilog_md5hash_hashindex on logger_btilog using hash(md5hash);",
"drop index logger_btilog_md5hash_hashindex;"
),
]
运行迁移后,这是数据库中的索引
relation | size
--------------------------------------------------------------------+---------
public.logger_btilog | 7185 MB
public.logger_btilog_md5hash_6454d7bb20588b61_like | 1442 MB
public.logger_btilog_md5hash_hashindex | 1024 MB
public.logger_btilog_pkey | 548 MB
请注意,public.logger_btilog_md5hash_6454d7bb20588b61_like
是我要删除的索引。此索引由 django 自动添加,请参阅 this
关于该指数的更多信息
vtfx=# \d logger_btilog_md5hash_6454d7bb20588b61_like
Index "public.logger_btilog_md5hash_6454d7bb20588b61_like"
Column | Type | Definition
---------+------+------------
md5hash | text | md5hash
btree, for table "public.logger_btilog"
脚注:我对哈希索引的用法并不感到困惑,我只想做 =
(严格等于) where
在 md5hash< 中搜索
字段,然后(随便)一个 hash
索引将是最快的,并且比 btree
索引(django 的默认)占用更少的空间
最佳答案
Answer update notice:
django < 1.11: Use this answer
django >= 1.11: Use @Cesar Canassa's answer
好的,我在这里找到了一些信息 https://docs.djangoproject.com/en/1.8/_modules/django/db/backends/base/schema/#BaseDatabaseSchemaEditor.alter_field
并使用 SchemaEditor
进行手动 RunPython
迁移以删除 varchar_pattern_ops
索引
# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import models, migrations
import re
def drop_md5hash_varchar_pattern_ops_index(apps, schemaEditor):
# code based on https://docs.djangoproject.com/en/1.8/_modules/django/db/backends/base/schema/#BaseDatabaseSchemaEditor.alter_field
model = apps.get_model("logger", "Btilog")
index_names = schemaEditor._constraint_names(model, index=True)
for index_name in index_names:
if re.search('logger_btilog_md5hash_.+_like', index_name):
print 'dropping index {}'.format(index_name)
schemaEditor.execute(schemaEditor._delete_constraint_sql(schemaEditor.sql_delete_index, model, index_name))
class Migration(migrations.Migration):
dependencies = [
('logger', '0012_auto_20150529_1745'),
]
operations = [
# Remove the annoying index using a hack
migrations.RunPython(
drop_md5hash_varchar_pattern_ops_index
),
]
关于django - 如何在 django (1.8) 迁移中删除索引 varchar_pattern_ops?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/32773049/