如何在Django(1.8)迁移中删除索引varchar_pattern_ops? [英] How to remove index varchar_pattern_ops in a django (1.8) migration?

问题描述

使用 models.varchar(...)字段创建模型时，将创建 varchar_pattern_ops 索引.

When creating a model with a models.varchar(...) field, a varchar_pattern_ops index is being created.

这是在postgresql中生成的表

This is the table generated in postgresql

              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)

我想在迁移中删除该 varchar_pattern_ops 索引，并在该字段中添加一个哈希索引.

I want to remove that varchar_pattern_ops index in a migration, and add a hash index in that field.

我尝试这样做:

# models.py
class Btilog(models.Model):
    md5hash = models.TextField(db_index=False)
    [...]

在迁移过程中，还强制添加 db_field = False

And in migration also force adding 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

After running the migrations, this are the indexes in the database

                              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.django会自动添加此索引，请参见此

Note that public.logger_btilog_md5hash_6454d7bb20588b61_like is the index I want to delete. This index is being added automatically by django, see this

有关该索引的更多信息

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:我对哈希索引的使用并不感到困惑，我只想做 = (严格相等) where 在 md5hash 字段，那么(通常) hash 索引将是最快的，并且将比 btree 索引(django的默认值)

Footnote: I'm not confused about the usage of a hash index, I only want to do = (strictrly equal) where searches in md5hash field, then (casually) a hash index would be the fastest and will occupy less space than a btree index (django's default)

推荐答案

回答更新通知:

• django<1.11:使用此答案

• django < 1.11: Use this answer

django> = 1.11:使用@Cesar Canassa的答案

django >= 1.11: Use @Cesar Canassa's answer

好的，我在这里找到了一些信息

Ok, I found some info here https://docs.djangoproject.com/en/1.8/_modules/django/db/backends/base/schema/#BaseDatabaseSchemaEditor.alter_field

并进行了手动 RunPython 迁移，以使用 SchemaEditor

And made a manual RunPython migration to delete the varchar_pattern_ops index using the SchemaEditor

# -*- 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
        ),
    ]

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