文章目录

Django_database migrations 数据库迁移及其相关若干问题/迁移问题排查/迁移和sql语句预览

Django_database migrations 数据库迁移及其相关若干问题/迁移问题排查/迁移和sql语句预览

references

使用Django的个人习惯

常用主命令

django-admin and manage.py | Django documentation | Django (djangoproject.com)

$ django-admin <command> [options]
$ manage.py <command> [options]
$ python -m django <command> [options]

关于迁移的一些问题参考

How to simplify migrations in Django 1.7? - Stack Overflow
- 该问题涉及migaration 故障解决
I accidentally deleted the migrations folder in Django - Stack Overflow
Django deleted migrations directory - Stack Overflow
How to Back Up and Restore a MySQL Database {Easy Tutorial} (phoenixnap.com)

误删migrations文件夹后

migration django

sqlmigrate:检查migrations对应的sql操作

Specifies the database for which to generate the SQL. Defaults to default.

例如

python manage.py sqlmigrate polls 0001

(ll_env) PS D:\repos\IdeaProjects\djangoProjects\ela_old\ela> py manage.py sqlmigrate word 0001
--
-- Create model Word
--
--
-- Create model WordNotes
--
--
-- Create model Cet4WordsReq
--
CREATE TABLE `cet4_words_req` (`wordOrder` integer AUTO_INCREMENT NOT NULL PRIMARY KEY, `spelling` varchar(255) NOT NULL);
--
-- Create model Cet6WordsReq
--

migrations 中的迁移文件

migrations.CreateModel(
            name='Word',
            fields=[
                ('wid', models.AutoField(primary_key=True, serialize=False)),
                ('spelling', models.CharField(max_length=255)),
                ('phonetic', models.CharField(blank=True, max_length=255, null=True)),
                ('plurality', models.CharField(blank=True, max_length=255, null=True)),
                ('thirdpp', models.CharField(blank=True, max_length=255, null=True)),
                ('present_participle', models.CharField(blank=True, max_length=255, null=True)),
                ('past_tense', models.CharField(blank=True, max_length=255, null=True)),
                ('past_participle', models.CharField(blank=True, max_length=255, null=True)),
                ('explains', models.TextField(blank=True, null=True)),
            ],
            options={
                'db_table': 'words',
                'managed': False,
            },
        ),
        migrations.CreateModel(
            name='WordNotes',
            fields=[
                ('id', models.BigAutoField(primary_key=True, serialize=False)),
                ('wordspelling', models.CharField(blank=True, db_column='wordSpelling', max_length=255, null=True)),
                ('uid', models.IntegerField(blank=True, db_column='UID', null=True)),
                ('content', models.CharField(blank=True, max_length=255, null=True)),
                ('difficulty_rate', models.IntegerField(blank=True, null=True)),
            ],
            options={
                'db_table': 'word_notes',
                'managed': False,
            },
        ),

出现sql语句为空的create操作正是由于option中managed取值所造成的
但是建议您从Model中修改,然后重新makemigrations

可以配合下方的showmigrations命令中的列表来查看指定某个变迁所对应的sql语句映射

一般的,initial文件中记录的是初次依照app中的各个模型来创建对应的数据库表的create语句

showmigrations, which lists a project’s migrations and their status.

以app 为单位进行显示

cxxu➜~/djangoProjects/ela(main✗)» pmg showmigrations                                                                                                                       [18:57:33]
admin
 [X] 0001_initial
 [X] 0002_logentry_remove_auto_add
 [X] 0003_logentry_add_action_flag_choices
auth
 [X] 0001_initial
 [X] 0002_alter_permission_name_max_length
contenttypes
 [X] 0001_initial
 [X] 0002_remove_content_type_name
scoreImprover
 [X] 0001_initial
sessions
 [X] 0001_initial
user
 [X] 0001_initial
 [X] 0002_remove_user_test_alter_user_examdate_and_more
 [X] 0003_alter_user_examdate_alter_user_examtype
words
 [X] 0001_initial

models.py文件

manage.py makemigrations

该命令可以检查django app的models.py 文件中是否发生变更,并生成对应的数据库变迁操作,来同步数据库;
- 这些检查出来的变化所对应的模型操作会记录在文件中,存放在app的migrations目录下
在执行该命令的时候,应当加上具体的app 名称,以保证makemigrations 过程能够正确执行

manage.py migrate

该操作可以执行makemigrations产生的文件,从而同步模型和数据库(表)结构

从已有的mysql数据库迁移到django项目中(django import exsited databases from mysql)

reference1

Adding migrations to apps¶

You have not changed your modelssince you made theirtables. For migrations to work, you must make the initial migration *first*and then make changes, as Django compares changes against migration files, not the database.
You have not manually edited your database - Django won’t be able to detect that your database doesn’t match your models, you’ll just get errors when migrations try to modify those tables.

确保initial(–fake-initial)

reference2

How to Connect Django to an Existing Legacy Database | DevRa (rafed.github.io)
- Get an existing database
- Import the data to MySQL
- Setup Django project to work with MySQL
- Create the Django models from MySQL
- Create app and use the models
- Modifying database tables

Create the Django models from MySQL

The above below will produce django models in models.py from tables present in MySQL.

$ python manage.py inspectdb > models.py

Modifying database tables

Legacy tables are not permitted to be modified by default.
- But they can be modified if needed.
First set managed=True in sub Meta classes of classes you want to modify.
And then, add the new field you want.

    class Meta:
        managed = True
        db_table = 'customers'

Now, make the migrations file.

 python manage.py makemigrations

 python manage.py migrate --fake

Voila! Now the new table field should be added!