27.Django多数据库

Django多数据库联用

Django中每个app都可以单独设置一个数据库

settings.py中有数据库的相关设置,有一个默认的数据库 default,我们可以再加一些其它的

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
    },
    'db1': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'db_name1',
        'USER': 'your_user_name',
        'PASSWORD': 'your_password',
        "HOST": "localhost",
    },
    'db2': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'db_name2',
        'USER': 'your_user_name',
        'PASSWORD': 'your_password',
        "HOST": "localhost",
    },
}

# use multi-database in django
DATABASE_ROUTERS = ['project_name.database_router.DatabaseAppsRouter']
DATABASE_APPS_MAPPING = {
    # example:
    #'app_name':'database_name',
    'app1': 'db1',
    'app2': 'db2',
}

在project_name文件夹中存放 database_router.py 文件

# -*- coding: utf-8 -*-
from django.conf import settings

DATABASE_MAPPING = settings.DATABASE_APPS_MAPPING


class DatabaseAppsRouter(object):
    """
    A router to control all database operations on models for different
    databases.

    In case an app is not set in settings.DATABASE_APPS_MAPPING, the router
    will fallback to the `default` database.

    Settings example:

    DATABASE_APPS_MAPPING = {'app1': 'db1', 'app2': 'db2'}
    """

    def db_for_read(self, model, **hints):
        """"Point all read operations to the specific database."""
        if model._meta.app_label in DATABASE_MAPPING:
            return DATABASE_MAPPING[model._meta.app_label]
        return None

    def db_for_write(self, model, **hints):
        """Point all write operations to the specific database."""
        if model._meta.app_label in DATABASE_MAPPING:
            return DATABASE_MAPPING[model._meta.app_label]
        return None

    def allow_relation(self, obj1, obj2, **hints):
        """Allow any relation between apps that use the same database."""
        db_obj1 = DATABASE_MAPPING.get(obj1._meta.app_label)
        db_obj2 = DATABASE_MAPPING.get(obj2._meta.app_label)
        if db_obj1 and db_obj2:
            if db_obj1 == db_obj2:
                return True
            else:
                return False
        return None

    def allow_migrate(self, db, app_label, model_name=None, **hints):
        print db, app_label, model_name, hints
        if db in DATABASE_MAPPING.values():
            return DATABASE_MAPPING.get(app_label) == db
        elif app_label in DATABASE_MAPPING:
            return False
        return None

这样就启用了多数据,如果不设置或者没有设置的app就会自动使用默认的数据库

指定数据库来执行操作

# 查询
YourModel.objects.using('db1').all() 
或者 YourModel.objects.using('db2').all()

# 保存 或 删除
user_obj.save(using='new_users')
user_obj.delete(using='other_users')

多个数据库联用时数据导入导出 如果不是defalut(默认数据库)要在命令后边加 --database=数据库对应的settings.py中的名称
如: --database=db1 或 --database=db2

同步数据库

python manage.py migrate --database=db1

数据导出

python manage.py dumpdata app1 --database=db1 > app1_bak.json

数据库导入

python manage.py loaddata app1_bak.json --database=db1
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