Django 多数据库支持

很多时候,需要去其他数据库查询数据,都将会面临多数据库支持问题.

1.在settings文件内添加多数据库连接

DATABASES = {
    \'default\': {
        \'ENGINE\': \'django.db.backends.sqlite3\',
        \'NAME\': os.path.join(BASE_DIR, \'db.sqlite3\'),
    },
    \'test\': {
        \'ENGINE\': \'django.db.backends.mysql\',
        \'NAME\': \'pro_control\',
        \'USER\': \'root\',
        \'PASSWORD\': \'root\',
        \'HOST\': \'10.0.11.11\',
        \'PORT\': \'3306\',
    }
}

如果默认数据库的概念在项目上下文中没有意义，则需要始终小心地指定要使用的数据库。Django需要一个default数据库,如果不需要使用,可以设置为空字典.

举个栗子

DATABASES = {
    \'default\': {},
    \'users\': {
        \'NAME\': \'user_data\',
        \'ENGINE\': \'django.db.backends.mysql\',
        \'USER\': \'mysql_user\',
        \'PASSWORD\': \'superS3cret\'
    },
    \'customers\': {
        \'NAME\': \'customer_data\',
        \'ENGINE\': \'django.db.backends.mysql\',
        \'USER\': \'mysql_cust\',
        \'PASSWORD\': \'veryPriv@ate\'
    }
}

用例

如果你试图连接一个没有在DATABASES内定义的数据库django将产生django.db.utils.ConnectionDoesNotExist异常

将模型同步到数据库

./manage.py migrate  # 操作将同步到default数据库
./manage.py migrate --database=test  # 同步到test数据库

如果不是想所有的模型都同步到一个数据库上你可以定义一个database router,新建db_router.py文件

class AuthRouter:
    def db_for_read(self, model, **hits):
        if model._meta.app_label == \'test01\':
            return \'test\'
        return None

    def db_for_write(self, model, **hits):
        if model._meta.app_label == \'test01\':
            return \'test\'
        return None

    def allow_relation(self, obj1, obj2, **hits):
        if obj1._meta.app_label == \'test01\' or obj2._meta.app_label == \'test01\':
            return True
        return None

    def allow_migrate(self, db, app_label, model_name=None, **hits):
        if app_label == \'test01\':
            return db == \'test\'
        return None

在setting文件内添加DATABASE_ROUTERS参数

DATABASE_ROUTERS = [\'test01.db_router.AuthRouter\', ]

为测试model指定,在test01的models文件内写入

from django.db import models
import shortuuid

# Create your models here.


def createuuid():
    return shortuuid.uuid()


class CourseManage(models.Model):
    """课程管控表"""
    uuid = models.CharField(
        \'ID\',
        max_length=22,
        primary_key=True,
        default=createuuid,
        editable=False)
    add_time = models.DateTimeField(\'创建时间\', auto_now_add=True)

    del_state_type = ((0, \'已删除\'), (1, \'默认\'))
    modified_time = models.DateTimeField(\'修改时间\', auto_now=True)
    del_state = models.IntegerField(
        \'删除状态\', choices=del_state_type, default=1, db_index=True)
    config_status = ((1, \'进行中\'), (2, \'完结\'), )
    remote_id = models.CharField(verbose_name=\'远端产品id\', max_length=30)
    status = models.PositiveSmallIntegerField(choices=config_status, default=1)

    class Meta:
        verbose_name = \'课程\'
        verbose_name_plural = verbose_name
        db_table = \'backend_coursemanage\'

db_table指定此模型在远端的数据库内的表名称.不然会报错

按照上述操作,便能连接并查询.

 

标签:当项目需要执行python manage.py makemigrations时,会发现,test01项目的migrations文件夹会产生migrations文件.并且终端也会产生提示,

可以尝试删除此migrations,来避免这个问题,allow_migrate的判断只针对真正的migrate操作.

 

如何选择数据库? 

1.模型层

User.objects.using(\'legacy_users\').get(username=\'fred\')
user_obj.save(using=\'new_users\')
user_obj.delete(using=\'legacy_users\')

2.原生光标

from django.db import connections
with connections[\'my_db_alias\'].cursor() as cursor:
    ...

 

关于replication

DATABASES = {
    \'default\': {},
    \'auth_db\': {
        \'NAME\': \'auth_db\',
        \'ENGINE\': \'django.db.backends.mysql\',
        \'USER\': \'mysql_user\',
        \'PASSWORD\': \'swordfish\',
    },
    \'primary\': {
        \'NAME\': \'primary\',
        \'ENGINE\': \'django.db.backends.mysql\',
        \'USER\': \'mysql_user\',
        \'PASSWORD\': \'spam\',
    },
    \'replica1\': {
        \'NAME\': \'replica1\',
        \'ENGINE\': \'django.db.backends.mysql\',
        \'USER\': \'mysql_user\',
        \'PASSWORD\': \'eggs\',
    },
    \'replica2\': {
        \'NAME\': \'replica2\',
        \'ENGINE\': \'django.db.backends.mysql\',
        \'USER\': \'mysql_user\',
        \'PASSWORD\': \'bacon\',
    },
}

import random

class PrimaryReplicaRouter:
    def db_for_read(self, model, **hints):
        """
        Reads go to a randomly-chosen replica.
        """
        return random.choice([\'replica1\', \'replica2\'])  # 这里是重点

    def db_for_write(self, model, **hints):
        """
        Writes always go to primary.
        """
        return \'primary\'

    def allow_relation(self, obj1, obj2, **hints):
        """
        Relations between objects are allowed if both objects are
        in the primary/replica pool.
        """
        db_list = (\'primary\', \'replica1\', \'replica2\')
        if obj1._state.db in db_list and obj2._state.db in db_list:
            return True
        return None

    def allow_migrate(self, db, app_label, model_name=None, **hints):
        """
        All non-auth models end up in this pool.
        """
        return True