Django 多數據庫支持

不少時候,須要去其餘數據庫查詢數據,都將會面臨多數據庫支持問題.

1.在settings文件內添加多數據庫鏈接

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', } }

若是默認數據庫的概念在項目上下文中沒有意義，則須要始終當心地指定要使用的數據庫。Django須要一個default數據庫,若是不須要使用,能夠設置爲空字典.

舉個栗子

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

若是你試圖鏈接一個沒有在DATABASES內定義的數據庫django將產生django.db.utils.ConnectionDoesNotExist異常

將模型同步到數據庫

./manage.py migrate  # 操做將同步到default數據庫
./manage.py migrate --database=test  # 同步到test數據庫

若是不是想全部的模型都同步到一個數據庫上你能夠定義一個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文件內添加DATABASE_ROUTERS參數

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

爲測試model指定,在test01的models文件內寫入

from django.db import models import shortuuid # Create your models here.


def createuuid(): return shortuuid.uuid() class CourseManage(models.Model): """課程管控表""" uuid = models.CharField( 'ID', max_length=22, primary_key=True, default=createuuid, editable=False) add_time = models.DateTimeField('建立時間', auto_now_add=True) del_state_type = ((0, '已刪除'), (1, '默認')) modified_time = models.DateTimeField('修改時間', auto_now=True) del_state = models.IntegerField( '刪除狀態', choices=del_state_type, default=1, db_index=True) config_status = ((1, '進行中'), (2, '完結'), ) remote_id = models.CharField(verbose_name='遠端產品id', max_length=30) status = models.PositiveSmallIntegerField(choices=config_status, default=1) class Meta: verbose_name = '課程' verbose_name_plural = verbose_name db_table = 'backend_coursemanage'

db_table指定此模型在遠端的數據庫內的表名稱.否則會報錯

按照上述操做,便能鏈接並查詢.

 

標籤:當項目須要執行python manage.py makemigrations時,會發現,test01項目的migrations文件夾會產生migrations文件.而且終端也會產生提示,

能夠嘗試刪除此migrations,來避免這個問題,allow_migrate的判斷只針對真正的migrate操做.

 

如何選擇數據庫? 

1.模型層

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

2.原生光標

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

 

關於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'])  # 這裏是重點

    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