title: Django could not detect newly added database after adding router
body: <p>I have three database out of which one is set to default.</p>
  <p>I have already created router for ringi database and it working perfectly fine. Now i would like to add one more database and after creating the new router for database named cms, its not working.</p>
  <p>So my project name is wshp and one of router for ringi database, i placed it in same folder as settings.py.
  I created another app called mypage and created router for cms and name of router is cmsrouter.</p>
  <p>settings.py</p>
  <pre><code>DATABASE_ROUTERS = ['wshp.router.myrouter','app_mypage.cms_router.cmsrouter']
  
  DATABASE_APPS_MAPPING = {
      'ringi':'ringi_db',
      'cms':'cms_db'
  }
  
  DATABASES = {
      'default': {
          'ENGINE': 'django.db.backends.mysql',
          'NAME': 'mypage',
          'USER': 'root',
          'PASSWORD': '',
          'HOST': 'localhost',
          'PORT': '3306',
      },
      'ringi_db':{
          'ENGINE': 'django.db.backends.mysql',
          'NAME': 'ringi',
          'USER': 'root',
          'PASSWORD': '',
          'HOST': 'localhost',
          'PORT': '3306',
      },
      'cms_db':{
          'ENGINE': 'django.db.backends.mysql',
          'NAME': 'cms',
          'USER': 'root',
          'PASSWORD': '',
          'HOST': 'localhost',
          'PORT': '3306',
      }
  }
  </code></pre>
  <p>cms_router.py</p>
  <pre><code>class cmsrouter:
      def db_for_read(self, model, **hints):
          if model._meta.app_label == 'cms':
              return 'cms_db'
          else:
              return None
  
      def db_for_write(self, model, **hints):
          if model._meta.app_label == 'cms':
              return 'cms_db'
          else:
              return None
  
      def allow_relation(self, obj1, obj2, **hints):
          if obj1._meta.app_label == 'cms' or \
             obj2._meta.app_label == 'cms':
             return True
          else:
              return None
  
      def allow_migrate(self, db, app_label, model_name=None, **hints):
          if app_label == 'cms':
              return db == 'cms_db'
          else:
              return None
  
  </code></pre>
  <p>I added models for cms database and After running migrations for mypage app, I found No changes detected.
  If I add models for any other database then It gets detected but not for cms.</p>
  <p>I can not find any thing wrong in the router. Please help.</p>