No sitecollections available in content database

After a content database restore we coudn't access our sitecollection anymore. We verifed the content database status and number of sitecollections. In our case, the current number of sitecollections was equal to 0.

We fixed this by running a couple of Powershell commands...

1. Retrieve content database GUID

Get-SPContentDatabase

2. Synchronizes the content database with the configuration database of the farm with respect to what site collections actually exist in the content database

$cdb = get-spcontentdatabase -Identity [insert guid of contentdatabase here]
$cdb.RefreshSitesInConfigurationDatabase()

Reference: MSDN