Powershell - Asignación de usuarios SQL Server 2012

Suponiendo que se crea su inicio de sesión

## Creating database user and assigning database role    

#get variables
$instanceName = "yourInstance"
$loginName = "testLogin"
$dbUserName = "testUserName"
$databasename = "tempdb"
$roleName = "db_backupoperator"
$server = New-Object -TypeName Microsoft.SqlServer.Management.Smo.Server -ArgumentList $instanceName

#add a database mapping
$database = $server.Databases[$databasename]
$login = $server.Logins[$loginName]
if ($database.Users[$dbUserName])
{
    $database.Users[$dbUserName].Drop()
}
$dbUser = New-Object `
-TypeName Microsoft.SqlServer.Management.Smo.User `
-ArgumentList $database, $dbUserName
$dbUser.Login = $loginName
$dbUser.Create()

#assign database role for a new user
$dbrole = $database.Roles[$roleName]
$dbrole.AddMember($dbUserName)
$dbrole.Alter