Basic connection class retargeting (#65)

- Allow modification of dbclass attribute
- Only allow updates to a valid (known) dbclass type.

That is, you can change the database type. 
Other attributes (like ssl and all the various auth modes are not yet supported)

Now you can take: mysql-test-db.yourcompany.com, and move it to postgres-prod-db.yourcompany.com and update the dbclass to match!

Author: t8y8

tableaudocumentapi/connection.py

@@ -3,6 +3,7 @@
 # Connection - A class for writing connections to Tableau files
 #
 ###############################################################################
+from tableaudocumentapi.dbclass import is_valid_dbclass
 
 
 class Connection(object):
@@ -111,3 +112,12 @@ def authentication(self):
     @property
     def dbclass(self):
         return self._class
+
+    @dbclass.setter
+    def dbclass(self, value):
+
+        if not is_valid_dbclass(value):
+            raise AttributeError("'{}' is not a valid database type".format(value))
+
+        self._class = value
+        self._connectionXML.set('dbclass', value)

tableaudocumentapi/dbclass.py

@@ -0,0 +1,60 @@
+
+
+KNOWN_DB_CLASSES = ('msaccess',
+                    'msolap',
+                    'bigquery',
+                    'asterncluster',
+                    'bigsql',
+                    'aurora',
+                    'awshadoophive',
+                    'dataengine',
+                    'DataStax',
+                    'db2',
+                    'essbase',
+                    'exasolution',
+                    'excel',
+                    'excel-direct',
+                    'excel-reader',
+                    'firebird',
+                    'powerpivot',
+                    'genericodbc',
+                    'google-analytics',
+                    'googlecloudsql',
+                    'google-sheets',
+                    'greenplum',
+                    'saphana',
+                    'hadoophive',
+                    'hortonworkshadoophive',
+                    'maprhadoophive',
+                    'marklogic',
+                    'memsql',
+                    'mysql',
+                    'netezza',
+                    'oracle',
+                    'paraccel',
+                    'postgres',
+                    'progressopenedge',
+                    'redshift',
+                    'snowflake',
+                    'spark',
+                    'splunk',
+                    'kognitio',
+                    'sqlserver',
+                    'salesforce',
+                    'sapbw',
+                    'sybasease',
+                    'sybaseiq',
+                    'tbio',
+                    'teradata',
+                    'vectorwise',
+                    'vertica',
+                    'denormalized-cube',
+                    'csv',
+                    'textscan',
+                    'webdata',
+                    'webdata-direct',
+                    'cubeextract')
+
+
+def is_valid_dbclass(dbclass):
+    return dbclass in KNOWN_DB_CLASSES

test/bvt.py

@@ -64,6 +64,13 @@ def test_can_write_attributes_to_connection(self):
         self.assertEqual(conn.username, 'bob')
         self.assertEqual(conn.server, 'mssql2014.test.tsi.lan')
 
+    def test_bad_dbclass_rasies_attribute_error(self):
+        conn = Connection(self.connection)
+        conn.dbclass = 'sqlserver'
+        self.assertEqual(conn.dbclass, 'sqlserver')
+        with self.assertRaises(AttributeError):
+            conn.dbclass = 'NotReal'
+
 
 class DatasourceModelTests(unittest.TestCase):