save software version in the database

The version represents the software version that was used to
import the data.

nominatim/db/properties.py

@@ -0,0 +1,28 @@
+"""
+Query and access functions for the in-database property table.
+"""
+
+def set_property(conn, name, value):
+    """ Add or replace the propery with the given name.
+    """
+    with conn.cursor() as cur:
+        cur.execute('SELECT value FROM nominatim_properties WHERE property = %s',
+                    (name, ))
+
+        if cur.rowcount == 0:
+            sql = 'INSERT INTO nominatim_properties (value, property) VALUES (%s, %s)'
+        else:
+            sql = 'UPDATE nominatim_properties SET value = %s WHERE property = %s'
+
+        cur.execute(sql, (value, name))
+    conn.commit()
+
+def get_property(conn, name):
+    """ Return the current value of the given propery or None if the property
+        is not set.
+    """
+    with conn.cursor() as cur:
+        cur.execute('SELECT value FROM nominatim_properties WHERE property = %s',
+                    (name, ))
+
+        return cur.fetchone()[0] if cur.rowcount > 0 else None