Fix issues with column placeholders

lib/nexrad/db.py

@@ -91,23 +91,42 @@ class Database():
 
         return Database(db)
 
+    def column_placeholders(self, table, obj) -> list:
+        ctors = getattr(table, '__constructors__')
+
+        if ctors is None:
+            return ['?' for c in table.__columns__ if c != table.__key__]
+        if ctors is not None:
+            ret = list()
+
+            for c in table.__columns__:
+                if c == table.__key__:
+                    continue
+
+                if c in ctors:
+                    ret.append(ctors[c](getattr(obj, c)))
+                else:
+                    ret.append('?')
+
+            return ret
+
     def add(self, obj):
         table = type(obj)
         sql   = f"insert into {table.__table__} ("
         sql += ", ".join([c for c in table.__columns__ if c != table.__key__])
         sql += ') values ('
-        sql += ", ".join(['?' for c in table.__columns__ if c != table.__key__])
+        sql += ", ".join(self.column_placeholders(table, obj))
         sql += f") returning {table.__key__}"
 
         fn = getattr(obj, '__values__', None)
 
         if fn is not None:
-            values = fn()
+            values = fn(obj)
         else:
             values = list()
 
             for column in table.__columns__:
-                if column != table.__key__:
+                if column not in table.__constructors__ and column != table.__key__:
                     values.append(getattr(obj, column, None))
 
         cr = self.db.execute(sql, values)