Add Type.to_sql() and simplify model code

Instead of encoding the conversion behaviour in the model class (via
the `_bytes_keys` attribute) we define it on the type. This gives us
a more extensible interface and separates logic.

This should not change any behaviour (as one can see by closely staring
at the code).

beets/dbcore/db.py

@@ -115,11 +115,6 @@ class Model(object):
     keys are field names and the values are `Type` objects.
     """
 
-    _bytes_keys = ()
-    """Keys whose values should be stored as raw bytes blobs rather than
-    strings.
-    """
-
     _search_fields = ()
     """The fields that should be queried by default by unqualified query
     terms.
@@ -338,11 +333,7 @@ class Model(object):
             if key != 'id' and key in self._dirty:
                 self._dirty.remove(key)
                 assignments += key + '=?,'
-                value = self[key]
-                # Wrap path strings in buffers so they get stored
-                # "in the raw".
-                if key in self._bytes_keys and isinstance(value, str):
-                    value = buffer(value)
+                value = self._type(key).to_sql(self[key])
                 subvars.append(value)
         assignments = assignments[:-1]  # Knock off last ,
 

beets/dbcore/types.py

@@ -75,6 +75,12 @@ class Type(object):
         """
         return self.normalize(sql_value)
 
+    def to_sql(self, model_value):
+        """Convert a value as stored in the model object to a value used
+        by the database adapter.
+        """
+        return model_value
+
 
 # Reusable types.
 

beets/library.py

@@ -109,6 +109,11 @@ class PathType(types.Type):
         else:
             return value
 
+    def to_sql(self, value):
+        if isinstance(value, str):
+            value = buffer(value)
+        return value
+
 
 class MusicalKey(types.String):
     """String representing the musical key of a song.
@@ -188,7 +193,6 @@ class WriteError(FileOperationError):
 class LibModel(dbcore.Model):
     """Shared concrete functionality for Items and Albums.
     """
-    _bytes_keys = ('path', 'artpath')
 
     def _template_funcs(self):
         funcs = DefaultTemplateFunctions(self, self._db).functions()