Merge pull request #3089 from pprkut/delayed_type_casting

Performance improvement: Type cast properties on demand

beets/dbcore/db.py

@@ -91,6 +91,100 @@ class FormattedMapping(Mapping):
         return value
 
 
+class LazyConvertDict(object):
+    """Lazily convert types for attributes fetched from the database
+    """
+
+    def __init__(self, model_cls):
+        """Initialize the object empty
+        """
+        self.data = {}
+        self.model_cls = model_cls
+        self._converted = {}
+
+    def init(self, data):
+        """Set the base data that should be lazily converted
+        """
+        self.data = data
+
+    def _convert(self, key, value):
+        """Convert the attribute type according the the SQL type
+        """
+        return self.model_cls._type(key).from_sql(value)
+
+    def __setitem__(self, key, value):
+        """Set an attribute value, assume it's already converted
+        """
+        self._converted[key] = value
+
+    def __getitem__(self, key):
+        """Get an attribute value, converting the type on demand
+        if needed
+        """
+        if key in self._converted:
+            return self._converted[key]
+        elif key in self.data:
+            value = self._convert(key, self.data[key])
+            self._converted[key] = value
+            return value
+
+    def __delitem__(self, key):
+        """Delete both converted and base data
+        """
+        if key in self._converted:
+            del self._converted[key]
+        if key in self.data:
+            del self.data[key]
+
+    def keys(self):
+        """Get a list of available field names for this object.
+        """
+        return list(self._converted.keys()) + list(self.data.keys())
+
+    def copy(self):
+        """Create a copy of the object.
+        """
+        new = self.__class__(self.model_cls)
+        new.data = self.data.copy()
+        new._converted = self._converted.copy()
+        return new
+
+    # Act like a dictionary.
+
+    def update(self, values):
+        """Assign all values in the given dict.
+        """
+        for key, value in values.items():
+            self[key] = value
+
+    def items(self):
+        """Iterate over (key, value) pairs that this object contains.
+        Computed fields are not included.
+        """
+        for key in self:
+            yield key, self[key]
+
+    def get(self, key, default=None):
+        """Get the value for a given key or `default` if it does not
+        exist.
+        """
+        if key in self:
+            return self[key]
+        else:
+            return default
+
+    def __contains__(self, key):
+        """Determine whether `key` is an attribute on this object.
+        """
+        return key in self.keys()
+
+    def __iter__(self):
+        """Iterate over the available field names (excluding computed
+        fields).
+        """
+        return iter(self.keys())
+
+
 # Abstract base for model classes.
 
 class Model(object):
@@ -180,8 +274,8 @@ class Model(object):
         """
         self._db = db
         self._dirty = set()
-        self._values_fixed = {}
-        self._values_flex = {}
+        self._values_fixed = LazyConvertDict(self)
+        self._values_flex = LazyConvertDict(self)
 
         # Initial contents.
         self.update(values)
@@ -195,10 +289,10 @@ class Model(object):
         ordinary construction are bypassed.
         """
         obj = cls(db)
-        for key, value in fixed_values.items():
-            obj._values_fixed[key] = cls._type(key).from_sql(value)
-        for key, value in flex_values.items():
-            obj._values_flex[key] = cls._type(key).from_sql(value)
+
+        obj._values_fixed.init(fixed_values)
+        obj._values_flex.init(flex_values)
+
         return obj
 
     def __repr__(self):
@@ -259,7 +353,10 @@ class Model(object):
         if key in getters:  # Computed.
             return getters[key](self)
         elif key in self._fields:  # Fixed.
-            return self._values_fixed.get(key, self._type(key).null)
+            if key in self._values_fixed:
+                return self._values_fixed[key]
+            else:
+                return self._type(key).null
         elif key in self._values_flex:  # Flexible.
             return self._values_flex[key]
         else:
@@ -439,8 +536,8 @@ class Model(object):
         self._check_db()
         stored_obj = self._db._get(type(self), self.id)
         assert stored_obj is not None, u"object {0} not in DB".format(self.id)
-        self._values_fixed = {}
-        self._values_flex = {}
+        self._values_fixed = LazyConvertDict(self)
+        self._values_flex = LazyConvertDict(self)
         self.update(dict(stored_obj))
         self.clear_dirty()