Query flexible attributes already in _fetch()

This resolves the query length and potential security problems,
while keeping the performance benefits.

beets/dbcore/db.py

@@ -32,7 +32,6 @@ from beets.dbcore import types
 from .query import MatchQuery, NullSort, TrueQuery
 import six
 
-
 class DBAccessError(Exception):
     """The SQLite database became inaccessible.
 
@@ -524,7 +523,8 @@ class Results(object):
     """An item query result set. Iterating over the collection lazily
     constructs LibModel objects that reflect database rows.
     """
-    def __init__(self, model_class, rows, db, query=None, sort=None):
+    def __init__(self, model_class, rows, db, flex_rows,
+                 query=None, sort=None):
         """Create a result set that will construct objects of type
         `model_class`.
 
@@ -544,6 +544,7 @@ class Results(object):
         self.db = db
         self.query = query
         self.sort = sort
+        self.flex_rows = flex_rows
 
         # We keep a queue of rows we haven't yet consumed for
         # materialization. We preserve the original total number of
@@ -569,8 +570,7 @@ class Results(object):
         # First fetch all flexible attributes for all items in the result.
         # Doing the per-item filtering in python is faster than issuing
         # one query per item to sqlite.
-        item_ids = [row['id'] for row in self._rows]
-        flex_attrs = self._get_flex_attrs(item_ids)
+        flex_attrs = self._get_indexed_flex_attrs()
 
         index = 0  # Position in the materialized objects.
         while index < len(self._objects) or self._rows:
@@ -609,20 +609,11 @@ class Results(object):
             # Objects are pre-sorted (i.e., by the database).
             return self._get_objects()
 
-    def _get_flex_attrs(self, ids):
-        # Get the flexible attributes for all ids.
-        with self.db.transaction() as tx:
-            id_list = ', '.join(str(id) for id in ids)
-            flex_rows = tx.query(
-                'SELECT * FROM {0} WHERE entity_id IN ({1})'.format(
-                    self.model_class._flex_table,
-                    id_list
-                )
-            )
-
-        # Index flexible attributes by the entity id they belong to
+    def _get_indexed_flex_attrs(self):
+        """ Index flexible attributes by the entity id they belong to
+        """
         flex_values = dict()
-        for row in flex_rows:
+        for row in self.flex_rows:
             if row['entity_id'] not in flex_values:
                 flex_values[row['entity_id']] = dict()
 
@@ -631,6 +622,8 @@ class Results(object):
         return flex_values
 
     def _make_model(self, row, flex_values={}):
+        """ Create a Model object for the given row
+        """
         cols = dict(row)
         values = dict((k, v) for (k, v) in cols.items()
                       if not k[:4] == 'flex')
@@ -920,11 +913,23 @@ class Database(object):
             "ORDER BY {0}".format(order_by) if order_by else '',
         )
 
+        # Fetch flexible attributes for items matching the main query
+        flex_sql = ("""
+            SELECT * FROM {0} WHERE entity_id IN
+                (SELECT id FROM {1} WHERE {2});
+            """.format(
+                model_cls._flex_table,
+                model_cls._table,
+                where or '1',
+            )
+        )
+
         with self.transaction() as tx:
             rows = tx.query(sql, subvals)
+            flex_rows = tx.query(flex_sql, subvals)
 
         return Results(
-            model_cls, rows, self,
+            model_cls, rows, self, flex_rows,
             None if where else query,  # Slow query component.
             sort if sort.is_slow() else None,  # Slow sort component.
         )