From 61e43787d238e20c40bef1769aa7e092dcf2daf0 Mon Sep 17 00:00:00 2001
From: Adrian Sampson <adrian@radbox.org>
Date: Sat, 11 Oct 2014 12:18:12 -0700
Subject: [PATCH] Second-order optimizations to Results getters

Fix #997. This provides shortcuts for len() and subscripting in certain
situations. There are of course more shortcuts that are possible, but this
will do for now!
---
 beets/dbcore/db.py | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/beets/dbcore/db.py b/beets/dbcore/db.py
index 07e64d1bb..723e07ce9 100644
--- a/beets/dbcore/db.py
+++ b/beets/dbcore/db.py
@@ -480,6 +480,7 @@ class Results(object):
 
         self._objects = []  # Model objects materialized *so far*.
         self._row_iter = iter(self.rows)  # Indicate next row to materialize.
+        self._materialized = False  # All objects have been materialized.
 
     def _get_objects(self):
         """Construct and generate Model objects for they query. The
@@ -495,7 +496,7 @@ class Results(object):
         for object in self._objects:
             yield object
 
-        # Now, for the rows that have not yet been processed, materialize
+        # Next, for the rows that have not yet been processed, materialize
         # objects and add them to the list.
         for row in self._row_iter:
             obj = self._make_model(row)
@@ -505,6 +506,10 @@ class Results(object):
                 self._objects.append(obj)
                 yield obj
 
+        # Now that all the rows have been materialized, set a flag so we
+        # can take a shortcut in certain other situations.
+        self._materialized = True
+
     def __iter__(self):
         """Construct and generate Model objects for all matching
         objects, in sorted order.
@@ -540,6 +545,9 @@ class Results(object):
     def __len__(self):
         """Get the number of matching objects.
         """
+        if self._materialized:
+            return len(self._objects)
+
         if self.query:
             # A slow query. Fall back to testing every object.
             count = 0
@@ -560,6 +568,9 @@ class Results(object):
         """Get the nth item in this result set. This is inefficient: all
         items up to n are materialized and thrown away.
         """
+        if self._materialized and not self.sort:
+            return self._objects[n]
+
         it = iter(self)
         try:
             for i in range(n):