From b3b3285a703226e551e34a89e59a0c6c4e97b16f Mon Sep 17 00:00:00 2001
From: Eevee <git@veekun.com>
Date: Fri, 31 Jul 2009 00:03:02 -0700
Subject: [PATCH] Improved CSV import speed by several orders of magnitude.

---
 pokedex/__init__.py | 85 ++++++++++++++++++++++++++++++++---------------------
 1 file changed, 51 insertions(+), 34 deletions(-)

diff --git a/pokedex/__init__.py b/pokedex/__init__.py
index e142ae6..1e6c6d1 100644
--- a/pokedex/__init__.py
+++ b/pokedex/__init__.py
@@ -27,8 +27,7 @@ def command_csvimport(engine_uri, directory='.'):
 
     from sqlalchemy.orm.attributes import instrumentation_registry
 
-    # Use autocommit in case rows fail due to foreign key incest
-    session = connect(engine_uri, autocommit=True, autoflush=False)
+    session = connect(engine_uri)
 
     metadata.create_all()
 
@@ -74,11 +73,18 @@ def command_csvimport(engine_uri, directory='.'):
         reader = csv.reader(csvfile, lineterminator='\n')
         column_names = [unicode(column) for column in reader.next()]
 
-        # Self-referential tables may contain rows with foreign keys of
-        # other rows in the same table that do not yet exist.  We'll keep
-        # a running list of these and try inserting them again after the
-        # rest are done
-        failed_rows = []
+        # Self-referential tables may contain rows with foreign keys of other
+        # rows in the same table that do not yet exist.  Pull these out and add
+        # them to the session last
+        # ASSUMPTION: Self-referential tables have a single PK called "id"
+        deferred_rows = []  # ( row referring to id, [foreign ids we need] )
+        seen_ids = {}       # primary key we've seen => 1
+
+        # Fetch foreign key columns that point at this table, if any
+        self_ref_columns = []
+        for column in table_obj.c:
+            if any(_.references(table_obj) for _ in column.foreign_keys):
+                self_ref_columns.append(column)
 
         for csvs in reader:
             row = table_class()
@@ -101,33 +107,44 @@ def command_csvimport(engine_uri, directory='.'):
 
                 setattr(row, column_name, value)
 
-            try:
-                session.add(row)
-                session.flush()
-            except IntegrityError, e:
-                failed_rows.append(row)
-
-        # Loop over the failed rows and keep trying to insert them.  If a loop
-        # doesn't manage to insert any rows, bail.
-        do_another_loop = True
-        while failed_rows and do_another_loop:
-            do_another_loop = False
-
-            for i, row in enumerate(failed_rows):
-                try:
-                    session.add(row)
-                    session.flush()
-
-                    # Success!
-                    del failed_rows[i]
-                    do_another_loop = True
-                except IntegrityError, e:
-                    pass
-
-        if failed_rows:
-            print len(failed_rows), "rows failed"
-        else:
-            print 'loaded'
+            # May need to stash this row and add it later if it refers to a
+            # later row in this table
+            if self_ref_columns:
+                foreign_ids = [getattr(row, _.name) for _ in self_ref_columns]
+                foreign_ids = [_ for _ in foreign_ids if _]  # remove NULL ids
+
+                if not foreign_ids:
+                    # NULL key.  Remember this row and add as usual.
+                    seen_ids[row.id] = 1
+
+                elif all(_ in seen_ids for _ in foreign_ids):
+                    # Non-NULL key we've already seen.  Remember it and commit
+                    # so we know the old row exists when we add the new one
+                    session.commit()
+                    seen_ids[row.id] = 1
+
+                else:
+                    # Non-NULL future id.  Save this and insert it later!
+                    deferred_rows.append((row, foreign_ids))
+                    continue
+
+            session.add(row)
+
+        session.commit()
+
+        # Attempt to add any spare rows we've collected
+        for row, foreign_ids in deferred_rows:
+            if not all(_ in seen_ids for _ in foreign_ids):
+                # Could happen if row A refers to B which refers to C.
+                # This is ridiculous and doesn't happen in my data so far
+                raise ValueError("Too many levels of self-reference!  "
+                                 "Row was: " + str(row.__dict__))
+
+            session.add(row)
+            seen_ids[row.id] = 1
+            session.commit()
+
+        print 'loaded'
 
 def command_csvexport(engine_uri, directory='.'):
     import csv
-- 
2.7.4