problem改用_id作为搜索用主键；submission更加statistic_info字段

submission/migrations/0003_auto_20170704_1243.py

@@ -0,0 +1,24 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9.6 on 2017-07-04 12:43
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('submission', '0002_auto_20170509_1203'),
+    ]
+
+    operations = [
+        migrations.RenameField(
+            model_name='submission',
+            old_name='accepted_info',
+            new_name='statistic_info',
+        ),
+        migrations.RemoveField(
+            model_name='submission',
+            name='accepted_time',
+        ),
+    ]