Add BigAutoField for BlockCompletion primary key.

openedx/core/djangolib/fields.py

@@ -5,7 +5,9 @@ from django.db import models
 
 
 class CharNullField(models.CharField):
-    """CharField that stores NULL but returns ''"""
+    """
+    CharField that stores NULL but returns ''
+    """
 
     description = "CharField that stores NULL but returns ''"
 
@@ -26,3 +28,31 @@ class CharNullField(models.CharField):
             return None
         else:
             return value
+
+
+class BigAutoField(models.AutoField):
+    """
+    AutoField that uses BigIntegers.
+
+    This exists in Django as of version 1.10.
+    """
+
+    def db_type(self, connection):
+        """
+        The type of the field to insert into the database.
+        """
+        conn_module = type(connection).__module__
+        if "mysql" in conn_module:
+            return "bigint AUTO_INCREMENT"
+        elif "postgres" in conn_module:
+            return "bigserial"
+        else:
+            return super(BigAutoField, self).db_type(connection)
+
+    def rel_db_type(self, connection):
+        """
+        The type to be used by relations pointing to this field.
+
+        Not used until Django 1.10.
+        """
+        return "bigint"