Allow File-like objects to be stored.

No longer demands FileField be an actual instance of file, but instead
checks whether object has a 'read' attribute. Fixes read() on
GridFSProxy to return an empty string on read failure, or None if file
does not exist.

mongoengine/fields.py

@@ -875,10 +875,14 @@ class GridFSProxy(object):
         self.newfile.writelines(lines)
 
     def read(self, size=-1):
-        try:
-            return self.get().read(size)
-        except:
+        gridout = self.get()
+        if gridout is None:
             return None
+        else:
+            try:
+                return gridout.read(size)
+            except:
+                return ""
 
     def delete(self):
         # Delete file from GridFS, FileField still remains
@@ -935,7 +939,7 @@ class FileField(BaseField):
 
     def __set__(self, instance, value):
         key = self.name
-        if isinstance(value, file) or isinstance(value, str):
+        if (hasattr(value, 'read') and not isinstance(value, GridFSProxy)) or isinstance(value, str):
             # using "FileField() = file/string" notation
             grid_file = instance._data.get(self.name)
             # If a file already exists, delete it

tests/fields.py

@@ -2,6 +2,7 @@ import datetime
 import os
 import unittest
 import uuid
+import StringIO
 
 from decimal import Decimal
 
@@ -1481,6 +1482,21 @@ class FieldTest(unittest.TestCase):
         self.assertEquals(result.file.read(), text)
         self.assertEquals(result.file.content_type, content_type)
         result.file.delete() # Remove file from GridFS
+        PutFile.objects.delete()
+
+        # Ensure file-like objects are stored
+        putfile = PutFile()
+        putstring = StringIO.StringIO()
+        putstring.write(text)
+        putstring.seek(0)
+        putfile.file.put(putstring, content_type=content_type)
+        putfile.save()
+        putfile.validate()
+        result = PutFile.objects.first()
+        self.assertTrue(putfile == result)
+        self.assertEquals(result.file.read(), text)
+        self.assertEquals(result.file.content_type, content_type)
+        result.file.delete()
 
         streamfile = StreamFile()
         streamfile.file.new_file(content_type=content_type)