ListProperty equals to <null> and makes entity unreadable - Google App Engine

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Message from discussion ListProperty equals to <null> and makes entity unreadable
Date: Thu, 1 Nov 2012 10:40:15 -0700 (PDT)
From: jay_m <yov...@gmail.com>
To: google-appengine@googlegroups.com
Message-Id: <89742edf-9354-4e8e-ae55-3bbae0e0d296@googlegroups.com>
Subject: ListProperty equals to <null> and makes entity unreadable
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A few days ago I ran some data migration process that resulted in a few 
number pf oddities that I am trying to fix with. Here's my situation - I 
hope one of you out there could help. 

Background:
My app had a User model with two StringPropertyList properties representing 
a 1:many relationship between a user and an Item model. The properties, 
completed_items & in_progress_items, held the key_name of an Item model. 
Every time and Item model was created, I also added its key_name to the 
User who created it.

Since these lists grew to contain several hundred of items, I decided to 
migrate their data into two new models: UserCompletedItem & 
UserInProgressItem. Each model holds the item key_name and the user 
key_name. As part of the migration, I ran on all User entities, fetched the 
user's completed_items & in_progress_items lists and for each item I 
created a new UserCompletedItem / UserInProgressItem. After creating all 
new entities, I set the  completed_items & in_progress_items properties to 
empty lists (User.completed_items=[] & User.in_progress_items model=[]) to 
reduce the size of each User entity. 

In addition to that, I removed from the code any reference 
to User.completed_items or User.in_progress_items and all data access 
activities are performed using the two new models. 

The problem:
When I look at the User entities using GAE's Admin's Data Viewer, the value 
of the two properties that I set to [] appear as <missing> (an indication 
that the process of setting an empty list actually worked). However, for a 
small number of entities, the two properties equal to <null>. In addition 
to that, in my code, whenever I try to fetch an entity with a <null> value, 
the following exception gets thrown and the fetch fails:
*Error_type:<class 'google.appengine.api.datastore_errors.BadValueError'> ; 
Error_message: Property in_progress_item is required*
My question, how can I fetch these entities with <null>? Is there a way to 
change the <null> values to []? 

Alternatively, can I remove the two properties from the Model class (since 
I am not going to reference them in the code anymore) and things will work 
normally?

Thanks,
-jay

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A few days ago I ran some data migration process that resulted in a few num=
ber pf oddities that I am trying to fix with. Here's my situation - I hope =
one of you out there could help.&nbsp;<div><br></div><div>Background:</div>=
<div>My app had a&nbsp;User model with two StringPropertyList properties re=
presenting a 1:many relationship between a user and an Item model. The prop=
erties, completed_items &amp; in_progress_items, held the key_name of an It=
em model. Every time and Item model was created, I also added its key_name =
to the User who created it.</div><div><div><br></div><div>Since these lists=
 grew to contain several hundred of items, I decided to migrate their data =
into two new models: UserCompletedItem &amp; UserInProgressItem. Each model=
 holds the item key_name and the user key_name. As part of the migration, I=
 ran on all User entities, fetched the user's&nbsp;completed_items &amp; in=
_progress_items&nbsp;lists and for each item I created a new&nbsp;UserCompl=
etedItem / UserInProgressItem. After creating all new entities, I set the&n=
bsp;&nbsp;completed_items &amp; in_progress_items&nbsp;properties to empty =
lists (User.completed_items=3D[] &amp;&nbsp;User.in_progress_items&nbsp;mod=
el=3D[]) to reduce the size of each User entity.&nbsp;</div><div><br></div>=
<div>In addition to that, I removed from the code any reference to&nbsp;Use=
r.completed_items or&nbsp;User.in_progress_items&nbsp;and all data access a=
ctivities are performed using the two new models.&nbsp;</div></div><div><br=
></div><div>The problem:</div><div>When I look at the User entities using&n=
bsp;GAE's Admin's Data Viewer, the value of the two properties that I set t=
o [] appear as &lt;missing&gt; (an indication that the process of setting a=
n empty list actually worked). However, for a small number of entities,&nbs=
p;the two properties equal to &lt;null&gt;. In addition to that, in my code=
, whenever I try to fetch an entity with a &lt;null&gt; value, the followin=
g exception gets thrown and the fetch fails:</div><div><h1 class=3D"ha" sty=
le=3D"font-family: arial, sans-serif; margin-top: 12px; margin-right: 1px; =
margin-bottom: 9px; padding-left: 8px; background: inherit; border-right: i=
nherit; line-height: normal; "><span id=3D":s" class=3D"hP" style=3D"paddin=
g-right: 10px; "><font size=3D"2"><b>Error_type<wbr>:&lt;class 'google.ap<w=
br>pengine.ap<wbr>i.datastor<wbr>e_errors.B<wbr>adValueErr<wbr>or'&gt; ; Er=
ror_mess<wbr>age: Property in_progress_item&nbsp;is required</b></font></sp=
an></h1></div><div>My question, how can I&nbsp;fetch these entities with &l=
t;null&gt;? Is there a way to change the &lt;null&gt; values to []?&nbsp;<b=
r></div><div><br></div><div>Alternatively, can I remove the two properties =
from the Model class (since I am not going to reference them in the code an=
ymore) and things will work normally?</div><div><br></div><div>Thanks,</div=
><div>-jay</div><div><span class=3D"hP" style=3D"padding-right: 10px; "><di=
v></div></span></div>
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