Azure Table Storage - How to query entities with a filter on non initialized fields.

Question

Hey Azure experts.

If I understand well, azure table storage entities are similar to a Hashtable containing <string, object> pairs. Therefore when I add a new field 'LastActivityTimestamp' to my entity, all previously created entites will have null for that field.
My question is how do I get all entities that have 'LastActivityTimestamp' == null ?

I tried the following query but Azure returns "One of the request inputs is not valid." in the HTTP response :
this.DataContext.Chatters.Where(chatter => chatter.LastActivityTimestamp == null || chatter.LastActivityTimestamp < minDateTime).AsEnumerable();

If I do this query : this.DataContext.Chatters.Where(chatter => chatter.LastActivityTimestamp < minDateTime).AsEnumerable();
then it returns only the entities that statisfy the filter AND have a non null value.

Any help much appreciated.

Answer 1

Hi Clement,

You can't check if an element is null simply because if an element's value is null, it won't be stored in table storage (remember it's not a conventional table). Only exception to this is the PartitionKey, RowKey & TimeStamp elements.

Hope this helps.

Thanks

Gaurav Mantri
Cerebrata Software
http://www.cerebrata.com/

Answer 2

Hi Gaurav.

So are you saying that the only way to retrieve entities for which the new field is not initialized to is retrieve all entities and then test the field from the client app ??

Answer 3

Hi Clement,

I don't think that is also not possible because even if you retrieve all entities, you will not get the desired attribute if it does not exist. One possible solution could be to get all entities and check if that particular attribute exists in your entity set or not. If that attribute does not exist in an entity, that would be the entity you want to know about.

Hope this helps.

Thanks

Gaurav Mantri
Cerebrata Software
http://www.cerebrata.com/