I've added a Session ndb class to models.py. The fields are:
- name, speakerKeys, session_type and location are StringProperty type. we want these fields to be indexed.
- speakerKeys is repeated as there can be multiple speakers for a session, speakers need to be created to get this key.
- highlights is of TextProperty type, we don't need this field to be indexed.
- start_time is an IntegerProperty type. I've tried to use a TimeProperty but ran into problems as ndb saves those differently to a standard python datetime.time(). This added complexity and made the application harder to maintain with a lot of code just used to convert times for the queries. I'm using an integer representation of 24h time HHMM (e.g. 1245 is 12:45).
- date is a DateProperty
- duration is IntegerProperty in number of minutes.
The ProtoRPC message classes are SessionFormIn a copy of the session class in string format, SessionFormOut the outbound message form, where the speakers names are added to improve human readability, and SessionForms a repeated SessionFormOut message.
I've implemented speakers as a new entity. Speakers must be created with createSpeaker before being used in a session. Speakers have a name and one or more organisations.
createSession has the same structure as createConference. I use a _createSessionObject function to get the user profile and the conference object. The conference is the parent of the session which makes querying for all sessions of a conference easy with an ancestor query. I check if the session date is within the dates of the conference. After storing the session, a task is added for the featured speaker functionality, this is discussed later.
getConferenceSessions is a straightforward ancestor query with ordering by date and time. It takes a websafe conference key in the url path.
getConferenceByType is a query with a filter on session_type
getSessionBySpeaker is also a query with filter across all sessions of all conferences.
createSpeaker creates a new speaker, speakers have no parents, and can be created and used by any user. This allows speakers to be used in different conferences.
getSpeaker returns the speaker's information.
I've implemented wishlists as another property of the Profile class. It's similar to the conferenceKeysToAttend property, a repeated StringProperty where we add the session keys.
addSessionToWishlist takes a session key in the url path. It calls _wishlistAddition. This function gets the profile of the registed user, checks if the session is in the wish-list and appends the websafe session key to the list. _wishlistAddition also takes an optional argument - addition, if set to False it removes the sessionKey from the wishlist. This is used by the removeSessionFromWishlist endpoint.
getSessionInWishlist returns the list of sessions in the user's wishlist.
querySessions is a general query endpoint that allows to query on any field. It can be used with a websafe Conference Key, in which case it limits the query to the session of that conference. If the websafeConferenceKey field is left empty, then the query will be on all sessions across conferences the user is registered for. This endpoint only allows for one filter at a time.
doubleQuerySession is also a general query endpoint. It allows queries on two fields of the session class with any operator. It allows two inequalities on different fields.
The doubleQuerySession endpoint is a solution to the query problem. For this we can't use ndb for queries with inequalities on two different properties. So the function runs the first query and if the operators of both queries are inequalities, the second query is done in memory by the function, looping through the results of the first query. We can easily imagine situations where this wouldn't be practical, when the size of the result of the first query would be too large. But for our example, even very large conferences can only have so many sessions so it shouldn't be a problem.
Since doubleQuerySession queries on multiple properties we need to make sure the multi-property indices are built and listed in index.yaml. I've run queries on each pair of properties on the local development server. This is a bit tedious but is a good way to test the app.
For this functionality, I've added a line to _createSessionObject. When a new session is created, it adds a task to the taskqueue: is_speaker_featured. When this task is executed, each speaker for the newly created session is checked, if the speaker is already in another session he becomes the featured speaker. The featured speaker and session name are stored in memcache.
To get all the speakers for a conference we use _getSpeakers. This function gets all the speakers for a conference. I've also added another endpoint using this function getConferenceSpeakers.
getFeaturedSpeaker just gets the featured speaker and session name from the memcache, and returns a StringMessage.