I'm working on the datastore of google app engine, and I'm developing an app for manage events.
I have 2 entity:
- user
- event
- attribute eventDate
A user can follow one or more event, so I create the link table
- UserEvent
-User key
-Event key
My problem is that I would like to have a list of the events followed by the user, ordered by eventDate.
How can I do?
I found 3 solution, but I don't like anyone...
Query on all the event ordered, and then iterate and choose only the
one with has one occurency on UserEvent (I don't like because
probably I will have thousand of event, but a user follow only
few..)
Query on all the user event (filtered by userKey) and put the result
in an ordered list (I don't like because I have to load all Event at
once, without pagination)
Add in table UserEvent the attribute eventDate (I don't like because
if an event has 3000 followers I have to do 3000 update...)
Thank you
Alessandro
If you really don't like such denormalization, consider using CloudSQL.
If you always query events for a given user, you can consider storing a ListProperty of Events in the User entity.
- user
- attribute eventList []key
You will be limited by the maximum size of an entity (currently 1MB) and if the list is indexed your're limited to 5000 entries.
Related
I am working on a social networking project with cassandra. Users can subscribe to a profile and have access to the list of people who have subscribed to that same profile. My goal is to retrieve in a table called user_follows the list of people subscribed to a profile.
CREATE TABLE users_follows (to_id text, from_id text, followed_at timestamp, PRIMARY KEY(to_id, from_id))
The problem is that some profiles can have thousands of subscribers and I don't want to get them all at once. That's why I'd like to get the list in increments of 20 depending on how far down the user goes. My problem is that I can't see how to retrieve the other parts of the list after the first select because Cassandra always returns the same users.
SELECT * FROM users_follows where to_id = 'xxxxx'
A possible solution was to sort with a timestamp but in case I want to retrieve the list of people to whom a user is subscribed (the reverse query) this would not work. One solution would be to use materialized views but I'm not sure that it would be very optimal given the size of the table. Or to create a different table, one user_follows and another user_followers, but I don't think this is very recommended....
I am trying to think of a way to design the firestore db in a way that is efficient.
The main issue I am having with is how I should define "groups". Lets say a user is invited to a group chat and so the client needs to retrieve the data for that group chat, should I have a "groups" collection and then find the correct group document? OR, should I have a "groups" property in the user document that has a id to reference the group to retrieve?
In SQL, having a reference in a user's groups table would be the obvious answer, but I am not sure about firestore. I don't want to look through the entire collection of groups just to find the group that the user was newly invited in. Any tips? Also, my front end is in React and I am considering using the onSnapshot method to subscribe to the collection (that seems to be the best way to have real time updates).
What i believe is best for you is this :
First have a collection, suppose you make groups, and inside that every docuent has all the group unique ids,
And inside that for every group, i.e document, you can have a collection which holds all the chats for that group and group related info , like group type, etc etc
Hope it helps. feel free for doubts
I have two models: Members and Events. A member can participe in many events and in an event, there are many participants. I think about like this:
class Members(ndb.model):
event = ndb.KeyProperty(repeated=True)
class Events(ndb.model):
member = ndb.KeyProperty(repeated=True)
What's the best way to do many-to-many relationship?
I think in this case you want to have an array/list of keys in one model pointing to the other model. Since there is a limit on the length of the array/list (the max is 5000 right now) you probably want to have the member model point to the events models (I am assuming members probably don't go to many events (more than 5000), but there are many (more than 5000) members at an event). Now if you want the list of attendees you just query for the event key in the members models. You can do a key only query if you just want the head count, this will save on cost.
If for some reason you need to have both cases be over 5000, then you can make another (attendee) model that contains a member key and an event key, then make this attendee model for each guest for each event. To get the list of guests just query this model for a specific event, if you need a list of events for a member do the opposite. This isn't much more work than the above so might be your go to way of doing it even if 5000 isn't a limiting factor.
I want to create a multi-select Contact Lookup.
What i want :
When user clicks on a lookup then he should be able to select multiple contacts from that.
What i have done:
I have created an object and a field inside that object using both
"Lookup" and
"MasterDetail Relationship" and
"Junction Object"
When i try to use this Field for any input text/Field then it always provides an option to select only one value from lookup but i want to have an option to select multiple.
Even in the Junction object i have created 2 master-detail relationships still lookup allows only one value to be selected.Moreover it makes the field mandatory which i don't want.
Links that i followed:
http://success.salesforce.com/questionDetail?qId=a1X30000000Hl5dEAC
https://ap1.salesforce.com/help/doc/user_ed.jsp?loc=help§ion=help&hash=topic-title&target=relationships_manytomany.htm
Can anybody suggest me how to do this.
Its same as we use Email CC/BCC under Send Email option for any Lead.
Even you use a junction object a lookup is just that, it references (looks up to) one other record: when you create a record on the junction object you still have to set each lookup individually and you're still creating only one record.
Master Detail relationships are essentially lookups on steroids, one object becomes the child of the other and will be deleted if the parent object is deleted, they're not going to provide an interface to lookup to many records at once.
If you're not a developer then your best bet is to either just create on junction object record at a time, or look into using dataloader. You could prepare your data in Excel or similar and then upload all the records into Salesforce in one go.
If you are a developer, or have developers at your disposal, then what we've done in the past is create a Visualforce page to do the job. So if, for example, you wanted to link a bunch of contacts up to an Account, we'd have a single account lookup field on the page, then some search fields relating to fields on the contact. Using a SOQL query you can then find all contacts matching the search parameters and display them in a list, where you may want to provide checkboxes to allow the user to select the contacts they want. Then it's just a case of looping through the selected contacts, setting their Account field to be the chosen account.
There are areas in Salesforce (such as the send Email functionality you mentioned) where it's clear to see that bespoke work has been done to fulfil a specific task — another instance of what you want is in the area where you can manage campaign members. This is the model I've copied in the past when implementing a Visualforce page as described.
Good luck!
For adding multiple junction objects at one time, the only solution we have found is a custom Visualforce page, as described by LaceySnr.
For a slightly different problem, where we need to assign many of object B to object A, We have trained our users to do this with a view on object B. We are assigning Billing Accounts (B) to Payment Offices (A). The view on Billing Account has check boxes on the left side. The user checks the Billing Accounts to be assigned, then double-clicks on the Payment Office field on any of the checked rows. A pop-up asks if you want to update only the single row or all checked rows. By selecting 'all checked rows', the update is done to all of them.
The view is created by the user, who enters the selection criteria (name, address, state, etc.). All user-created views are visible only to them.
I am working on a system, which will run on GAE, which will have several related entities and I am not sure of the best way to store the data. This post is a request for advice from others who may have similar experience....
The system will have users, with profile data and an image. Those users will be able to create "events" and add journal entries to it. For the purpose of the system, the "events" will likely have 1 or 2 journal entries in them, and anything over 10 would likely never happen. Other users will be able to add comments to users' entries as well, where popular ones may have hundreds or even thousands of comments. When a random visitor uses the system, they should be able to see the latest events (latest, being defined by those with latest journal entries in them), search by tag, and a very perform basic text search. Then upon selecting an event to view, it should be displayed with all journal entries, and all user comments, with user images alongside comments. A user should also have a kind of self-admin page, to view/modify/delete their events and to view/modify/delete comments they have made on other events. So, doing all this on a normal RDBMS would just queries with some big joins across several tables. On GAE it would obviously need to work differently. Here are my initial thoughts on the design of the entities:
Event entity - id, name, timstamp, list
property of tags, view count,
creator's username, creator's profile
image id, number of journal entries
it contains, number of total comments
it contains, timestamp of last update to contained journal entries, list property of index words for search (built/updated from text from contained journal entries)
JournalEntry entity - timestamp,
journal text, name of event,
creator's username, creator's profile
image id, list property of comments
(containing commenter username and
image id)
User entity - username, password hash, email, list property of subscribed events, timestamp of create date, image id, number of comments posted, number of events created, number of journal entries created, timestamp of last journal activity
UserComment entity - username, id of event commented on, title of event commented on
TagData entity - tag name, count of events with tag on them
So, I'd like to hear what people here think about the design and what changes should be made to help it scale well. Thanks!
Rather than store Event.id as a property, use the id automatically embedded in each entity's key, or set unique key names on entities as you create them.
You have lots of options for modeling the relationship between Event and JournalEntry: you could use a ReferenceProperty, you could parent JournalEntries to Events and retrieve them with ancestor queries, or you could store a list of JournalEntry key ids or names on Event and retrieve them in batch with a key query. Try some things out with realistically-distributed dummy data, and use appstats to see what works best.
UserComment references an Event, while JournalEntry references a list of UserComments, which is a little confusing. Is there a relationship between UserComment and JournalEntry? or just between UserComment and Event?
Persisting so many counts is expensive. When I post a comment, you're going to write a new UserComment entity and also update my User entity and a JournalEntry entity and an Event entity. The number of UserComments you expect per Event makes it unwise to include everything in the same entity group, which means you can't do these writes transactionally, so you'll do them serially, and the entities might be stored across different network nodes, making the whole operation slow; and you'll also be open to consistency problems. Can you do without some of these counts and consider storing others in memcache?
When you fetch an Event from the datastore, you don't actually care about its list of search index words, and retrieving and deserializing them from protocol buffers has a cost. You can get around this by splitting each Event's search index words into a separate child EventIndex entity. Then you can query EventIndex on your search term, fetch just the EventIndex keys for EventIndexes that match your search, derive the corresponding Events' keys with key.parent(), and fetch the Events by key, never paying for the retrieval or deserialization of your search index word lists. Brett Slatkin explains this strategy here at 14:35.
Updating Event.viewCount will fail if you have a lot of views for any Event in rapid succession, so you should try out counter sharding.
Good luck, and tell us what you learn by trying stuff out.