Statistics queries with time range for PostgreSQL and Hibernate

Few days ago I was asked to implement charts with some finance data using JS charting library, in the application working on Postgres database. There's a lot of finance stuff in the database stored every minute and I just needed to show this data on charts.

OK, but charts are nice if you can restrict amount of your data returned from the server to some limited number of items. Returning 1000 items would both - make chart very heavy and unreadable and consume a lot of net traffic. I assumed 50 as the average number of items that are nicely displayed on such charts and are also acceptable from the traffic point of view.

It would be nice to split time data to some periods that always assert no more than 50 items and then return only such statistics to the client side. And here I discovered very nice and applicable postgres function, which is date_trunc.

Equipped with this weapon I figured out universal solution to calculate such time-based statistics for postgres database using Hibernate. Firstly I designed a very simple enum to calculate right time-grouping criteria:

It'd be nice then to have everything working with whatever entity type and to be able to customize grouping query with Hibernate criteria, because this is right abstraction to build SQL query step by step from filters hypothetically associated with chart filters:

It's also quite simple to autodetect best data granulation for the chart (eg. if it is a hour, day, month or something else) depending on the base time range for the chart.

Modal windows available by URL binding in AngularJS with ui-bootstrap and ui-router

It's well known how ui-bootstrap supports modal windows. These modals don't have any URL and cannot be accessed by URL, though. This is very good, because they should stay as the main view subview only, don't mess with the browser history and first and foremost they shouldn't kill underlying main view controller, what would reset its current state (like filters applied, pagination, etc). This would be a problem using URL-based modals, especially with ui-router which seems to be a standard for now.

On the other hand it's good to have a URL-bound modals for one usage. When you send to people notification emails with links to perform the requested action. I mean such emails like "Attention, you have to do something in the application. You can do it with this link.". In typical scenario this action is already available in the application, usually on modal window. You just want to send this modal link to the user, to trigger requested action, and if you can't bind your modal to the URL, you can only send him some more or less awkward message, like "Use this link to login to the application, and then ... dig yourself to find where you can do it.".

Here is a little ui-router hack to achieve both things - normal, unobtrusive modals, and URL bindings.

NOTE, that this is not about having modals with ui-router URL address. There're many implementations on stackoverflow, and also example in ui-router FAQ. But these solutions have a very big flaw - their modals kill underlying main view controller, and when you're back, you're really back (like with the back button) on the main view with new controller instance and reset whole state, what is unnacceptable for real world applications. Maybe next time I'll think a little about how to achieve this point without this problem, but now it's about having normal bootstrap modals also bound to URL addresses in ui-router.

Firstly, you need to define in your main HTML the location where the modal will be rendered, if it's URL-bound. Let's make it simple as modal.html (all codes are inserted at the bottom of this post). You can define surrounding view as main view, and use it for the modal target (when the modal window is rendered) or the whole application layout target (for views other than modal windows) by appropriate router substates configuration and CSS.

Afterwards, let's define simple module.js with modal content, one URL parameter and resolve function that provides the resolved object to the modal controller, from the server side. At this point your modal is exposed at /modal/{ID} URL, and you may use it in your notification emails.

Now, let's support our modal as the regular ui-boostrap modal for other application views. This is done in modal.service.js by simple hack and moving parameters from ui-router configuration to ui-bootstrap $modal instance. In any view now, instead of calling $modal, you can call modalService(viewName, stateParams) to open your modal window previously defined in ui-router configuration, and at the same time you have this modal available by URL.

Source code

Distributed hibernate search with ApacheMQ and Spring

This catching title will be not about distributed hibernate search, but something really close :)

The case I've recently solved was a quite different. I have a frontend application that uses hibernate database and hibernate search, and then I needed to add additional application - let's call it an integration server, which exposes some API webservices for the overall system. Integration server uses the same database as the frontend application, and enables clients to put data to the database using its webservices. Both applications exist on two different physical servers, as well.

Everything looks simple unless you start thinking about hibernate search update from the integration server, while the index is located solely on the frontend application side, because only this part of the system uses it. When you put data to the database from the integration server, the frontend application full-text index is not updated, of course. I've been looking for simple solution to overcome this problem.

Firstly, let's take a look at what the hibernate search proposes. It supports distributed hibernate search index, with master-slave replication, where all nodes are connected using JMS. This solution was something I didn't really need because only one node uses the index for searching. Moreover this solution is based on periodical index replication, what causes the index is up-to-date on each node only after some interval. Finally, I didn't like this solution because it uses JNDI, what is not really Spring way to solve the problems (I don't really like JEE, I only like to work with lighweight Java application stacks).

So I figured out the solution with following prerequisites:

1. I don't want to use replication because I only need to use search on frontend application side.
2. I want to keep index physically on the side really using it, ie. on the frontend application side.
3. When the integration server updates database data, I need to update the index.
4. I don't want to use JNDI.
5. We are already using ApacheMQ, I want to use it for this solution as well. AMQ broker is already located on the integration server side.

OK, let's delve into the solution. Here is the spring config of important beans on the frontend side:

What do we have here? Standard hibernate session factory on which I'm showing the hibernate search config, that creates and uses local lucene index. Then AMQ connection factory, that connects to the broker running somewhere else. Nothing special. The only interesting bean is RemoteHibernateSearchController, which is derived from standard AbstractJMSHibernateSearchController, that already is a JMS message listener, and only needs to provide hibernate sesssion from our session factory:

Now let's take a look at integration server config, which is a little more interesting:

Same session factory, but configured in the other way. As the backend we use AMQBackendQueueProcessor - our own implementation, shown for a while, not the standard "lucene" implementation. Our implementation will delegate all hibernate search insert/update requests to the listnening frontend RemoteHibernateSearchController, through the JMS queue named "queue.search".

I need to mention here a thing. The integration server doesn't use hibernate search for searching at all (it is only insert/update oriented). But if we have enabled hibernate session for integration server, we need to have at least some index to work. This index won't be updated ever (AMQBackendQueueProcessor will delegate all updates to frontend index through JMS) and will never be read. So I decided to use "ram" provider, which holds whole this few-bytes index in RAM memory. You can, anyway, use any implementation you want - this is only a fake index.

AMQ configuration comes then, and we define only one queue here (this config is redundant, but you can add some parametrization to the config made this way). This is the part really starting the broker using TCP transport (in test environment both servers are run on localhost). Note, that AMQ connection factory connects to the (local) broker using VM transport, and doesn't start its own broker itself.

Now few words about the initialization order. We will use a little trick to bind AMQBackendQueueProcessor to Spring for a while, so the order is important. When session factory bean creates the session factory, hibernate search worker backend needs to be able to work right away. Our backend will work using AMQ, so AMQ needs to be initialized before the session factory bean is initialized. In the example it is done by depends-on attribute, and sessionFactory bean depends here on amqBroker bean (indirectly, the dependency goes through appContextProvider bean, which is also required to be initialized when session factory bean starts).

ApplicationContextProvider bean just accomplishes the commons hack to access Spring beans from non-spring aware code:

And finally AMQBackendQueueProcessor overrides JNDI-related code of standard JmsBackendQueueProcessor JMS connection factory lookup with spring-based implementation, using our container config and appContextProvider hack: