SOA – How to Share Data Between Web Applications

databasesoa

I have two web applications, say Application_1 and Application_2.

Application_2 has a database table named table_2, which changes infrequently, and needs to be accessed by Application_1.

Does it make sense to create a table_2 table in Application_1 and update it with an ETL task?

A straightforward solution would be expose the data through a REST API in Application_2, but this will break the decoupling between both applications and introduce a new point of failure in Application_1.

Best Answer

Since you tagged the question with SOA, I suspect that you're thinking the right answer might be using a service interface. Such a service interface should not expose the data, but the functionality you want to provide as a contract to be exposed by one application and consumed by the other application.

As the question is being asked in the abstract, this contract could range anywhere from providing answer to a very specific lookup to an event stream notifying the consumer of changes.

Either application (i.e. on either or both sides of the service interface) can make use of caching (copy of table) if they need to, but caching is an optimization that should not be prematurely applied.

Either way, these applications are coupled. The ETL job you suggest will also couple the applications and probably result in a more poorly understood contract between the them than a well-designed service interface.

Related Solutions

Web and API – Reusing Business Logic

I've encountered this before (many times) and what I've ended up doing preferring is:

Take the BL out of the website. Make the website a consumer of the API. Treat the website as just some other client of your API. Your API IS the service.

If you find yourself thinking that you need special API methods just for the website, think again! If its good for the goose, it is good for the gander. If you really really really need special functionality for the website I would suggest that what you've really found is a difference in "user profile" and therefore this is a situation where the API should still support the "special" functions, but then you control them via authorisation.

Not convinced?

Take the paradigm a step further ...

The phone app is running on a platform where bytecode is executed, the app lives in the phone and consumes API services via HTTP/JSON

The website is an app running on a platform where HTML+Javascript is the executed, the app lives in a the browser and consumes API services via HTTP/JSON

Same same!

Extend that to tablets, TVs, other phone platforms, plugins, third party apps, mashups, ...

Lots of different user experiences all plugged into a common API.

Your app IS the API. The website is just one client (of many)

Database – NHibernate and complex domain model against a legacy database

Unfortunately I don't know much about AutoMapper but I can offer a solution to your second question. Fluent NHibernate is a tool to aide with your NHibernate mappings, allowing you to configure them in a programmatic way rather using than XML. One of the methods you can call when setting up your mappings is DiscriminateSubClassesOnColumn() which allows you to specify the database column that will be used to create your sub-classes. Then in your sub-classes you specify the DiscriminatorValue which can be an enum.

Here is what I imagine your mappings to look like (untested code):

public class ProgramMap : ClassMap<Program>
{
    public ProgramMap()
    {
        //map your fields as normal, eg: Map(p => p.Id), Map(p => p.Name)
        DiscriminateSubClassesOnColumn<int>("Episode");
    }
}

public class MovieeMap : SubclassMap<Movie>
{
    public MovieMap()
    {
        DiscriminatorValue(0);
    }
}

The problem may actually be specifying the DiscriminatorValue for your Movies but hopefully this gives you something to go on. For reference I've used the following links to put this answer together so they may be worth a look in case I've missed something out.

Note that if you don't specify the DiscriminatorValue, Fluent NHibernate assumes that the discriminator column contains your class name (which would be a terrible database design!).

Best Answer

Related Solutions

Web and API – Reusing Business Logic

Database – NHibernate and complex domain model against a legacy database

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