The new guy and his database

This is a followup to two previous articles about Agile databases and Migrations for Java. It tries to examplify some of the stuff I talk about in those two articles. Here we go again… 🙂

You won’t get a new developer each week, but the scenario will help illustrate how the tools I have been talking about works. The examples below are loosely based on the previous setup we had in a previous project, but should be general enough to give you an idea. This basically means SubVersion, Maven, Oracle and Ant.

So you have a new developer. Let’s call him John. He’s quite nervous the first day of work, and you wan’t to pair program with him to get him right into coding. Sure he could read the architecture documents, but you will touch upon most of the architecture by working together, so you’d rather just get started.

You sit down with the new developer, and tell him to check out the project from SubVersion.

svn co http://companyrepo/project/trunk project-trunk

The checkout pulls down several Maven projects, with a common parent POM. First things first, so you compile everything and make sure he can use it in Eclipse.

mvn install eclipse:eclipse -DdownloadSources=true

Depending on your location downloading dependencies can take a while. So showing him the coffe machine would probably be a good thing right about now. Everything compiles, and he imports it all into Eclipse.

Now he is eager to have a look at the application, but like most applications your application needs a database. You could probably have settled for HsqlDB or H2 in a test setting, but I prefer to do manual testing on the product that we are actually going to deploy to in production.

So you need to initialize a database. One of the sub-projects you checked out earlier is actually a separate database project. Inside this project is a folder where the scripts for the database resides. On your wiki he finds a description on how to initialize a new database. From the base project he does:

1. cd dbproject/src/sql/baseline
2. sqlplus sysadm/syspw@//db:1521/service @create_new_schema.sql johnuser testpw
3. sqlplus johnuser/testpw@//db:1521/service @baseline_data.sql
4. sqlplus johnuser/testpw@//db:1521/service @test_data.sql
5. cd ../../ (takes him to the dbproject folder)
6. ant dbdeploy-upgrade -Ddb.user=johnuser -Ddb.pw=testpw -Ddb.host=db -Ddb.service=service

Now John has a fully functional database that he can use as his local sandbox for development. I guess a little bit of explaining is in order. In the lines above with sqlplus commands, the first parameter is connection settings. The second parameter is the script to execute, and everything after that are parameters to the script. On line 2 the script uses the inputs to create a user and schema called johnuser and with the testpw password. It also creates tables, triggers, functions etc.

After creating the complete schema in line 2, the baseline data is inserted. I am not sure if this is a good term, but by baseline data I mean data that needs to be there for the system to operate, and don’t change during normal processing. You might have a admin interface to change it, but for most of the time they stay the same. This could be tables holding countries or postal codes.

After inserting some baseline data, it is time to insert some test data in step 3, such that John has something to experiment with right out of the box. This is separated in a script because not all environments will need those data.

The last step is done to upgrade the database to the latest version. See the migrations article for an explanation of the concept. This means that the baseline script is not updated with changes all the time. Every now and again we generate a new baseline from the production database, so we can delete some of the old migrations. Generating a new baseline is something I havn’t really found a good tool for yet, so I get the DBA to do it with some of his tools. It happens rarely enough that for now, I accept that it’s not automated.

That really is the last part of my database articles for now. It is a topic I will probably write more about later as it is something that has been handled poorly in most projects I haven been in. It is also an important part of what I like to call agile deployment that helps us reduce the time spent on deploying, and fixing all those pesky little errors we do when deploying.