The Database

Introduction

In chapter Getting Started, you learned how to access a relational database. In section Sending to Database, you used a <FixedQuerySender> to apply a query to a database. This sender had the following attribute: datasourceName="jdbc/${instance.name.lc}". This is how you referenced the database. In this section you will learn what is happening behind the scenes. You need this knowledge when you want to set up your own database instead of relying on the Frank!Runner. You will also learn how to work with multiple databases.

How the database is accessed

To understand the attribute datasourceName="jdbc/${instance.name.lc}", you first have to understand property instance.name.lc, see subsection Frank!Framework Properties. Each instance of the Frank!Framework must define a property instance.name. The Frank!Framework automatically calculates property instance.name.lc by taking the value of instance.name and replacing uppercase letters with lowercase letters. For example, if instance.name is MyApp, then instance.name.lc becomes myapp. In this case, the shown attribute is equivalent to datasourceName="jdbc/myapp".

Your deployed configuration thus uses a database that is referenced by the name jdbc/myapp (or jdbc/otherapp if instance.name would be OtherApp). The name jdbc/myapp is a Java Naming and Directory Interface (JNDI) name. JNDI names allow you as a developer to reference a database without defining the database name, the database user and the password. You do not have to include sensitive information in your Frank config and it can easily be deployed on different environments that each may have their own database. It is up to the system administrator to link each JNDI name in your Frank config to a concrete database, a concrete database user, a concrete password etc. You can see an example in subsection Migrate the database.

This knowledge allows you to use multiple databases. If you have a second database then give it a JNDI name, say jdbc/alternative. The senders and listeners that access the database all have an attribute datasourceName. Set this attribute within your Frank config, datasourceName="jdbc/alternative", every time you want to access your second database. It is up to the system administrator to link this JNDI name to her own database.

Warning

The Frank!Runner (see section Frank!Runner) does not support multiple databases. This tool automates deploying the Frank!Framework and it automatically creates a database for your Frank. You cannot use this project to connect to an existing database or to use multiple databases.

If you are using an Apache Tomcat application server, then the Frank!Framework expects that there is a database with JNDI name jdbc/${instance.name.lc} with ${instance.name.lc} a property reference as explained. The expected database name depends on property instance.name.

Initial data

The Frank!Framework uses Liquibase to populate your database with tables and with initial data. In your Frank config you include a file DatabaseChangelog.xml that defines what tables you want to create and what initial data you want. You can provide this information in SQL statements or in pure XML, the latter being database agnostic. See https://www.liquibase.org/ to learn how to write DatabaseChangelog.xml. You saw an example in chapter Getting Started, section Database Initialization. Your initial data is split into change sets, each wrapped within XML element <changeSet>.

Liquibase allows multiple deployments of your Frank to share the same database. Liquibase maintains database tables to remember what change sets have been processed. If one instance applies a change set, the others will see that the change set has been applied. Each instance only applies change sets not yet processed, which causes each change set to be executed only once. This approach only works if change sets are never altered. When you update your Frank config, please do not change existing change sets but append new ones.

Note

If you want to undo initialization by Liquibase, you can execute SQL query DROP ALL OBJECTS in the JDBC | Execute Query screen.

If you have multiple databases, what database is selected? By default, it is the database with JNDI name jdbc/${instance.name.lc}. You can override this by setting property jdbc.migrator.dataSource.

The Frank!Framework only does database initialization when property jdbc.migrator.active is true. There is a subtle point with this property. It has a different effect as a system property or classpath property on the one hand, or as a configuration property on the other hand. The Frank!Framework needs database tables to perform some advanced services like the message store (not yet explained in the Frank!Manual). These tables are only created when the Frank!Framework starts with property jdbc.migrator.active set as a system property or classpath property. If jdbc.migrator.active is only set within a configuration, then these system tables are not created and some advanced features of the Frank!Framework will not work.

When jdbc.migrator.active is true for a configuration, then that configuration can always create and initialize its own database tables using a DatabaseChangelog.xml. This is the case when jdbc.migrator.active is a system property, a classpath property or a configuration property.