codegen

codegen

Use the Hibernate Tools library to codegen Java source code (entities) from an existing database schema.

Description

The Hibernate Tools project contains various tools that make your Hibernate development more sophisticated. These tools are generally geared to support a suite of Eclipse IDE plugins, but they can be used in a headless way. That's exactly what the hibernate-playground/codegen does. It uses the hibernate-tools-orm library to generate Hibernate entity classes (Java source code). Specifically, it does this by creating a simple Gradle plugin and task named hibernateCodeGen. In fact, the Hibernate Tools project defines Ant tasks and a Maven plugin for doing the same thing. I want to use Gradle, so I modeled my plugin after those but ignored all extensibility features because this plugin is just for me.

Instructions

Follow these instructions to run the demo:

1. Pre-requisites: Java 21, Docker
2. Start the Postgres database:

   • docker compose up --renew-anon-volumes --detach

   • This will start the database and initialize the schema and sample data.
3. Codegen the entity classes
   • This step is only needed if you have changed the database schema. For example, if you added a new column to an existing table, then you'll need to regenerate the Java entity class for that table so that it can map to that column. This project hooks into the Hibernate Tools codegen library by way of a Gradle plugin and task. Run the following command to generate the entity code.

   • ./gradlew hibernateCodeGen

4. Run the program:

   • ./gradlew run

   • Altogether, it should look like this:

   • $ ./gradlew run
     
     21:24:05 [main] WARN org.hibernate.orm.connections.pooling - HHH10001002: Using built-in connection pool (not intended for production use)
     21:24:06 [main] DEBUG org.hibernate.SQL - 
         /* <criteria> */ select
             o1_0.id,
             o1_0.observation,
             o1_0.type,
             ot1_0.id,
             ot1_0.description 
         from
             public.observations o1_0 
         join
             public.observation_types ot1_0 
                 on ot1_0.id=o1_0.type
     21:24:06 [main] INFO dgroomes.codegen.App - The Criteria-based query found results...
     21:24:06 [main] INFO dgroomes.codegen.App - Observation (id=1, type=Uninteresting observation): The sky is blue
     21:24:06 [main] INFO dgroomes.codegen.App - Observation (id=2, type=Interesting observation): The speed of light can circle the earth 7 times in a second
     21:24:06 [main] INFO dgroomes.codegen.App - 
     

5. Stop the database:

   • docker compose down

Wish List

General clean-ups, TODOs and things I wish to implement for this project:

• DONE Use a Gradle version catalog (TOML)

Reference

• Hibernate Tools docs