When you already have a database and you want to use JPA or Hibernate to access that database you need something that will generate those POJO classes for you with the appropriate annotations. There are some existing solutions but I was not happy with them, so this is Yet Another Pojo Generator.
The generator gets generates as part of the build of DomUI and can be found as utilities/hibernate-generator/target/hibernate-generator.jar, and can be executed as:
java -jar hibernate-generator.jar
The generator so far should work for PostgreSQL and Oracle, with PostgreSQL the one that has been tested. Adding new database types should not be too hard.
The generator does the following:
- It generates a new POJO class for every table in the schema(s) specified
- If a POJO class already exists for the table it edits the POJO file and updates it with the database definition:
- New columns are added to the existing POJO
- Removed columns are, well, removed
- Metadata is updated where applicable
- Existing code in POJO classes is mostly left alone, so it should be reasonably safe to re-run the generator on already existing code.
- It has basic support for compound primary keys; it should properly generate XxxxId classes for class Xxxx if that table as a compound primary key
- It adds all relations that are properly defined by foreign keys
- It adds @ManyToOne parent references in the child class
- It adds @OneToMany child list references as List<T> in the parent, with T the type of the child class
- This however will not work for compound PK's.
- It automatically recognizes and uses any @MappedSuperClass class as a base class for those tables that share colums with that base class.
- It generates/updates [classname].properties files with the new properties in the class, so that these files can be used as resource bundles for the property names of that class.
- It generates a class HibernateConfigurator which contains methods that add all classes to Hibernate's config.
An example command line invocation would be:
This connects to a PostgreSQL database with the specified username and passwords, loads all tables from the schema's pdi_meta, source_mapping, auth and sectormodel, then generates/updates all classes into the specified directory and package.
The directory and package are separate, so the final directory for the classes is formed by adding the source AND the package name.
The options supported are:
|-db||Database connection string as username:password@hostname[:port]/databasename (required)|
|-dbtype||The database type: postgres or oracle (required)|
|-source||Specifies the root of the source directory for both existing and generated sources|
|-pkg||The package name for the generated classes|
|-destroy-constructors||When set, this destroys all constructors in existing Java classes. It can be used to get rid of the silliness generated by the hibernate pojo tool|
|-ffr||When set all field names are forcefully renamed to the name as decided by column name and prefix.|
|-frm||When set all getter and setter methods in existing classes are renamed to whatever the property name is calculated to be|
|-nb, -no-bundles||Disable generation of .properties bundles|
|-no-baseclass||Do not try to find base classes for new pojo's|
|-no-deserial||Postgres 'serial' columns are actually just columns with a 'default' which retrieves a value from a generated sequence. By default the code will find this sequence and generate a SEQUENCE type of ID generator. Setting this option will cause the code to use the generated.IDENTITY method.|
|-no-onechar-boolean||By default, all columns found that are (var)char with a size of 1 and that contain <= 2 distinct values are generated as boolean with an appropriate @Type annotation. This option disables that.|