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Cayenne Modeler
The CayenneModeler is a user interface that generates the Cayenne object model. It parses the existing database schema and stores the information about the database into a DataMap. The DataMap is an XML file and has enough information in it to regenerate the database schema if needed. The DataMap is used by the CayenneModeler to generate Java DataObejcts that are used by the Cayenne runtime.
Installation
Installation is fairly simple—just download the binaries and include the cayenne.jar in the classpath. To run the Cayenne modeler, you first need to set the JAVA_HOME and the CAYENNE_HOME. Run modeler.bat to start the CayenneModeler.
A Working Example
As an example, suppose you have a simple database schema that has four tables: customer, employee, product, and sales. Check the source code download (.war file) for the DDL (cayenne.sql). The DDL was built for a MySQL database. Once the database tables are setup, you can work with CayenneModeler to generate the Cayenne code.
Before creating a new project, make sure the classpath for your database driver is correctly set in the preferences panel. Before starting the reverse engineering process, make sure an appropriate DataAdapter is chosen. In this case, it should be com.objecstyle.cayenne.dba.mysql.MySQLAdapter.
To reverse-engineer the database:
- Start the CayenneModeler
- Create a DataDomain, say SampleDataDomain
- Add a DataNode to it, say SampleDataNode
- Configure the DataSource
- Add a DataMap, say SampleDataMap
- Select the DataMap and choose Tools—>Reverse Engineer Database Schema
CayenneModeler converts and stores all the database information in the SampleDataMap as DbEntities and ObjEntities. DbEntities are exact representations of the underlying database tables and views while ObjEntities are object-oriented representations of the same.
Now you're ready to generate the data access classes in Cayenne. Select DbEntity and choose the primary key generation strategy. Here, choose 'Database-generated' as the strategy because the MySQL tables have auto-increment primary keys. If you're not sure, you may leave the value as 'default', Cayenne will choose the best strategy for you.
Now, check the attributes. CayenneModeler should have mapped each table attribute to a corresponding Java datatype. You will also notice that the foreign keys have been converted as regular fields. This is because Cayenne wants you to decide what the relationships should be. To have a truly object-oriented access to the data, you need to think in terms of objects and not in terms of primary keys and foreign keys (which are relational in nature). For this reason, you'll have to make some changes to the ObjEntities to make these relationships work.
Next, modify the Relationships tab. A relationship represents how each entity is associated with another entity. For instance, one or more sales records can be associated with any customer in the customer table. Similarly, a product can be associated with one or more records in the sales table. Select the sales DBEntity and create a new relationship called toCustomer. Select the new relationship and create a database mapping by entering toCustomer as the relationship and 'sales' as the as the reverse mapping. Next, identify the fields in both the tables on which the join must be made. In this case, it will be id from the sales table and id from the customer table. Now, create new relationships for byEmployee from the sales table to the employee table and ofProduct from the sales table to the employee table.
Finally, choose Project—≫Validate Project from the menu bar to validate the relationships. Once the project is validated, you can generate the class files. Keeping SampleDataMap selected, choose Tools—≫Generate Classes and provide the path to the output directory. By default, the CayenneModeler generates Cayenne system classes for each table and extends this class and provides an extended class for your use. You can add any business specific validations or logic into the derived classes without affecting the generated classes.
CayenneModeler generates three configuration files (cayenne.xml, SampleDomainMap.map.xml, and SampleDomainNode.driver.xml)
and eight Java class files including four super classes (Customer.java, _Customer.java, Employee.java, _Employee.java, Product.java, _Product.java, Sales.java, and _Sales.java)
This completes the generation process of Cayenne; next you will try to use the generated code in an actual application.
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