– Narayanaswamy, Sysfore
The goal of the DAL development is to strengthen the middle-tier in the application, i.e. to implement business logic in Java. The DAL provides the application developer with the following functionality:
- Type safe querying and retrieval of business objects from the database.
- A convenient API to update or create new data in the database.
- A type safe interface to update information of a business object, increased productivity by making the properties of a business object directly visible through getters and setters (in the IDE).
- Transaction and context handling.
- Security and validation checking.
- Automatically maps new entries in the Application Dictionary to database tables and columns.
- Generates Java class business objects (and their associations) on the basis of the Application Dictionary model.
The DAL consists of a development-time and runtime part. The development-time part takes care of generating Java business object classes. The runtime part takes care of mapping Java classes to the database and supporting functionality such as security and validation.
2 DAL Architecture
The Data Access Layer (DAL) provides an API to store, query and remove business objects from the database.
The DAL offers three main services to instantiate, create and query Openbravo ERP business objects: OBDal, OBCriteria and OBProvider. The service classes can all be found in the org.openbravo.dal.service package.
The OBDal instance (available through OBDal.getInstance()) is the main entrance point for retrieving and storing business objects in the database in a validated and secure way. It provides the following functions:
- save: stores a new business object in the database or an existing business object is updated. For existing business object it is not required to call this method as Hibernate does automatic dirty checking.
- get: retrieves a single business object using its id. There are two versions: one using the class name (of the generated business object) and one using the entity name.
- remove: delete a business object from the database, the actual database delete is done at commit time.
- create OBCriteria: OBCriteria objects are used for querying.
- commitAndClose and rollbackAndClose: these methods can be used to implement custom transaction handling. Normally this is done by the environment (Openbravo web container or Openbravo test).
The OBDal API makes extensive use of the OBCriteria and OBQuery classes to support querying.
The OBCriteria class implements the Hibernate Criteria interface. It extends the standard Hibernate Criteria functionality for filtering on active, client and organization. In addition it offers convenience methods to set orderby and to perform count actions.
- Summarizing, the OBCriteria object supports all Hibernate Criteria features:
- Setting the where-clause of a filter using the Hibernate Criterion concept.
- Setting paging parameters such as first row and maximum number of results.
- Setting order by on the query.
- Specifying joins for performance reasons.
- Performing counts, average etc.
The OBQuery class is an extension of the Hibernate Query object. It extends the standard Hibernate Query functionality for filtering on active, client and organization.
The OBQuery object is created through the OBDal.createQuery method. The first argument of the createQuery is a class or an entity name, the second argument is the where-clause.
Openbravo business objects should not be instantiated directly using the new operator. Instead the OBProvider class should be used to create an instance of the required business object. The OBProvider is located in the org.openbravo.base.provider package and can be retrieved using the method OBProvider.getInstance(). The OBProvider offers methods to instantiate using a class name or using an entity name.