What is DAO factory pattern?

The DAO Factory Pattern (Data Access Object Factory Pattern) is a design pattern that abstracts and encapsulates all interactions with data sources. It separates data access logic from business logic, resulting in more modular code that is easier to manage and maintain.

1. Data Access Object Interface (DAO Interface): This is an interface that defines data access operations, such as CRUD operations. The implementation of this interface is dependent on the specific data source.

2. Data Access Object Implementation (DAO Implementation): This is the concrete implementation of the above interface. Depending on the data source (e.g., MySQL, Oracle, or MongoDB), different implementations may be used.

3. DAO Factory: This is a factory class responsible for creating and returning concrete DAO implementations. It typically includes a method that returns the appropriate DAO implementation based on the input parameters (e.g., database type).

4. Entity Class: These classes represent database tables and contain properties and methods corresponding to the table columns.

Example Application

Consider an application that needs to support multiple databases (e.g., MySQL and Oracle). Specific DAO implementations can be created for each database. Upon application startup, the DAO factory determines which concrete implementation to instantiate based on the database type specified in the configuration file.

For example, in managing user information, we might have the following interfaces and implementations:

• Interface: UserDAO, which defines methods such as addUser and getUserById.
• MySQL Implementation: MySQLUserDAO, which implements the UserDAO interface and handles MySQL-specific operations.
• Oracle Implementation: OracleUserDAO, which implements the UserDAO interface and handles Oracle-specific operations.

The DAO factory includes a method like getUserDAO that returns the corresponding UserDAO implementation based on the database type parameter.

This design allows for easy addition of new database types by adding new DAO implementations and modifying the factory method, without altering existing business logic. It improves code maintainability and enhances system extensibility.