==================
DAO interfaces
==================

.. contents:: Contents
   :depth: 4

A Data Access Object (DAO) is an interface that provides structured access to databases.

DAO definition
==================

DAOs are defined as interfaces annotated with ``@Dao``.

Implementation classes for the DAO interfaces are automatically generated by the annotation processor during compilation.

Query definition
==================

:doc:`query/index` can be defined using annotations.

You can use :doc:`query-builder/index` or :doc:`query-dsl` in a :ref:`dao-default-method` when you need to build queries dynamically in Java code.

.. _dao-default-method:

Default method
==================

You can write Java code freely in default methods.

You can get the ``Config`` instance associated with a DAO instance by calling ``Config.get`` with the DAO instance as an argument.


.. code-block:: java

  @Dao
  public interface EmployeeDao {

      default int count() {
          Config config = Config.get(this);
          SelectBuilder builder = SelectBuilder.newInstance(config);
          builder.sql("select count(*) from employee");
          return builder.getScalarSingleResult(int.class);
      }
  }

Example
==================

Implementation classes are automatically generated by the annotation processor during compilation.
These implementation classes can be directly instantiated and used.
However, if the configuration class is managed by a Dependency Injection (DI) container, the DI container should control the instantiation of the implementation classes.

.. code-block:: java

  Config config = ...;
  EmployeeDao employeeDao = new EmployeeDaoImpl(config);
  Employee employee = employeeDao.selectById(1);

By default, the implementation class name is the interface name suffixed with ``Impl``.
Please refer to :doc:`annotation-processing` for information on how to customize the package name and suffix.

A DAO interface does not need to be defined in a one-to-one relationship with an entity class.
One DAO interface can handle multiple entity classes.

.. code-block:: java

  @Dao
  public interface MyDao {

      @Select
      Employee selectEmployeeById(int id);

      @Select
      Department selectDepartmentByName(String name);

      @Update
      int updateAddress(Address address);
  }