Understanding Data Access Objects

Rather than placing data-specific logic in business objects, all data-specific logic is placed in data access objects instead. At runtime, a data access object is attached to a Business Object when an attempt is first made to retrieve or update data.

Generic Data Access Classes

mmDataAccessBase is an abstract base class from which all data access classes in MM .NET are derived. The following UML class diagram shows the different data access classes that are found in MM .NET:

When a business object needs to access data from a SQL Server database, it uses the mmDataAccessSql class. When it needs to access data from an Oracle database it uses mmDataAccessOracle, and so on.

Custom Data Access Classes

If you are using Entity Framework, there is no need to create a custom data access class. However, if you are using classic ADO.NET, and you use stored procedures for retrieving and updating data, you need to create a custom data access that knows how to properly call these stored procedures. For example, this OrderDetail business object has an associated OrderDetailDataAccess class:

The MM .NET Business Layer Generator can automatically generate custom data access classes for you, as well as stored procedures for retrieving and updating data. For details, see the Help topic under Using the MM .NET Business Layer Generator, Step 4: Data Access Layer Options.