Object/Relational Mapping (ORM) is a technique that maps object-oriented classes and properties to relational database tables and fields. ORM leverages existing object-oriented programming skills and provides an abstraction layer over databases. There are important differences between ORM and traditional data access approaches like ADO.NET in areas like data binding, business logic implementation, and support for multi-tier architectures.

1. Object/Relational Mapping in real-world applications

5. Data Binding ADO.NET Data Binding DataTables, DataSets – query results ADO.NET ORM Data Binding? Name City Mike Reading Ruth Liverpool Sue London Brad Birmingham Jim Newcastle

6. Data Binding ORM ADO.NET Fetch data IList IBindingList ITypedList ... ORM Fetch data Name City Mike Reading Ruth Liverpool Sue London Brad Birmingham Jim Newcastle

7. Business Logic ADO.NET SQL Stored procedures (T-SQL, ...) Trigger code ... ADO.NET, SQL code Functionality Functionality Functionality must be implemented in different models, using different programming languages.

8. Business Logic ORM SQL Stored procedures (T-SQL, ...) Trigger code ... ORM Functionality on the server implemented in .NET ORM leverages existing knowledge and skills related to OO programming and unifies the programming model ORM can provide a level of abstraction towards the database Functionality Functionality Functionality is implemented in the same model, using the same programming language.

12. Important for Business Logic! Expectations regarding data consistency could be different when ORM is being used: suddenly data has to be consistent even if it lives “only” in RAM! Whether or not this is relevant for you depends on your use case.

14. Multi-Tier with ADO.NET Network – XML WebServices, WCF, ... Serialization Deserialization Result: Identical data! Name City Mike Reading Ruth Liverpool Sue London Brad Birmingham Jim Newcastle Name City Mike Reading Ruth Liverpool Sue London Brad Birmingham Jim Newcastle

16. Multi-Tier with ORM Dynamic SQL Network Metadata Transport format Transport format / SQL Persistent Classes / Query classes / Transport format Persistent Classes Layer Data used ORM Optional! Application The application works with persistent classes and calls functionality of the ORM system. On this layer, the ORM system provides most of its services – Identity Map, Transaction handling, ... The transport format defines Data Transfer Objects (DTOs). This layer is optional – it’s used when “Dynamic SQL” is a separate tier. Finally the ORM system dynamically generates SQL code.