As discussed in the last post, we are going to apply a layered architectural structure, to the World of Art web app. The first layer we are going to develop, will be called the Data Model Layer. The purpose of this layer is to achieve a separation of concerns. To create distance and independence, between code supporting the application’s user interface, and code supporting access to the data source.
We will begin by adding an object model to the application. This object model is based on the World Of Art Relational Database, developed in a prior iteration. See Generating Data Model Based on Relational Database, for step by step instructions on generating the data model. As mentioned in previous posts, our data model layer is based on the Microsoft ADO.NET Entity Framework.
Now that the data model is generated, I’m going to display another illustration of the World of Art database diagram, which the data model is bases on. This diagram is more detailed, and shows the properties of each column of the two tables, currently in the database. Also, remember the “one-to-many” relationship between an artist and their works of art. An artist can create one or more works of art. This relationship is illustrated by the key and infinity symbols in the diagram. Please keep this diagram in mind, when we examine the data model diagram, based on this database.
The next diagram illustrates the data model, which is based on the World of Art database. I used the Entity Data Model Wizard in Visual Studio 2010, to generate the data model. The data model has two classes, based on the two tables in the World of Art database. The Artist table and the Works of Art table, have been abstracted into two separate classes. The columns of the tables are now represented by the properties of each class. Also, notice how the one-to-many relationship between an artist and their works of art is maintained.
The Entity Data Model Wizard in Visual Studio 2010, not only generates the entity data model diagram illustrated above, it also generates an entire C# code file, which the diagram is based on. The following image is a class diagram I generated in Visual Studio 2010. It’s based on the WorldOfArt.Designer.cs file which was generated by the Entity Data Model Wizard. As you can see, the wizard actually generated three classes. The one in the middle is the WorldOfArtContext class, it inherits the System.Data.Objects.ObjectContext class. The other two classes are based on the two tables in the World of Art database, and inherit the System.Data.Objects.DataClasses.EntityObject class. Like any typical C# class, they have private members and public properties, along with a wide range of partial methods and event handlers, for updating the tables.
Finally, lets take a look at the World Of Art solution in Visual Studio, with the newly added Data Model layer. The highlighted folder, in the illustration below, represents the Data Model Layer in the World of Art project solution. The folder contains two files;
- The WorldOfArt.edmx file, is the data model diagram. It can be viewed and modified, in the Entity Data Model Designer, in Visual Studio.
- The WorldOfArtDesigner.cs file, is the C# source code of the Entity Data Model.
In my next post, I’ll discuss the benefits derived from building a Data Model Architectural Layer, and an Entity Data Model.