BANGALORE, INDIA: Often developers need to understand the database before they can write access codes for it. Understanding complex database structure that is controlled by administrator becomes a bottleneck in application development cycle. Using Microsoft's ADO.NET Entity Framework, developers can create an entity relationship model of the database (ie SQL Server) inside Visual Studio 2008. This conceptual model is then used by developers to write code against database and that in turn reduces code development time along with lines of code. This is a step by Microsoft to increase abstraction, making things efficient for developers.
Consider this example: when we write code to access data from a database (SQL Server), we often have to write queries containing 'Joins,' which can only be used if there is complete understanding of the underlying database structure. Another issue is regarding writing 'connection strings' to connect and disconnect from database. Here is a sample code that shows how developers normally write the code:
using System.Data.SqlClient;
SqlConnection conn = new SqlConnection( "Data Source=(local);Initial Catalog=Northwind;Integrated Security=SSPI");
SqlDataReader rdr = null;
conn.Open();
SqlCommand cmd = new SqlCommand("select * from database", conn);
rdr = cmd.ExecuteReader();
rdr.Close();
conn.Close();
In this code, developer is spending too much time on database related issues. The real aim behind developing application logic is delayed. ADO.NET Entity Framework along with LINQ tries to address these issues making application development simple and quick.
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To create EDM of the 'School' database click on 'Project>Add New Item'. From the list select 'ADO.NET Entity Data Model' and change the name to 'School.edmx'.
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Implementing ADO.NET Entity Framework
In this section we will show how to use ADO.NET entity framework feature for existing database and how it simplifies the above code. Before you actually start using this feature, you should have Visual Studio 2008 SP1 installed on your system. We will start with creating a 'Windows Form Application' project in VS by the name of 'PCQLADOEF.' We shall use C# as the programming language. Once the project has been created, we will add an 'ADO.NET Entity Data Model' item to the project. This can be done by clicking on 'Project' and then on 'Add New Item.' This action will start a wizard; from this wizard select the appropriate database to create the entity model. Here we used 'School' database.
Now once the wizard finishes, you shall have the 'School.edmx' file created. Double clicking on this file will show the model in the Designer window. This is very helpful in understanding the structure of database in question. To understand the EDMX file more, right click on 'School.edmx' and open it with 'XML Editor'. There are three major portions of this file: Conceptual Model, Storage Model and Mappings. EntityType represents the table along with properties defining different fields and Association represents relationship of entity. Storage Model is the representation of database schema and Mappings defines movement between conceptual layer and actual storage. One can easily push back the changes made to conceptual layer to actual database by writing a single line of code.
