Access Redshift Data with Entity Framework 6

Entity Framework is an object-relational mapping framework that can be used to work with data as objects. While you can run the ADO.NET Entity Data Model wizard in Visual Studio to handle generating the Entity Model, this approach, the model-first approach, can put you at a disadvantage if there are changes in your data source or if you want more control over how the entities operate. In this article you will complete the code-first approach to accessing Redshift data using the CData ADO.NET Provider.

1. Open Visual Studio and create a new Windows Form Application. This article uses a C# project with .NET 4.5.
2. Run the command 'Install-Package EntityFramework' in the Package Manger Console in Visual Studio to install the latest release of Entity Framework.

3. Modify the App.config file in the project to add a reference to the Redshift Entity Framework 6 assembly and the connection string.

   To connect to Redshift, set the following:

   • Server: Set this to the host name or IP address of the cluster hosting the Database you want to connect to.
   • Port: Set this to the port of the cluster.
   • Database: Set this to the name of the database. Or, leave this blank to use the default database of the authenticated user.
   • User: Set this to the username you want to use to authenticate to the Server.
   • Password: Set this to the password you want to use to authenticate to the Server.

   You can obtain the Server and Port values in the AWS Management Console:

   1. Open the Amazon Redshift console (http://console.aws.amazon.com/redshift).
   2. On the Clusters page, click the name of the cluster.
   3. On the Configuration tab for the cluster, copy the cluster URL from the connection strings displayed.
   <configuration> ... <connectionStrings> <add name="RedshiftContext" connectionString="Offline=False;User=admin;Password=admin;Database=dev;Server=examplecluster.my.us-west-2.redshift.amazonaws.com;Port=5439;" providerName="System.Data.CData.Redshift" /> </connectionStrings> <entityFramework> <providers> ... <provider invariantName="System.Data.CData.Redshift" type="System.Data.CData.Redshift.RedshiftProviderServices, System.Data.CData.Redshift.Entities.EF6" /> </providers> <entityFramework> </configuration> </code>
4. Add a reference to System.Data.CData.Redshift.Entities.EF6.dll, located in the lib -> 4.0 subfolder in the installation directory.
5. Build the project at this point to ensure everything is working correctly. Once that's done, you can start coding using Entity Framework.
6. Add a new .cs file to the project and add a class to it. This will be your database context, and it will extend the DbContext class. In the example, this class is named RedshiftContext. The following code example overrides the OnModelCreating method to make the following changes:
   • Remove PluralizingTableNameConvention from the ModelBuilder Conventions.
   • Remove requests to the MigrationHistory table.
   using System.Data.Entity; using System.Data.Entity.Infrastructure; using System.Data.Entity.ModelConfiguration.Conventions; class RedshiftContext : DbContext { public RedshiftContext() { } protected override void OnModelCreating(DbModelBuilder modelBuilder) { // To remove the requests to the Migration History table Database.SetInitializer<RedshiftContext>(null); // To remove the plural names modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); } }
7. Create another .cs file and name it after the Redshift entity you are retrieving, for example, Orders. In this file, define both the Entity and the Entity Configuration, which will resemble the example below: using System.Data.Entity.ModelConfiguration; using System.ComponentModel.DataAnnotations.Schema; [System.ComponentModel.DataAnnotations.Schema.Table("Orders")] public class Orders { [System.ComponentModel.DataAnnotations.Key] public System.String ShipName { get; set; } public System.String ShipCity { get; set; } }
8. Now that you have created an entity, add the entity to your context class: public DbSet<Orders> Orders { set; get; }
9. With the context and entity finished, you are now ready to query the data in a separate class. For example: RedshiftContext context = new RedshiftContext(); context.Configuration.UseDatabaseNullSemantics = true; var query = from line in context.Orders select line;