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Access REST Data with Entity Framework 6

This article shows how to access REST data using an Entity Framework code-first approach. Entity Framework 6 is available in .NET 4.5 and above.

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 REST 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 REST Entity Framework 6 assembly and the connection string.

    See the Getting Started chapter in the data provider documentation to authenticate to your data source: The data provider models REST APIs as bidirectional database tables and XML/JSON files as read-only views (local files, files stored on popular cloud services, and FTP servers). The major authentication schemes are supported, including HTTP Basic, Digest, NTLM, OAuth, and FTP. See the Getting Started chapter in the data provider documentation for authentication guides.

    After setting the URI and providing any authentication values, set Format to "XML" or "JSON" and set DataModel to more closely match the data representation to the structure of your data.

    The DataModel property is the controlling property over how your data is represented into tables and toggles the following basic configurations.

    • Document (default): Model a top-level, document view of your REST data. The data provider returns nested elements as aggregates of data.
    • FlattenedDocuments: Implicitly join nested documents and their parents into a single table.
    • Relational: Return individual, related tables from hierarchical data. The tables contain a primary key and a foreign key that links to the parent document.

    See the Modeling REST Data chapter for more information on configuring the relational representation. You will also find the sample data used in the following examples. The data includes entries for people, the cars they own, and various maintenance services performed on those cars.

    <configuration> ... <connectionStrings> <add name="RESTContext" connectionString="Offline=False;DataModel=Relational;URI=C:\people.xml;Format=XML;" providerName="System.Data.CData.REST" /> </connectionStrings> <entityFramework> <providers> ... <provider invariantName="System.Data.CData.REST" type="System.Data.CData.REST.RESTProviderServices, System.Data.CData.REST.Entities.EF6" /> </providers> <entityFramework> </configuration> </code>
  4. Add a reference to System.Data.CData.REST.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 RESTContext. 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 RESTContext : DbContext { public RESTContext() { } protected override void OnModelCreating(DbModelBuilder modelBuilder) { // To remove the requests to the Migration History table Database.SetInitializer<RESTContext>(null); // To remove the plural names modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); } }
  7. Create another .cs file and name it after the REST entity you are retrieving, for example, people. 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("people")] public class people { [System.ComponentModel.DataAnnotations.Key] public System.String [ personal.name.first ] { get; set; } public System.String [ personal.name.last ] { get; set; } }
  8. Now that you have created an entity, add the entity to your context class: public DbSet<people> people { set; get; }
  9. With the context and entity finished, you are now ready to query the data in a separate class. For example: RESTContext context = new RESTContext(); context.Configuration.UseDatabaseNullSemantics = true; var query = from line in context.people select line;