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Access Google Cloud Storage Data with Entity Framework 6

This article shows how to access Google Cloud Storage 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 Google Cloud Storage 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 Google Cloud Storage Entity Framework 6 assembly and the connection string.

    Authenticate with a User Account

    You can connect without setting any connection properties for your user credentials. After setting InitiateOAuth to GETANDREFRESH, you are ready to connect.

    When you connect, the Google Cloud Storage OAuth endpoint opens in your default browser. Log in and grant permissions, then the OAuth process completes

    Authenticate with a Service Account

    Service accounts have silent authentication, without user authentication in the browser. You can also use a service account to delegate enterprise-wide access scopes.

    You need to create an OAuth application in this flow. See the Help documentation for more information. After setting the following connection properties, you are ready to connect:

    • InitiateOAuth: Set this to GETANDREFRESH.
    • OAuthJWTCertType: Set this to "PFXFILE".
    • OAuthJWTCert: Set this to the path to the .p12 file you generated.
    • OAuthJWTCertPassword: Set this to the password of the .p12 file.
    • OAuthJWTCertSubject: Set this to "*" to pick the first certificate in the certificate store.
    • OAuthJWTIssuer: In the service accounts section, click Manage Service Accounts and set this field to the email address displayed in the service account Id field.
    • OAuthJWTSubject: Set this to your enterprise Id if your subject type is set to "enterprise" or your app user Id if your subject type is set to "user".
    • ProjectId: Set this to the Id of the project you want to connect to.

    The OAuth flow for a service account then completes.

    <configuration> ... <connectionStrings> <add name="GoogleCloudStorageContext" connectionString="Offline=False;ProjectId='project1';InitiateOAuth=GETANDREFRESH" providerName="System.Data.CData.GoogleCloudStorage" /> </connectionStrings> <entityFramework> <providers> ... <provider invariantName="System.Data.CData.GoogleCloudStorage" type="System.Data.CData.GoogleCloudStorage.GoogleCloudStorageProviderServices, System.Data.CData.GoogleCloudStorage.Entities.EF6" /> </providers> <entityFramework> </configuration> </code>
  4. Add a reference to System.Data.CData.GoogleCloudStorage.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 GoogleCloudStorageContext. 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 GoogleCloudStorageContext : DbContext { public GoogleCloudStorageContext() { } protected override void OnModelCreating(DbModelBuilder modelBuilder) { // To remove the requests to the Migration History table Database.SetInitializer<GoogleCloudStorageContext>(null); // To remove the plural names modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); } }
  7. Create another .cs file and name it after the Google Cloud Storage entity you are retrieving, for example, Buckets. 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("Buckets")] public class Buckets { [System.ComponentModel.DataAnnotations.Key] public System.String Name { get; set; } public System.String OwnerId { get; set; } }
  8. Now that you have created an entity, add the entity to your context class: public DbSet<Buckets> Buckets { set; get; }
  9. With the context and entity finished, you are now ready to query the data in a separate class. For example: GoogleCloudStorageContext context = new GoogleCloudStorageContext(); context.Configuration.UseDatabaseNullSemantics = true; var query = from line in context.Buckets select line;