Access Google BigQuery Data with Entity Framework 6
Tags: csharp, sql, bigquery, tutorial
Published: 2020-01-31 22:01:12

The Microsoft 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 BigQuery 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 BigQuery Entity Framework 6 assembly and the connection string.

    Google uses the OAuth authentication standard. To access Google APIs on behalf of individual users, you can use the embedded credentials or you can register your own OAuth app.

    OAuth also enables you to use a service account to connect on behalf of users in a Google Apps domain. To authenticate with a service account, you will need to register an application to obtain the OAuth JWT values.

    In addition to the OAuth values, you will need to specify the DatasetId and ProjectId. See the "Getting Started" chapter of the CData Help documentation for a guide to using OAuth.

    ```xml
    <configuration>
       ... 
      <connectionStrings>
        <add name="GoogleBigQueryContext" connectionString="Offline=False;DataSetId=MyDataSetId;ProjectId=MyProjectId;InitiateOAuth=GETANDREFRESH" providerName="System.Data.CData.GoogleBigQuery" />
      </connectionStrings>
      <entityFramework>
        <providers>
           ... 
          <provider invariantName="System.Data.CData.GoogleBigQuery" type="System.Data.CData.GoogleBigQuery.GoogleBigQueryProviderServices, System.Data.CData.GoogleBigQuery.Entities.EF6" />
        </providers>
      <entityFramework>
    </configuration>
    </code> 
    ```

4. Add a reference to System.Data.CData.GoogleBigQuery.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 `GoogleBigQueryContext`. 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.

    ```csharp
    using System.Data.Entity;
    using System.Data.Entity.Infrastructure;
    using System.Data.Entity.ModelConfiguration.Conventions;
    
    class GoogleBigQueryContext : DbContext {
      public GoogleBigQueryContext() { }
    
      protected override void OnModelCreating(DbModelBuilder modelBuilder)
      {
        // To remove the requests to the Migration History table
        Database.SetInitializer<GoogleBigQueryContext>(null);  
        // To remove the plural names    
        modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
      }  
    }
    ```

7. Create another .cs file and name it after the BigQuery entity you are retrieving, for example, Orders. In this file, define both the Entity and the Entity Configuration, which will resemble the example below:

    ```csharp
    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 OrderName { get; set; }
      public System.String Freight { get; set; }
    }
    ```
 
8. Now that you have created an entity, add the entity to your context class:

    ```csharp
    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:

    ```csharp
    GoogleBigQueryContext context = new GoogleBigQueryContext();
    context.Configuration.UseDatabaseNullSemantics = true;
    var query = from line in context.Orders select line;
    ```