c# Azure Mobile Apps - 添加新模型不起作用

Question

我创建了一个 Azure 移动应用程序，然后下载了生成的后端和移动应用程序。当我启动它时，它成功获取数据库中的 2 个待办事项。但是，一旦我添加如下用户模型 - 它就会停止在移动应用程序中获取待办事项。我不知道是什么导致了冲突。

• 如果我删除用户模型和引用，我可以再次在移动应用上检索待办事项

当我从 DBcontext 中注释掉这一行时，它再次起作用:

//public DbSet<User> Users { get; set; }

启动:

public partial class Startup
    {
        public static void ConfigureMobileApp(IAppBuilder app)
        {
            HttpConfiguration config = new HttpConfiguration();

            //For more information on Web API tracing, see http://go.microsoft.com/fwlink/?LinkId=620686 
            config.EnableSystemDiagnosticsTracing();

            new MobileAppConfiguration()
                .UseDefaultConfiguration()
                .ApplyTo(config);

            // Map routes by attribute
            config.MapHttpAttributeRoutes();

            // Use Entity Framework Code First to create database tables based on your DbContext
            Database.SetInitializer(new AuthApp231Initializer());

            // To prevent Entity Framework from modifying your database schema, use a null database initializer
            // Database.SetInitializer<AuthApp231Context>(null);

            MobileAppSettingsDictionary settings = config.GetMobileAppSettingsProvider().GetMobileAppSettings();

            if (string.IsNullOrEmpty(settings.HostName))
            {
                // This middleware is intended to be used locally for debugging. By default, HostName will
                // only have a value when running in an App Service application.
                app.UseAppServiceAuthentication(new AppServiceAuthenticationOptions
                {
                    SigningKey = ConfigurationManager.AppSettings["SigningKey"],
                    ValidAudiences = new[] { ConfigurationManager.AppSettings["ValidAudience"] },
                    ValidIssuers = new[] { ConfigurationManager.AppSettings["ValidIssuer"] },
                    TokenHandler = config.GetAppServiceTokenHandler()
                });
            }
            app.UseWebApi(config);
        }
    }

    public class AuthApp231Initializer : CreateDatabaseIfNotExists<AuthApp231Context>
    {
        protected override void Seed(AuthApp231Context context)
        {
            List<TodoItem> todoItems = new List<TodoItem>
            {
                new TodoItem { Id = Guid.NewGuid().ToString(), Text = "First item", Complete = false },
                new TodoItem { Id = Guid.NewGuid().ToString(), Text = "Second item", Complete = false },
            };

            foreach (TodoItem todoItem in todoItems)
            {
                context.Set<TodoItem>().Add(todoItem);
            }

            /*List<User> users = new List<User>
            {
                new User { Id = Guid.NewGuid().ToString(), Username = "adrian", Password = "supersecret" }
            };

            foreach (User user in users)
            {
                context.Set<User>().Add(user);
            }*/

            base.Seed(context);
        }
    }

数据对象:

public class User :EntityData
    {

        public string Username { get; set; }

        public string Password { get; set; }
    }

上下文:

public class AuthApp231Context : DbContext
    {
        // You can add custom code to this file. Changes will not be overwritten.
        // 
        // If you want Entity Framework to alter your database
        // automatically whenever you change your model schema, please use data migrations.
        // For more information refer to the documentation:
        // http://msdn.microsoft.com/en-us/data/jj591621.aspx

        private const string connectionStringName = "Name=MS_TableConnectionString";

        public AuthApp231Context() : base(connectionStringName)
        {
        } 

        public DbSet<TodoItem> TodoItems { get; set; }
        public DbSet<User> Users { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Conventions.Add(
                new AttributeToColumnAnnotationConvention<TableColumnAttribute, string>(
                    "ServiceTableColumn", (property, attributes) => attributes.Single().ColumnType.ToString()));
        }
    }

Answer 1

据我所知，示例移动应用后端项目仅包含 TodoItem 模型，当您运行项目时，Database.SetInitializer(new AuthApp231Initializer()) 当数据库不存在时，将被触发并创建数据库和TodoItem表。如果在数据库初始化后添加其他数据模型，则需要迁移数据库。

注意:您可以利用 Add-Migration 添加自定义迁移，并使用 Update-Database 使数据库保持最新状态。此外，您还可以利用 MigrateDatabaseToLatestVersion 初始化程序自动升级数据库。

更多关于如何启用EF Code First迁移的详细信息，您可以引用这个官方tutorial .