Question

我尝试将ASP.Net 5与Entity Framework 7和SQLite一起使用，我发现了一个奇怪的迁移器行为。

我使用Visual Studio 2015并使用模板＆＃34; ASP.NET 5模板Web应用程序＆＃34;创建了一个新项目。

之后我删除了dependecy

"EntityFramework.MicrosoftSqlServer": "7.0.0-rc1-final"

并添加了两个依赖项，而不是名为还原包。

"EntityFramework.Sqlite": "7.0.0-rc1-final",
"Microsoft.Data.Sqlite": "1.0.0-rc1-final"

喜欢那个

"dependencies": {
"EntityFramework.Commands": "7.0.0-rc1-final",
"EntityFramework.Sqlite": "7.0.0-rc1-final",
"Microsoft.Data.Sqlite": "1.0.0-rc1-final",
"Microsoft.AspNet.Authentication.Cookies": "1.0.0-rc1-final",
"Microsoft.AspNet.Diagnostics.Entity": "7.0.0-rc1-final",
"Microsoft.AspNet.Identity.EntityFramework": "3.0.0-rc1-final",
"Microsoft.AspNet.IISPlatformHandler": "1.0.0-rc1-final",
"Microsoft.AspNet.Mvc": "6.0.0-rc1-final",
"Microsoft.AspNet.Mvc.TagHelpers": "6.0.0-rc1-final",
"Microsoft.AspNet.Server.Kestrel": "1.0.0-rc1-final",
"Microsoft.AspNet.StaticFiles": "1.0.0-rc1-final",
"Microsoft.AspNet.Tooling.Razor": "1.0.0-rc1-final",
"Microsoft.Extensions.CodeGenerators.Mvc": "1.0.0-rc1-final",
"Microsoft.Extensions.Configuration.FileProviderExtensions": "1.0.0-rc1-final",
"Microsoft.Extensions.Configuration.Json": "1.0.0-rc1-final",
"Microsoft.Extensions.Configuration.UserSecrets": "1.0.0-rc1-final",
"Microsoft.Extensions.Logging": "1.0.0-rc1-final",
"Microsoft.Extensions.Logging.Console": "1.0.0-rc1-final",
"Microsoft.Extensions.Logging.Debug": "1.0.0-rc1-final",
"Microsoft.VisualStudio.Web.BrowserLink.Loader": "14.0.0-rc1-final"
}

接下来，我转到Startup.cs并更改了像

这样的功能ConfigurationServices

 public void ConfigureServices(IServiceCollection services)
    {
        // Add framework services.
        var dbFilePath =     Path.Combine(PlatformServices.Default.Application.ApplicationBasePath, "test.db");
        services.AddEntityFramework()
         .AddSqlite()
         .AddDbContext<ApplicationDbContext>(options =>
             options.UseSqlite("Filename=" + dbFilePath));
        System.Console.WriteLine("Use DB file:" + dbFilePath);

        services.AddIdentity<ApplicationUser, IdentityRole>()
            .AddEntityFrameworkStores<ApplicationDbContext>()
            .AddDefaultTokenProviders();

        services.AddMvc();

        // Add application services.
        services.AddTransient<IEmailSender, AuthMessageSender>();
        services.AddTransient<ISmsSender, AuthMessageSender>();
        services.AddInstance<IConfigurationRoot>(Configuration);
    }

然后我删除了文件夹＆＃34; Migrations＆＃34;中的所有文件。并构建了解决方案。所有人都已准备好创建迁移。我在项目文件夹上运行git bash并在下一个命令中运行：

blush@BLUSH /d/dev/testMVC
$ dnx ef migrations add firstMigration
Use DB file:D:\dev\testMVC\test.db
Done. To undo this action, use 'ef migrations remove'

和

$ dnx ef database update
Use DB file:D:\dev\testMVC\test.db
Applying migration '20160304130532_firstMigration'.
Done.

好的，我在文件夹＆＃34; Migrations＆＃34;中看到了一个数据库文件和文件。看起来很好。而且我猜想下一次生成的迁移将是空的，而不会更改对象模型。我试着这样做并输入下一个命令：

$ dnx ef migrations add testMigration
Use DB file:D:\dev\testMVC\test.db
Done. To undo this action, use 'ef migrations remove'

我去看了一个生成的迁移类，我看到了这段代码：

 protected override void Up(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.DropForeignKey(name: "FK_IdentityRoleClaim<string>_IdentityRole_RoleId", table: "AspNetRoleClaims");
            migrationBuilder.DropForeignKey(name: "FK_IdentityUserClaim<string>_ApplicationUser_UserId", table: "AspNetUserClaims");
            migrationBuilder.DropForeignKey(name: "FK_IdentityUserLogin<string>_ApplicationUser_UserId", table: "AspNetUserLogins");
            migrationBuilder.DropForeignKey(name: "FK_IdentityUserRole<string>_IdentityRole_RoleId", table: "AspNetUserRoles");
            migrationBuilder.DropForeignKey(name: "FK_IdentityUserRole<string>_ApplicationUser_UserId", table: "AspNetUserRoles");
            migrationBuilder.AddForeignKey(
                name: "FK_IdentityRoleClaim<string>_IdentityRole_RoleId",
                table: "AspNetRoleClaims",
                column: "RoleId",
                principalTable: "AspNetRoles",
                principalColumn: "Id",
                onDelete: ReferentialAction.Cascade);
            migrationBuilder.AddForeignKey(
                name: "FK_IdentityUserClaim<string>_ApplicationUser_UserId",
                table: "AspNetUserClaims",
                column: "UserId",
                principalTable: "AspNetUsers",
                principalColumn: "Id",
                onDelete: ReferentialAction.Cascade);
            migrationBuilder.AddForeignKey(
                name: "FK_IdentityUserLogin<string>_ApplicationUser_UserId",
                table: "AspNetUserLogins",
                column: "UserId",
                principalTable: "AspNetUsers",
                principalColumn: "Id",
                onDelete: ReferentialAction.Cascade);
            migrationBuilder.AddForeignKey(
                name: "FK_IdentityUserRole<string>_IdentityRole_RoleId",
                table: "AspNetUserRoles",
                column: "RoleId",
                principalTable: "AspNetRoles",
                principalColumn: "Id",
                onDelete: ReferentialAction.Cascade);
            migrationBuilder.AddForeignKey(
                name: "FK_IdentityUserRole<string>_ApplicationUser_UserId",
                table: "AspNetUserRoles",
                column: "UserId",
                principalTable: "AspNetUsers",
                principalColumn: "Id",
                onDelete: ReferentialAction.Cascade);
        }

        protected override void Down(MigrationBuilder migrationBuilder)
        {
       ... 
       }

如果我尝试应用此迁移，请捕获下一条错误消息：

$ dnx ef database update
Use DB file:D:\dev\testMVC\test.db
Applying migration '20160304133144_testMigration'.
System.NotSupportedException: SQLite cannot support this migration operation.
   в Microsoft.Data.Entity.Migrations.SqliteMigrationsSqlGenerator.Generate(Drop
ForeignKeyOperation operation, IModel model, RelationalCommandListBuilder builde
r)
   в Microsoft.Data.Entity.Migrations.MigrationsSqlGenerator.<>c.<.cctor>b__50_1
0(MigrationsSqlGenerator g, MigrationOperation o, IModel m, RelationalCommandLis
tBuilder b)
   в Microsoft.Data.Entity.Migrations.MigrationsSqlGenerator.Generate(MigrationO
peration operation, IModel model, RelationalCommandListBuilder builder)
   в Microsoft.Data.Entity.Migrations.MigrationsSqlGenerator.Generate(IReadOnlyL
ist`1 operations, IModel model)
   в Microsoft.Data.Entity.Migrations.SqliteMigrationsSqlGenerator.Generate(IRea
dOnlyList`1 operations, IModel model)
   в Microsoft.Data.Entity.Migrations.Internal.Migrator.GenerateUpSql(Migration
migration)
   в Microsoft.Data.Entity.Migrations.Internal.Migrator.<>c__DisplayClass12_4.<G
etMigrationCommands>b__10()
   в Microsoft.Data.Entity.Migrations.Internal.Migrator.Migrate(String targetMig
ration)
   в Microsoft.Data.Entity.Design.MigrationsOperations.UpdateDatabase(String tar
getMigration, String contextType)
   в Microsoft.Data.Entity.Commands.Program.Executor.<>c__DisplayClass7_0.<Updat
eDatabase>b__0()
   в Microsoft.Data.Entity.Commands.Program.Executor.Execute(Action action)
SQLite cannot support this migration operation.

这是一个问题：我将如何解决这个问题？

Answer 1

这是SQLite的限制。请参阅SQLite Limitations in EF。

这是因为SQLite本身不支持“ADD FOREIGN KEY”。解决此问题的方法是进行表重建。 sqlite.org上的Making Other Kinds Of Table Schema Changes提供了如何构造查询以执行此操作的说明。您很快就会发现SQLite有多乱，以及为什么EF不能为您自动化。

如果您不需要SQLite数据库中的数据，最好只删除它并使用context.Database.EnsureCreated()使用新模型从头开始重建表。

Answer 2

在使用Visual Studio Community 2017 for Mac时我发生了此问题

我发现最简单的方法是删除数据库并重新创建迁移。因为该项目处于开发的早期阶段，所以我当然能够负担得起：

删除数据库文件（app.db）
发出命令dotnet ef migrations remove，直到只有第一次迁移（00000000000000_CreateIdentitySchema）
添加新迁移dotnet ef migrations add CreatedEntities（例如）
更新数据库dotnet ef database update

Answer 3

如果SQLite仅用于内存中的单元测试，请尝试以下操作：

if (context.Database.ProviderName == "Microsoft.EntityFrameworkCore.Sqlite")
{
    context.Database.EnsureCreated();
}
else
{
    context.Database.Migrate();
}

EF7使用SQLite生成错误的迁移

3 个答案: