使用带有 Azure Functions 的 EntityFrameworkCore 迁移的 DbContext 问题

Question

我有一个多项目解决方案，包括数据层和 Azure Functions 层。我在添加 entity framework 迁移时遇到问题。我收到一条错误消息，指出我的 DbContext 需要一个无参数构造函数。使用 WebApi 时我不需要这个，但自从切换到 Azure Function 后，我收到了这个错误。我怀疑这与 Functions 项目中的 Startup 配置有关，但我似乎无法找到一种方法来获取它。

在数据层我有一个 DbContext:

public class SampleContext : IdentityDbContext<User>, IDbContext
{

    public SampleContext(DbContextOptions options) : base(options)
    {

    }
}

我的函数应用有一个启动项class：

public class Startup : FunctionsStartup
{

    public override void Configure(IFunctionsHostBuilder builder)
    {
        var configurationConnectionString = Environment.GetEnvironmentVariable("ConnectionString");
        var localRoot = Environment.GetEnvironmentVariable("AzureWebJobsScriptRoot");
        var azureRoot = $"{Environment.GetEnvironmentVariable("Home")}/site/wwwroot";
        var actualRoot = localRoot ?? azureRoot;


        var config = new ConfigurationBuilder()
                .SetBasePath(actualRoot)
                .AddJsonFile("local.settings.json", optional: true, reloadOnChange: true)
                .AddEnvironmentVariables()
                .AddAzureAppConfiguration(options =>
                    {
                        options.Connect(configurationConnectionString)
                            .ConfigureKeyVault(kv =>
                            {
                                kv.SetCredential(new DefaultAzureCredential());
                            });
                    })
                .Build();

        ...

        IServiceCollection services = builder.Services;

        services.AddSingleton(config);

        string connectionString = config["DefaultConnection"];


        services.AddDbContext<SampleContext>(options =>
            SqlServerDbContextOptionsExtensions.UseSqlServer(options, connectionString)
         );

        ...

     }

}

我正在使用代码优先，当我尝试创建迁移时

   add-migration initial -c SampleContext -p sample.data -s sample.functions -v

我收到这个错误：

Using assembly 'Sample.Data'.
Using startup assembly 'Sample.Functions'.
Using application base 'F:\GitHub\Sample\Sample.Functions\bin\Debug\netcoreapp3.1'.
Using working directory 'F:\GitHub\Sample\Sample.Functions'.
Using root namespace 'Sample.Data'.
Using project directory 'F:\GitHub\Sample\Sample\Sample.Data\'.
Finding DbContext classes...
Finding IDesignTimeDbContextFactory implementations...
Finding application service provider...
Finding Microsoft.Extensions.Hosting service provider...
No static method 'CreateHostBuilder(string[])' was found on class 'Program'.
No application service provider was found.
Finding DbContext classes in the project...
Found DbContext 'SampleContext'.
Microsoft.EntityFrameworkCore.Design.OperationException: Unable to create an object of type 'SampleContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728
 ---> System.MissingMethodException: No parameterless constructor defined for type 'Sample.Data.Infrastructure.SampleContext'.
   at System.RuntimeType.CreateInstanceDefaultCtorSlow(Boolean publicOnly, Boolean wrapExceptions, Boolean fillCache)
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, Boolean wrapExceptions)
   at System.Activator.CreateInstance(Type type, Boolean nonPublic, Boolean wrapExceptions)

谁能帮我解决这个问题？

Answer 1

这就是我的工作方式：

public void ConfigureServices(IFunctionsHostBuilder builder, IConfigurationRoot config)
{
    IServiceCollection services = builder.Services;

    services.AddSingleton(config);
    services.AddApplicationInsightsTelemetry();

    string connectionString = config.GetConnectionString("MyConnectionString");
    services.AddDbContext<MyDbContext>(
        options => SqlServerDbContextOptionsExtensions.UseSqlServer(options, connectionString)
        );

    services.RegisterServiceLayer();
}

使用带有 Azure Functions 的 EntityFrameworkCore 迁移的 DbContext 问题

Issue with DbContext using EntityFrameworkCore Migrations with Azure Functions

c#

entity-framework-core

azure-functions

entity-framework-migrations