无法实现 IDbContextFactory 以用于实体框架数据迁移答案

【问题标题】：Unable to implement IDbContextFactory for use with Entity Framework data migrations无法实现 IDbContextFactory 以用于实体框架数据迁移
【发布时间】：2017-08-13 21:47:52
【问题描述】：

尝试如下实现IDbContextFactory。在运行PM 命令时，在return Create(options.ContentRootPath, options.EnvironmentName); 和var optionsBuilder = new DbContextOptionsBuilder<MyProjContext>(); 行出现以下错误

PM> add-migration MyMigration -context MyProjContext

错误

在启动类“Startup”上调用方法“ConfigureServices”时出错。考虑使用 IDbContextFactory 在设计时覆盖 DbContext 的初始化。错误：在程序集“ef，版本=1.0.0.0，文化=中性，PublicKeyToken=adb9793829ddae60”上找不到“UserSecretsIdAttribute”。 System.InvalidOperationException：找不到名为“MyProjContext”的连接字符串。 ....

注意MyProjCnotext.cs和MyProjContextFactory.cs文件都在MyProj\Models文件夹中

MyProjContextFactory 类

public class MyProjContextFactory : IDbContextFactory<MyProjContext>
{
    public MyProjContext Create()
    {
        var environmentName = Environment.GetEnvironmentVariable("Hosting:Environment");
        return Create(Directory.GetCurrentDirectory(), environmentName);
    }

    public MyProjContext Create(DbContextFactoryOptions options)
    {
        return Create(options.ContentRootPath, options.EnvironmentName);
    }

    public MyProjContext Create(string basePath, string environmentName)
    {
        var builder = new ConfigurationBuilder()
            .SetBasePath(basePath)
            .AddJsonFile("appsettings.json")
            .AddJsonFile($"appsettings.{environmentName}.json", true)
            .AddEnvironmentVariables();

        var Configuration = builder.Build();

        var connectionName = nameof(MyProjContext);
        var connectionString = Configuration.GetConnectionString(connectionName);
        if (String.IsNullOrWhiteSpace(connectionString) == true)
            throw new InvalidOperationException($"Could not find a connection string named '{connectionName}'.");

        // init SQL server
        var optionsBuilder = new DbContextOptionsBuilder<MyProjContext>();
        optionsBuilder.UseSqlServer(connectionString);

        return new MyProjContext(optionsBuilder.Options);
    }
}

MyProjContext.cs

namespace MyProj.Models
{
public class MyProjContext : DbContext
{
    public MyProjContext(DbContextOptions<MyProjContext> options) : base(options)
    {

    }
    public DbSet<Table1> Table1 { get; set; }
    public DbSet<Table2> Table2 { get; set; }
    ...
}
}

【问题讨论】：

标签： c# entity-framework entity-framework-migrations

【解决方案1】：

你抛出了一个异常：throw new InvalidOperationException($"Could not find a connection string named '{connectionName}'.");

添加appsettings.json和appsettings.Development.json：

{
    ...
    "ConnectionStrings": {
        "MyProjContext": "..."
    }
}

【讨论】：