Question

仅仅是为了测试，我不想从StartUp.cs文件中进行依赖注入。如何从EF Core DBContext获取IHostingEnvironment。

我采用一个带有空模板的新asp.net核心项目。我已经创建了一个dbcontext，如下所示。我想用Environment.ContentRootPath而不是Directory.GetCurrentDirectory（）。但是我不想从Startup.cs做任何注入。

public class MyDBContext: DbContext
{

    public IConfigurationRoot Configuration { get; set; }
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        var builder = new ConfigurationBuilder()
              .SetBasePath(Path.Combine(Directory.GetCurrentDirectory(), "..\\..\\.."))
              .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
        Configuration = builder.Build();
        optionsBuilder.UseSqlServer(Configuration.GetConnectionString("SQLCN"));// @"Server=(localdb)\mssqllocaldb;Database=MyDatabase;Trusted_Connection=True;");
    }

    public DbSet<Teacher> Teachers { get; set; }
    public DbSet<Lesson> Lessons { get; set; }
}

如果我在dbcontext构造函数中添加IHostingEnvironment，如下所示

public class MyDBContext: DbContext
{
    private readonly IHostingEnvironment env;
    public MyDBContext(IHostingEnvironment env) : base()
    {
        this.env = env;
    }


    public IConfigurationRoot Configuration { get; set; }
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        var builder = new ConfigurationBuilder()
              .SetBasePath(this.env.ContentRootPath)
              .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
        Configuration = builder.Build();
        optionsBuilder.UseSqlServer(Configuration.GetConnectionString("SQLCN"));// @"Server=(localdb)\mssqllocaldb;Database=MyDatabase;Trusted_Connection=True;");
    }

    public DbSet<Teacher> Teachers { get; set; }
    public DbSet<Lesson> Lessons { get; set; }
}

从Package-Manager控制台添加迁移时出现以下错误。

PM> Add-Migration InitMyDBContext

在'MyDBContext'上找不到无参数构造函数。要么添加一个无参数构造函数到'MyDBContext'或添加一个实现 'IDbContextFactory'在同一个程序集中 'MyDBContext'。

Answer 1

您应该能够将IHostingEnvironment直接注入DbContext的构造函数。

public class MyDBContext: DbContext {
    private readonly IHostingEnvironment env;
    public MyDBContext(IHostingEnvironment env) : base() {
        this.env = env;
    }

    public IConfigurationRoot Configuration { get; set; }
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) {
        var builder = new ConfigurationBuilder()
            .SetBasePath(env.ContentRootPath)
            .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
        Configuration = builder.Build();
        optionsBuilder.UseSqlServer(Configuration.GetConnectionString("SQLCN"));// @"Server=(localdb)\mssqllocaldb;Database=MyDatabase;Trusted_Connection=True;");
    }

    public DbSet<Teacher> Teachers { get; set; }
    public DbSet<Lesson> Lessons { get; set; }
}

框架已经知道了界面。

您可以照常添加上下文。减号配置，因为您表示不想在Startup

中执行此操作

services.AddDbContext<MyDBContext>();

初始化上下文时，框架应根据构造函数参数的存在将IHostingEnvironment的实现注入上下文。

如何从ASP.NET Core中的DbContext获取IHostingEnvironment

1 个答案: