C# 值不能为null。参数名称connectionString

大家好，我在将数据保存到数据库时遇到问题。我正在使用

EF

和

.netcore

。我已经在下面提供了我的示例代码：

这里到底出了什么问题？我在

ConfigureServices

中为MyContext提供了

services.AddDbContext

public class MyContext: DbContext
{
    private IConfigurationRoot _config;

    public MyContext(IConfigurationRoot config)
    {
       this._config = config;
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        base.OnConfiguring(optionsBuilder);
        optionsBuilder.UseSqlServer(_config["Data:ConnectionString"]);
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        ...
    }
}

appsettings.json

{
  "Data": {
    "ConnectionString": "Data Source=MyDataSource;Initial Catalog=MyCatalog;Trusted_Connection=True"},

另一类：

public class AnotherClass
{ 
     private MyContext mycontext;
     private IConfigurationRoot configurationRoot;

     public AnotherClass()
     { 
        var builder = new ConfigurationBuilder();
        configurationRoot = builder.Build();
        mycontext = new MyContext(configurationRoot);
     }

     public MyMethod()
     {
        try
        {
            //object to be saved using EF
            var saveObj = new SaveObj()
            {
             //pretend to have initialize some object here to save
            };

            mycontext.SaveObj.Add(saveObj);
            mycontext.SaveChanges();
        }
        catch(Exception e)
        {
           //Throws an exception. Value cannot be null. Parameter name: connectionString
        }
    }
}

看看这个：

我认为您的appsettings.json应该如下所示：

{
  "ConnectionStrings": {
    "DefaultConnection": "Data Source=MyDataSource;Initial Catalog=MyCatalog;Trusted_Connection=True"
  }
}

跳过“数据”部分