如何将连接字符串从appsettings。[name] .json传递到.NET Core中的DbContext？ [英] How to pass connection string from appsettings.[name].json to DbContext in .NET Core?

问题描述

我有一个.net核心应用程序。我将连接字符串写入appsettings.json文件中。
但是，现在，我想为我的上下文获取该连接字符串。

I have a .net core app. I write my connection string in appsettings.json file. But, now, I want to get that connection string for my context. How to do that?

在.net framework 4.6中，我使用了以下方法：

In .net framework 4.6 I used this:

ConfigurationManager.ConnectionStrings["ConnStrName"].ConnectionString;

我有appsettings.Development.json像这样（***可以是任何名称）：

I have appsettings.Development.json like this (*** could be any name):

"ConnectionStrings": {
    "***": "Server=***;Database=****;Trusted_Connection=True;MultipleActiveResultSets=true;"
  }

我添加了服务：

services.AddTransient<MyContext>(provider =>
            {
                return new MyContext(configuration["ConnectionStrings:***"]);
            });

这是上下文构造函数（仅此，不是默认的，因为如果我编写默认的，则不会） t从json文件中获取我的连接字符串）：

and this is context constructor (ONLY THIS, not default ones because if I write a default one doesn't take my connection string from json file):

public MyContext(string connectionString)
        : base(connectionString)
    {
        try
        {
            this.Database.Log = (s) => System.Diagnostics.Debug.Write(s);
        }
        catch (Exception e)
        {
            //CurrentLogger.Log.Error(e);
        }
    }

之后，在运行后出现此错误Enable-Migration命令

After that I've got this error after I run Enable-Migration command

目标上下文 MyContext不可构造。添加默认的构造函数或提供IDbContextFactory的实现。

如果我能以某种方式从json中获取连接字符串，则可以：

If somehow I could get connection string from json here:

一切都会很好。但是，如果可能的话，我想在 .NET CORE 中使用一行来做到这一点，例如在.net框架中：

all will be good. But I want to do that with a single line in .NET CORE if it would be possible, like in .net framework: with this:

ConfigurationManager.ConnectionStrings["ConnStrName"].ConnectionString;

.net framework 4.6

推荐答案

.NET Core中的所有内容都是基于依赖注入，而不是使用诸如ConfigurationManager之类的静态实例。

Everything in .NET Core is built around dependency injection instead of using static instances of things like ConfigurationManager.

您可以用几种不同的方法来做到这一点。

You could do this in a couple different ways.

首先将使用以下方法在Startup.cs ConfigureServices中注册DbContext：

First would be registering your DbContext in Startup.cs ConfigureServices using something like this:

services.AddDbContext<MyContext>(context => context.UseSqlServer(Configuration.GetConnectionString("name")));

然后，当您的存储库/服务/任何类需要使用Context时，它将注入到

Then when your repository/service/whatever class needs to use the Context, it will be injected into the class using the constructor so you can use it.

public class SomeClass(MyContext context)
{

}

或者，如果您不想那样做，可以还将 IConfiguration注入到DbContext的构造函数中，然后使用IConfiguration来获取连接字符串：

Or, if you don't want to do it that way, you can also inject 'IConfiguration' into the constructor of your DbContext and then do use the IConfiguration to get the connection string:

public class SomeClass(IConfiguration config)
{
    config.GetConnectionString("name")
}

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