.NET Core 从 appsettings.json 获取连接字符串

Question

我开发了一个简单的 Web 应用程序，将来我想将其作为多租户使用。

所以我想直接把连接字符串写进OnConfiguring方法：

public class ApplicationContext : DbContext
{
    public DbSet<User> Users { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer("connection string from appsettings.json");
        base.OnConfiguring(optionsBuilder);
    }
}

启动class:

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<ApplicationContext>();
    services.AddMvc();
}

如何从 appsettings.json 提取连接字符串到 ApplicationContext class？

我不想为 ApplicationContext class 创建任何构造函数。

Answer 1

假设您有 .NET Core 应用程序并且您的 appsettings.json 文件如下所示：

{
  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Debug",
      "System": "Information",
      "Microsoft": "Information"
    }
  },
  "Production": {
    "SqliteConnectionString": "Filename=./MyDatabase.sqlite"
  }
}

您可以像这样从 Startup.cs 获得 SqliteConnectionString 值：

public void ConfigureServices(IServiceCollection services)
{
    var connection = Configuration["Production:SqliteConnectionString"];

    services.AddDbContext<MyContext>(options =>
        options.UseSqlite(connection)
    );
    ....
 }

然后在您的 DBContext 中，您应该添加接受 DbContextOptions:

的构造函数

public class MyContext : DbContext
{
    public MyContext (DbContextOptions<MyContext> options) : base(options)
    { }

    ...
}

Answer 2

您可以使用工厂模式来解析您的DbContext。

public interface ITenantDbContextFactory
{
    ApplicationContext Create(string tenantId);
}

public class TenantDbContextFactory()
{
    private ApplicationContext context;

    public TenantDbContextFactory()
    {
    }

    public ApplicationContext Create(string tenantId) 
    {
        if(this.context==null) 
        {
            var connectionString = GetConnectionForTenant(tenantId);
            var dbContextBuilder = new DbContextOptionsBuilder();
            dbContextBuilder.UseSqlServer(connectionString);

            this.context = new ApplicationContext(dbContextBuilder);
        }

        return this.context;
    }
}

在启动中：

services.AddDbContext<ApplicationContext>();
services.AddScoped<ITenantDbContextFactory, TenantDbContextFactory>();

您的服务或控制器：

public class HomeController 
{
    private readonly ITenantDbContextFactory dbFactory;
    public HomeControler(ITenantDbContextFactory tenantDbContextFactory)
    {
        this.dbFactory = tenantDbContextFactory;
    }

    public void Action()
    {
        var dbContext = this.dbFactory.Create("tenantA");
        // use your context here
        dbContext...
    }
}

Answer 3

So I want to write the connection string straight into OnConfiguring method:

How can I extract connection string from appsettings.json into ApplicationContext class?

I wouldn't like to create any constructors for ApplicationContext class.

您可以通过 IOptions 使用 选项模式 ，但最简单的方法是在 ApplicationContext 构造函数中使用 DI ;)

请关注以下文章：

Answer 4

.NET 核心 2.0

添加这个 class:

// Requires NuGet package Microsoft.Extensions.Configuration.Json

using Microsoft.Extensions.Configuration;
using System.IO;

namespace RutarBackgroundServices.AppsettingsJson
{
    public static class AppSettingsJson
    {
        public static string ApplicationExeDirectory()
        {
            var location = System.Reflection.Assembly.GetExecutingAssembly().Location;
            var appRoot = Path.GetDirectoryName(location);

            return appRoot;
        }

        public static IConfigurationRoot GetAppSettings()
        {
            string applicationExeDirectory = ApplicationExeDirectory();

            var builder = new ConfigurationBuilder()
            .SetBasePath(applicationExeDirectory)
            .AddJsonFile("appsettings.json");

            return builder.Build();
        }


    }
}

从 "appsettings.json" 文件中获取键 "MssqlConnectionString" 的值：

var appSettingsJson = AppSettingsJson.GetAppSettings();
var connectionString = appSettingsJson["MssqlConnectionString"];

在项目的根目录中创建文件"appsettings.json"：

{
  "MssqlConnectionString": "Server=yourip; Database=yourdbname; User Id=yourusername; Password=yourpassword; Pooling=true;",
  "Db2ConnectionString": "Database=yourdbname;UserID=yourusername;Password=yourpassword;Server=yourip:yourport",
  "SomeOtherKey": "SomeOtherValue"
}

.NET Core 从 appsettings.json 获取连接字符串

.NET Core get connection string from appsettings.json

c#

.net-core

asp.net-core