如何在另一个项目的上下文中读取 appsettings.json ？ ASP.NET核心

我需要使用相同的ConnectionString在两个地方。在我的网络项目中Insig.Api其中包含ConnectionString from appsettings.json并在另一个项目类库中Insing.Infrastructure我的数据库上下文在哪里。

Insig.Api-Startup.cs

public class Startup
    {
        public IConfiguration Configuration { get; }

        public Startup(IHostingEnvironment env)
        {
            var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
                .AddEnvironmentVariables();
            Configuration = builder.Build();
        }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc();

            services.AddSingleton(Configuration);
            services.AddDbContext<InsigContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
        }
    }

Insig.基础设施-InsigContext.cs

public class InsigContext : DbContext, IDesignTimeDbContextFactory<InsigContext>
{
    public InsigContext() { }

    public InsigContext(DbContextOptions<InsigContext> options) : base(options) { }

    public DbSet<Sample> Samples { get; set; }

    public InsigContext CreateDbContext(string[] args)
    {    
        var builder = new DbContextOptionsBuilder<InsigContext>();    

        builder.UseSqlServer("Data Source=.\\SQLEXPRESS;Initial Catalog=InsigDB;Integrated Security=True;MultipleActiveResultSets=True");
   // Here I would like to use ConnectionString instead of raw string.    

        return new InsigContext(builder.Options);
    }
}

如你看到的ConnectionString由于迁移（来自代码优先方法），上下文中也需要它。

编辑-下面的代码不起作用。当我试图Add-Migration Init然后我收到一个错误：Value cannot be null. Parameter name: connectionString

public class InsigContext : DbContext
    {
        private readonly string _connectionString;    

        public InsigContext(DbContextOptions<InsigContext> options, IConfiguration configuration) : base(options)
        {
            _connectionString = configuration.GetSection("ConnectionStrings:DefaultConnection").Value;
        }

        public InsigContext() { }

        public DbSet<Sample> Samples { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!optionsBuilder.IsConfigured)
            {
                optionsBuilder.UseSqlServer(_connectionString);
            }
        }
    }

你可以注射IConfiguration给你的InsigContext构造函数并使用它来获取连接字符串

private readonly string connectionString;
public InsigContext(DbContextOptions<InsigContext> options,IConfiguration configuration)
                                                                          : base(options)
{ 
   this.connectionString = configuration.GetSection("ConnectionStrings:DefaultConnection")
                                     .Value;
}
// you can use this.connectionString now

IConfiguration定义于Microsoft.Extensions.Configuration命名空间。因此，您可能想在类库中添加对此的引用。

如果您想访问IConfiguration对象在另一个方法中，创建一个局部变量并在构造函数中设置它

private readonly IConfiguration configuration;
public InsigContext(IConfiguration configuration)
{
    this.configuration = configuration;
}

public void CreateDbContext(string[] args)
{
   // you can use this.configuration here as needed or get conn string
}

不需要多个构造函数。在您要注入所需依赖项的位置保留一个构造函数。