asp.netCore連接多個數據庫

1.首先要有對應的context實體類,

多個實體類的構造函數的參數都應該是集合

 public class firstContext : DbContext
    {
        //多個數據庫應該使用這個構造函數，參數是上下文的集合
        public GalpOnlineContext(DbContextOptions<firstContext> options) : base(options)
        {

        }

        //自定義DbContext實體屬性名與數據庫表對應名稱（默認 表名與屬性名對應是 User與Users）
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<User>().ToTable("user");
            modelBuilder.Entity<Project>().ToTable("project");
            //相關表名稱的和類的對應
            base.OnModelCreating(modelBuilder);
        }


        public DbSet<User> User { get; set; }
      //....

        //第二種方法，重載父級的構造函數，和配置，這個只能是一個數據庫時候的構造函數
        /* 
        public firstContext(DbContextOptions options) : base(options)
        {
            // Using the default constructor
        }*/

    }
}    

　2.在appsettings.json中進行配置數據庫連接的信息

{
  "Logging": {
    "LogLevel": {
      "Default": "Warning"
    }
  },
  "ConnectionStrings": {
    "firstContext": "Server=localhost;database=test;uid=root;pwd=123456;sslmode=none",
    "secondContext": "Server=localhost;database=test2;uid=root;pwd=123456;sslmode=none"
  },

　3.在startup.cs文件中注冊數據庫上下文的信息

  public void ConfigureServices(IServiceCollection services)
        {
            services.Configure<CookiePolicyOptions>(options =>
            {
                //  options.CheckConsentNeeded = context => false;實現session,默認是true
                options.CheckConsentNeeded = context => false;  
                options.MinimumSameSitePolicy = SameSiteMode.None;
            });

            //注冊數據庫的服務
            string connectionString = Configuration.GetConnectionString("firstContext");
            string connectionString2 = Configuration.GetConnectionString("secondContext");

            services.AddDbContext<firstContext>(options => options.UseMySql(connectionString));
            services.AddDbContext<secondContext>(options => options.UseMySql(connectionString2));


            //注冊session
            services.AddDistributedMemoryCache();
            services.AddSession(Options =>
          {
              Options.IdleTimeout = TimeSpan.FromSeconds(1000);
              Options.Cookie.HttpOnly = true;
          });
            //services.AddMemoryCache();//使用本地緩存必須添加

            //注冊mvc服務
            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

        }

　　然后就可以了，在使用的地方引入上下文就可以了

 public class TestController : Controller
    {
        public readonly firstContext _context;
        //構造函數，依賴注入數據庫上下文就可以了
        public TestController(firstContext context)
        {
            _context = context;
        }
        public ActionResult Index(string page)
        {
            List<Project> projects = _context.Project.ToList();
            ViewBag.projects = projects;
            return View();
        }
    }