1.配置DbContext

1.1.Startup / ConfigureServices

services.AddDbContext<CustDbContext>(options => options.UseSqlServer(configuration["ConnectionStrings:DefaultConnection"]));

如果不能注入Configuration，则为：

//读取配置文件
IConfiguration configuration = new ConfigurationBuilder().AddJsonFile("appsettings.json", false, true).Build();
services.AddSingleton(configuration);
services.AddDbContext<CustDbContext>(options => options.UseSqlServer(configuration["ConnectionStrings:DefaultConnection"]));

1.2.CustDbContext

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!optionsBuilder.IsConfigured)
            {
                optionsBuilder.UseSqlServer("Name=ConnectionStrings:DefaultConnection");
            }
        }

2.注入DbContext

2.1.通过 IServiceProvider 注入

provider.GetService<CustDbContext>()

2.2.构造函数注入

    public class CustClass
    {
        private readonly CustDbContext dbContext;
        public CustClass(CustDbContext _dbContext)
        {
            dbContext = _dbContext;
        }
    }