EF 的霸气配置，秒杀一切

class Program
    {
        static void Main(string[] args)
        {
            TestContext testContext = new TestContext();
            ///获取数据库表Person中的所有数据 在查询的时候最好加上AsNoTracking 禁止EF跟踪
          //  var personList = testContext.Persons.AsNoTracking().ToList();
        }
    }

    public class TestContext : DbContext
    {
        private static TestContext _instance;

        public static TestContext Instance
        {
            get
            {
                if (_instance == null)
                {
                    _instance = new TestContext();
                }
                return _instance;
            }
        }

        private string _connectionString;

        public string ConnectionString
        {
            get
            {
                if (string.IsNullOrWhiteSpace(_connectionString))
                {
                    _connectionString = ConfigurationManager.ConnectionStrings["testConn"].ConnectionString;
                }
                return _connectionString;
            }
            set
            {
                _connectionString = value;
            }
        }

        public TestContext()
            : base("name=testConn")
        {
            _connectionString = ConfigurationManager.ConnectionStrings["testConn"].ConnectionString;
        }
        public TestContext(string connectionString)
            : base(connectionString)
        {

        }
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            ///DomainMapping  所在的程序集一定要写对，因为目前在当前项目所以是采用的当前正在运行的程序集 如果你的mapping在单独的项目中 记得要加载对应的assembly
            ///这是重点
            var typesToRegister = Assembly.GetExecutingAssembly().GetTypes()
          .Where(type => !String.IsNullOrEmpty(type.Namespace))
          .Where(type => type.BaseType != null && type.BaseType.BaseType != null && type.BaseType.BaseType.GetGenericTypeDefinition() == typeof(EntityTypeConfiguration<>));
            foreach (var type in typesToRegister)
            {
                dynamic configurationInstance = Activator.CreateInstance(type);
                modelBuilder.Configurations.Add(configurationInstance);
            }

            base.OnModelCreating(modelBuilder);
        }

 
    }

    public class BaseDomain
    {

    }
    [Table("Person")]
    public class Person
    {
        public string ID { get; set; }
        public string Name { get; set; }

        public string Age { get; set; }
    }

    public class PersonMapping : BaseDomainMapping<Person>
    {
        public override void Init()
        {
            this.ToTable("Person");
            this.HasKey(l => l.ID);
            this.Property(l => l.Name).HasMaxLength(200).IsRequired();//设置Name属性长度为200 并且是必填
            this.Property(l => l.Age).HasMaxLength(200).IsOptional(); //设置Age长度为200 并且可为空
        }
    }


    public abstract class BaseDomainMapping<T> : EntityTypeConfiguration<T>
       where T : BaseDomain, new()
    {

        public BaseDomainMapping()
        {
            Init();
        }
        /// <summary>
        /// 初始化代码
        /// </summary>
        public virtual void Init()
        {
            Console.WriteLine("Init");
        }
    }