DDD：将概念显式化 之 验证规约

 刚开始的代码

    class 将概念显式化1
    {
        public void 请假(Guid employeeId, DateTime startDate, DateTime endDate)
        {
            var 剩余天数 = 获取员工可以请假的剩余天数(employeeId);
            var 请假天数 = (endDate - startDate).Days;

            if (请假天数 > 剩余天数)
            {
                //抛出请假异常
            }

            //处理正常的请假逻辑   
        }

        private int 获取员工可以请假的剩余天数(Guid employeeId)
        {
            return 10;
        }
    }

进一步重构

class 将概念显式化2
    {
        public void 请假(Guid employeeId, DateTime startDate, DateTime endDate)
        {
            if (!员工是否满足请假条件(employeeId, startDate, endDate))
            {
                //抛出请假异常
            }

            //处理正常的请假逻辑   
        }

        private bool 员工是否满足请假条件(Guid employeeId, DateTime startDate, DateTime endDate)
        {
            var 剩余天数 = 获取员工可以请假的剩余天数(employeeId);
            var 请假天数 = (endDate - startDate).Days;

            return 请假天数 <= 剩余天数;
        }

        private int 获取员工可以请假的剩余天数(Guid employeeId)
        {
            return 10;
        }
    }

继续重构

    class 将概念显式化3
    {
        public void 请假(员工请假规约 规约)
        {
            if (!规约.是否满足())
            {
                //抛出请假异常
            }

            //处理正常的请假逻辑   
        }
    }

    class 员工请假规约
    {
        private Guid employeeId;
        private DateTime startDate;
        private DateTime endDate;

        public 员工请假规约(Guid employeeId, DateTime startDate, DateTime endDate)
        {
            this.employeeId = employeeId;
            this.startDate = startDate;
            this.endDate = endDate;
        }

        public bool 是否满足()
        {
            var 剩余天数 = 获取员工可以请假的剩余天数(employeeId);
            var 请假天数 = (endDate - startDate).Days;

            return 请假天数 <= 剩余天数;
        }

        private int 获取员工可以请假的剩余天数(Guid employeeId)
        {
            return 10;
        }
    }