贫血模型和充血模型

贫血模型

贫血模型,是指Model中,仅包含状态(属性),不包含行为(方法),采用这种设计时,需要分离出DB层,专门用于数据库操作.

充血模型

充血模型,是指Model中既包括状态,又包括行为,是最符合面向对象的设计方式

举例说明

对于员工Employee来说,每个员工的属性有id,Name,Sex,BirthDay,Parent(上级),行为有查找,保存,删除,职位调整(更换上级)等

采用贫血模型实现

Model层

public class Employee
{
    public string Id { get; set; }
    public string Name { get; set; }
    public string Sex { get; set; }
    public DateTime? BirthDay { get; set; }
    /// <summary>
    /// 直属上级的Id
    /// </summary>
    public string ParentId { get; set; }
}

DB层

//实现方法略    
public class EmpDAO
{
    public static bool AddEmployee(Employee emp);
    public static bool UpdateEmployee(Employee emp);
    public static bool DeleteEmployee(Employee emp);
    public static Employee GetEmployeeById(string Id);
}

BLL层

public class EmpBLL
{
    public void Test()
    {
        Employee emp1 = new Employee() { Id = System.Guid.NewGuid().ToString(), Name = "张三", Sex = "男" };
        Employee emp2 = new Employee() { Id = System.Guid.NewGuid().ToString(), Name = "李四", Sex = "男", ParentId = emp1.Id };
        //插入员工
        EmpDAO.AddEmployee(emp1);
        EmpDAO.AddEmployee(emp2);

        //取员工的上级
        var emp2Parent = EmpDAO.GetEmployeeById(emp2.ParentId);
        var emp2Parent_Parent = EmpDAO.GetEmployeeById(emp2Parent.ParentId);

        //删除员工
        EmpDAO.DeleteEmployee(emp1);
        EmpDAO.DeleteEmployee(emp2);
    }
}

采用充血模型实现

Model层

public class Employee
{
    public string Id { get; set; }
    public string Name { get; set; }
    public string Sex { get; set; }
    public DateTime? BirthDay { get; set; }
    /// <summary>
    /// 直属上级的Id
    /// </summary>
    public string ParentId { get; set; }
    private Employee _parent;

    public static Employee query(string id)
    {
        Employee emp = new Employee();
        //实现略,仅需填充emp的熟悉即可
        return emp;
    }
    /// <summary>
    /// 保存对象,实现略
    /// </summary>
    /// <returns></returns>
    public bool Save()
    {
        return true;
    }
    /// <summary>
    /// 删除对象,实现略
    /// </summary>
    /// <returns></returns>
    public bool Drop()
    {
        return true;
    }
    /// <summary>
    /// 上级领导，此处直接获得了Employee对象
    /// </summary>
    public Employee Parent
    {
        get
        {
            if (_parent != null)
            {
                return _parent;
            }
            else
            {
                _parent = query(this.ParentId);
                return _parent;
            }
        }
        set
        {
            _parent = value;
            this.ParentId = _parent.Id;
            Save();
        }
    }
}

Service层

public class EmpService
{
    public void Test()
    {
        Employee emp1 = new Employee() { Id = System.Guid.NewGuid().ToString(), Name = "张三", Sex = "男" };
        Employee emp2 = new Employee() { Id = System.Guid.NewGuid().ToString(), Name = "李四", Sex = "男", ParentId = emp1.Id };
        //插入员工
        emp1.Save();
        emp2.Save();

        //取员工的上级
        var emp2Parent = emp2.Parent;
        var emp2Parent_Parent = emp2Parent.Parent;

        //删除员工
        emp2.Drop();
        emp1.Drop();
    }
}

总结

总结：从两者Service层和BLL　层的代码区分来看，两者都是实现了业务功能和延迟加载。

贫血模型优点是系统的层次结构清楚，各层之间单向依赖。缺点是不够面向对象。

充血模型优点是面向对象，Business Logic符合单一职责，不像在贫血模型里面那样包含所有的业务逻辑太过沉重。缺点是比较复杂，对技术要求更高。