实体层,事实上就是数据库的对象化,把数据表抽象化,目前有很多这方面的工具,我们把这些工具称为ORM工具,即对象关系模型,microsoft在进入3.5时代后引入了LINQ的概念,LINQ的出现,大大提高了开发人员工作效率,它把传统的数据库直接对象了,并以IQueryable<T>的形式被以提供访问，它被称为是可查询的结果集，我们也可以把它理解为是一个ＶＳ项目里的数据库．

不说费话了，还是看看我的实体设计吧！

1:  #region 对实体层的实现

2:      /// 

3:      /// 实体通用接口

4:      /// 

5:      public interface IDataEntity

6:      {

7:      }

8:      /// 

9:      /// 实体验证接口

10:      /// 

11:      public interface IEntity

12:      {

13:          /// 

14:          /// 实体是否有效,只提供读方法,它直接返回本类某方法的类即可,所以不提供set

15:          /// 

16:          bool IsValid { get; }

17:          /// 

18:          /// 验证迭代器

19:          /// 

20:          /// 
     

21:          IEnumerable
     
       GetRuleViolations();
     

22:      }

23:      /// 

24:      /// 验证类结构

25:      /// 

26:      public class RuleViolation

27:      {

28:          public string ErrorMessage { get; private set; }

29:          public string PropertyName { get; private set; }

30:          public RuleViolation(string propertyName, string errorMessage)

31:          {

32:              this.ErrorMessage = errorMessage;

33:              this.PropertyName = propertyName;

34:          }

35:          public RuleViolation(string errorMessage)

36:          {

37:              this.ErrorMessage = errorMessage;

38:          }

39:      }

40:      public partial class Department : IDataEntity

41:      {

42:          //初始字段

43:          #region original field

44:   

45:          /// 

46:          ///

47:          /// 

48:          public int DeptID { get; set; }

49:   

50:          /// 

51:          ///

52:          /// 

53:          public string DeptName { get; set; }

54:   

55:          /// 

56:          ///

57:          /// 

58:          public DateTime CreateDate { get; set; }

59:   

60:          /// 

61:          ///

62:          /// 

63:          public DateTime UpdateDate { get; set; }

64:   

65:          /// 

66:          ///

67:          /// 

68:          public string Operator { get; set; }

69:   

70:          /// 

71:          /// 上一级ID，最高级别的父ID为0

72:          /// 

73:          public int ParentID { get; set; }

74:   

75:          #endregion

76:

77:          //外延字段

78:          #region extensional field

79:          #endregion

80:

81:          //构造函数

82:          #region constructed function

83:   

84:          /// 

85:          /// 新建立的时候构造函数

86:          /// 

87:          public Department()

88:          {

89:   

90:          }

91:   

92:          /// 

93:          /// 新建立的时候构造函数

94:          /// 

95:          /// 

96:          public Department(Int32 _DeptID)

97:          {

98:              this.DeptID = _DeptID;

99:   

100:          }

101:   

102:          #endregion

103:

104:          //方法

105:          #region function

106:   

107:          #endregion

108:

109:          //重写方法

110:          #region object overrides

111:   

112:          #endregion

113:      }

114:   

115:      public partial class Department : IEntity

116:      {

117:   

118:          #region IEntity 成员

119:   

120:          public bool IsValid

121:          {

122:              get { return (GetRuleViolations().Count() == 0); }

123:          }

124:   

125:          public IEnumerable
     
       GetRuleViolations()
     

126:          {

127:              if (String.IsNullOrEmpty(this.DeptName))

128:                  yield return new RuleViolation("不能为空", "DeptName");

129:              if (String.IsNullOrEmpty(this.Operator))

130:                  yield return new RuleViolation("不能为空", "Operator");

131:              yield break;

132:          }

133:   

134:          #endregion

135:      }

136:   

137:      #endregion

看清楚了吧，我们的实体是由两部分组成了，即＂实体的基本属性＂和＂实体的验证机制＂哈哈

去感受吧！