设计模式-规约模式C#版

设计模式-规约模式C#版

规约模式的使用场景就是规则，业务规则的碎片化。

业务规则的组合是不固定的，需要做成很容易组合，也很容易拆散的方式，规约模式是一个选择。

下面的例子是一个书店中，用户租书的场景。

需要判断用户的最大租书数和用户的状态，需要同时满足这两个要求，才可以继续租书。最大租书数和状态这两个规则拆散开来，在需要的时候再进行组合。不需要组合的地方，就单独使用这些规则。

针对一个实体有不同的规则，把这些规则碎片化，随意组合和拆散，这样就构成了规约模式。

1. using System;
2. using System.Collections.Generic;
3. using System.Linq;
4. using System.Text;
5. namespace DomainModel.Model
6. {
7. ///
8. /// 规约模式
9. ///
10. ///
11. public interface ISpecification
12. {
13. bool IsSatisfiedBy(T entity);
14. ///
15. /// 与规约
16. ///
17. ///
18. ///
19. ISpecification And(ISpecification specification);
20. ///
21. /// 或规约
22. ///
23. ///
24. ///
25. ISpecification Or(ISpecification specification);
26. ///
27. /// 非规约
28. ///
29. ///
30. ISpecification Not();
31. }
32. public class Customer
33. {
34. private ISpecification _hasReachedMax;
35. private ISpecification _active;
36. public Customer(ISpecification hasReachedMax, ISpecification active)
37. {
38. this._hasReachedMax = hasReachedMax;
39. this._active = active;
40. }
41. public int TotalRentNumber { get; set; }
42. public bool Active
43. {
44. get { return true; }
45. }
46. public bool CanRent()
47. {
48. var specification = this._hasReachedMax.Not().And(this._active.Not());
49. return specification.IsSatisfiedBy(this);
50. }
51. }
52. public class HasReachedMaxSpecification : CompositeSpecification
53. {
54. public override bool IsSatisfiedBy(Customer entity)
55. {
56. return entity.TotalRentNumber >= 6;
57. }
58. }
59. public class CustomerActiveSpecification : CompositeSpecification
60. {
61. public override bool IsSatisfiedBy(Customer entity)
62. {
63. return entity.Active;
64. }
65. }
66. ///
67. /// 组合规约
68. ///
69. ///
70. public abstract class CompositeSpecification : ISpecification
71. {
72. public abstract bool IsSatisfiedBy(T entity);
73. public ISpecification And(ISpecification specification)
74. {
75. return new AndSpecification(this, specification);
76. }
77. public ISpecification Not()
78. {
79. return new NotSpecification(this);
80. }
81. public ISpecification Or(ISpecification specification)
82. {
83. throw new NotImplementedException();
84. }
85. }
86. public class AndSpecification : CompositeSpecification
87. {
88. private ISpecification _left;
89. private ISpecification _right;
90. public AndSpecification(ISpecification left, ISpecification right)
91. {
92. this._left = left;
93. this._right = right;
94. }
95. public override bool IsSatisfiedBy(T entity)
96. {
97. return this._left.IsSatisfiedBy(entity) && this._right.IsSatisfiedBy(entity);
98. }
99. }
100. public class OrSpecification : CompositeSpecification
101. {
102. private ISpecification _left;
103. private ISpecification _right;
104. public OrSpecification(ISpecification left, ISpecification right)
105. {
106. this._left = left;
107. this._right = right;
108. }
109. public override bool IsSatisfiedBy(T entity)
110. {
111. return this._left.IsSatisfiedBy(entity) || this._right.IsSatisfiedBy(entity);
112. }
113. }
114. public class NotSpecification : CompositeSpecification
115. {
116. private ISpecification _inner;
117. public NotSpecification(ISpecification inner)
118. {
119. this._inner = inner;
120. }
121. public override bool IsSatisfiedBy(T entity)
122. {
123. return !this._inner.IsSatisfiedBy(entity);
124. }
125. }
126. }

参考文献

1.走向.NET架构设计-第五章-业务层模式，原则，实践（前篇）