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。

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;namespaceDomainModel.Model{///<summary>///规约模式///</summary>///<typeparamname="T"></typeparam>publicinterfaceISpecification<T>{boolIsSatisfiedBy(Tentity);///<summary>///与规约///</summary>///<paramname="specification"></param>///<returns></returns>ISpecification<T>And(ISpecification<T>specification);///<summary>///或规约///</summary>///<paramname="specification"></param>///<returns></returns>ISpecification<T>Or(ISpecification<T>specification);///<summary>///非规约///</summary>///<returns></returns>ISpecification<T>Not();}publicclassCustomer{privateISpecification<Customer>_hasReachedMax;privateISpecification<Customer>_active;publicCustomer(ISpecification<Customer>hasReachedMax,ISpecification<Customer>active){this._hasReachedMax=hasReachedMax;this._active=active;}publicintTotalRentNumber{get;set;}publicboolActive{get{returntrue;}}publicboolCanRent(){varspecification=this._hasReachedMax.Not().And(this._active.Not());returnspecification.IsSatisfiedBy(this);}}publicclassHasReachedMaxSpecification:CompositeSpecification<Customer>{publicoverrideboolIsSatisfiedBy(Customerentity){returnentity.TotalRentNumber>=6;}}publicclassCustomerActiveSpecification:CompositeSpecification<Customer>{publicoverrideboolIsSatisfiedBy(Customerentity){returnentity.Active;}}///<summary>///组合规约///</summary>///<typeparamname="T"></typeparam>publicabstractclassCompositeSpecification<T>:ISpecification<T>{publicabstractboolIsSatisfiedBy(Tentity);publicISpecification<T>And(ISpecification<T>specification){returnnewAndSpecification<T>(this,specification);}publicISpecification<T>Not(){returnnewNotSpecification<T>(this);}publicISpecification<T>Or(ISpecification<T>specification){thrownewNotImplementedException();}}publicclassAndSpecification<T>:CompositeSpecification<T>{privateISpecification<T>_left;privateISpecification<T>_right;publicAndSpecification(ISpecification<T>left,ISpecification<T>right){this._left=left;this._right=right;}publicoverrideboolIsSatisfiedBy(Tentity){returnthis._left.IsSatisfiedBy(entity)&&this._right.IsSatisfiedBy(entity);}}publicclassOrSpecification<T>:CompositeSpecification<T>{privateISpecification<T>_left;privateISpecification<T>_right;publicOrSpecification(ISpecification<T>left,ISpecification<T>right){this._left=left;this._right=right;}publicoverrideboolIsSatisfiedBy(Tentity){returnthis._left.IsSatisfiedBy(entity)||this._right.IsSatisfiedBy(entity);}}publicclassNotSpecification<T>:CompositeSpecification<T>{privateISpecification<T>_inner;publicNotSpecification(ISpecification<T>inner){this._inner=inner;}publicoverrideboolIsSatisfiedBy(Tentity){return!this._inner.IsSatisfiedBy(entity);}}}

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）