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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。
- using System;
- using System.Collections.Generic;
- using System.Linq;
- using System.Text;
- namespace DomainModel.Model
- {
- /// <summary>
- /// 规约模式
- /// </summary>
- /// <typeparam name="T"></typeparam>
- public interface ISpecification<T>
- {
- bool IsSatisfiedBy(T entity);
- /// <summary>
- /// 与规约
- /// </summary>
- /// <param name="specification"></param>
- /// <returns></returns>
- ISpecification<T> And(ISpecification<T> specification);
- /// <summary>
- /// 或规约
- /// </summary>
- /// <param name="specification"></param>
- /// <returns></returns>
- ISpecification<T> Or(ISpecification<T> specification);
- /// <summary>
- /// 非规约
- /// </summary>
- /// <returns></returns>
- ISpecification<T> Not();
- }
- public class Customer
- {
- private ISpecification<Customer> _hasReachedMax;
- private ISpecification<Customer> _active;
- public Customer(ISpecification<Customer> hasReachedMax, ISpecification<Customer> active)
- {
- this._hasReachedMax = hasReachedMax;
- this._active = active;
- }
- public int TotalRentNumber { get; set; }
- public bool Active
- {
- get { return true; }
- }
- public bool CanRent()
- {
- var specification = this._hasReachedMax.Not().And(this._active.Not());
- return specification.IsSatisfiedBy(this);
- }
- }
- public class HasReachedMaxSpecification : CompositeSpecification<Customer>
- {
- public override bool IsSatisfiedBy(Customer entity)
- {
- return entity.TotalRentNumber >= 6;
- }
- }
- public class CustomerActiveSpecification : CompositeSpecification<Customer>
- {
- public override bool IsSatisfiedBy(Customer entity)
- {
- return entity.Active;
- }
- }
- /// <summary>
- /// 组合规约
- /// </summary>
- /// <typeparam name="T"></typeparam>
- public abstract class CompositeSpecification<T> : ISpecification<T>
- {
- public abstract bool IsSatisfiedBy(T entity);
- public ISpecification<T> And(ISpecification<T> specification)
- {
- return new AndSpecification<T>(this, specification);
- }
- public ISpecification<T> Not()
- {
- return new NotSpecification<T>(this);
- }
- public ISpecification<T> Or(ISpecification<T> specification)
- {
- throw new NotImplementedException();
- }
- }
- public class AndSpecification<T> : CompositeSpecification<T>
- {
- private ISpecification<T> _left;
- private ISpecification<T> _right;
- public AndSpecification(ISpecification<T> left, ISpecification<T> right)
- {
- this._left = left;
- this._right = right;
- }
- public override bool IsSatisfiedBy(T entity)
- {
- return this._left.IsSatisfiedBy(entity) && this._right.IsSatisfiedBy(entity);
- }
- }
- public class OrSpecification<T> : CompositeSpecification<T>
- {
- private ISpecification<T> _left;
- private ISpecification<T> _right;
- public OrSpecification(ISpecification<T> left, ISpecification<T> right)
- {
- this._left = left;
- this._right = right;
- }
- public override bool IsSatisfiedBy(T entity)
- {
- return this._left.IsSatisfiedBy(entity) || this._right.IsSatisfiedBy(entity);
- }
- }
- public class NotSpecification<T> : CompositeSpecification<T>
- {
- private ISpecification<T> _inner;
- public NotSpecification(ISpecification<T> inner)
- {
- this._inner = inner;
- }
- public override bool IsSatisfiedBy(T entity)
- {
- 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)
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