如何让MonthlyQuota类兼容EmployeeVacationForm与EmployeeVacationForm_Remote？

问题背景 #

现有MonthlyQuota类仅支持EmployeeVacationForm类型，现在需要扩展支持EmployeeVacationForm_Remote类型，且保持原有的调用语法不变：

// 原支持的调用
var staffResults = vacations.Select(vf => new MonthlyQuota(vf));
// 需要新增支持的调用
var staffResults = vacations.Select(rvf => new MonthlyQuota(rvf));

推荐解决方案：抽象基类/接口统一处理 #

这种方式符合面向抽象编程原则，扩展性强，后续新增其他表单类型只需继承基类即可。

步骤1：定义公共基类/接口 #

首先为两种表单类定义一个包含公共属性的基类（或接口）：

// 定义抽象基类，包含两种表单共有的属性和行为
public abstract class BaseEmployeeVacationForm
{
    public DateTime? DateCreated { get; set; }
    public MonthlyQuota QuotaResult { get; set; }
}

// 让现有表单类继承基类
public class EmployeeVacationForm : BaseEmployeeVacationForm
{
    // 原有业务逻辑代码
}

// 远程表单类同样继承基类
public class EmployeeVacationForm_Remote : BaseEmployeeVacationForm
{
    // 远程表单特有业务逻辑代码
}

步骤2：修改MonthlyQuota类 #

将Form属性改为基类类型，并添加对应构造函数：

public class MonthlyQuota
{
    // 改为基类类型，兼容所有继承自BaseEmployeeVacationForm的子类
    public virtual BaseEmployeeVacationForm Form { get; set; }
    
    // DateEmployeeSubmitted逻辑无需修改，因为基类已包含DateCreated属性
    public virtual DateTime? DateEmployeeSubmitted => Form?.DateCreated;

    // 保留原有构造函数
    public MonthlyQuota(QuarterlySupport document)
    {
        Document = document;
    }

    // 修改内部构造函数的参数类型为基类
    internal MonthlyQuota(QuarterlySupport document, BaseEmployeeVacationForm form)
        : this(document)
    {
        Form = form;
        form.QuotaResult = this;
    }

    // 添加直接接受EmployeeVacationForm的公共构造函数，兼容原调用
    public MonthlyQuota(EmployeeVacationForm form)
        : this(null, form)
    {
    }

    // 添加接受EmployeeVacationForm_Remote的公共构造函数，支持新调用
    public MonthlyQuota(EmployeeVacationForm_Remote form)
        : this(null, form)
    {
    }

    // 补充原代码中缺失的Document属性定义
    public QuarterlySupport Document { get; set; }
}

备选方案：泛型实现 #

如果不需要统一抽象处理，也可以用泛型方式实现，适合临时扩展场景：

// 先定义约束接口，确保泛型类型包含必要属性
public interface IVacationForm
{
    DateTime? DateCreated { get; set; }
    MonthlyQuota<IVacationForm> QuotaResult { get; set; }
}

// 让两种表单实现接口
public class EmployeeVacationForm : IVacationForm
{
    public DateTime? DateCreated { get; set; }
    public MonthlyQuota<IVacationForm> QuotaResult { get; set; }
    // 原有业务代码
}

public class EmployeeVacationForm_Remote : IVacationForm
{
    public DateTime? DateCreated { get; set; }
    public MonthlyQuota<IVacationForm> QuotaResult { get; set; }
    // 远程表单特有代码
}

// 修改为泛型类
public class MonthlyQuota<TForm> where TForm : IVacationForm
{
    public virtual TForm Form { get; set; }
    
    public virtual DateTime? DateEmployeeSubmitted => Form?.DateCreated;

    public MonthlyQuota(QuarterlySupport document)
    {
        Document = document;
    }

    internal MonthlyQuota(QuarterlySupport document, TForm form)
        : this(document)
    {
        Form = form;
        form.QuotaResult = this as MonthlyQuota<IVacationForm>;
    }

    public MonthlyQuota(TForm form)
        : this(null, form)
    {
    }

    public QuarterlySupport Document { get; set; }
}

调用时编译器会自动推断泛型类型：

var staffResults = vacations.Select(vf => new MonthlyQuota<EmployeeVacationForm>(vf));
var remoteStaffResults = remoteVacations.Select(rvf => new MonthlyQuota<EmployeeVacationForm_Remote>(rvf));

内容的提问来源于stack exchange，提问作者SkyeBoniwell