良好的类设计的例子 [英] Good class design by example

问题描述

我试图找出最好的方法来设计一个类，它的属性保存在数据库中。让我们举一个 Person 的一个基本例子。要创建一个新的人并将它放在数据库中，我想让 DateOfBirth 属性是可选的（即在数据库中为NULLable）。

I am trying to work out the best way to design a class that has its properties persisted in a database. Let's take a basic example of a Person. To create a new person and place it in the database, I want the DateOfBirth property to be optional (i.e. NULLable in the DB).

这是我的示例代码：

namespace BusinessLayer
{
    class Person
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public DateTime DateOfBirth { get; set; }
    }
}

我不确定字段是否应该公开或不公开。我应该这样做：

I'm unsure as to whether the fields should be public or not. Should I do it like this:

class Program
{
    static void Main(string[] args)
    {
        Person person1 = new Person("Kate","Middleton",null);
    }
}

或这样：

class Program
{
    static void Main(string[] args)
    {
        Person person1 = new Person();
        person1.FirstName = "Kate";
        person1.LastName = "Middleton";
    }
}

我也想知道我应该如何处理该类的可选属性。填充字段后，如何将它们保存到DB？我有一个DatabaseComponenet类来保存信息。

I'm also wondering how I should be dealing with the optional properties of the class. Once the fields have been populated how do I then save them to the DB? I have a DatabaseComponenet class to save the information. How do I deal with the optional when saving to the database?

所以，我会这样做：

public int Save()
{
    int personId;
    personId = DatabaseComponent.InsertPerson(FirstName, LastName, DateOfBirth);
    return personId;
}

感谢任何帮助！

推荐答案

首先，我将两个不同的公共构造函数赋给Person：

First, I'd put two distinct public constructor to Person:

namespace BusinessLayer
{
    class Person
    {
        public Person(string firstName, string lastName): this(firstName, lastName, DateTime.Now)
        {}

        public Person(string firstName, string lastName, DateTime birthDate)
        {
            FirstName = firstName;
            LastName = lastName;
            DateOfBirth = birthDate;
        }

        public string FirstName { get; set; }
        public string LastName { get; set; }
        public DateTime DateOfBirth { get; set; }
    }
}

this allows you to write both

var p = new Person("Marilyin", "Manson");
var p2 = new Person("Alice", "Cooper", new DateTime(...));

和

var p = new Person { FirstName="Marilyn", LastName="Manson" };

我不明白为什么你应该只限制一个表单。

I can't see why you should limit to only one form.

至于DatabaseComponent，我强烈建议你写一个方法，让你保存一个Person，而不是隐式声明的签名。

As for the DatabaseComponent I'd strongly suggest to write a method that allows you to save a Person instead of the signature you are implicitly declaring.

这是因为，如果有一天改变了Person定义的方式，你可能需要改变每个调用 Save（）方法的代码。通过保存一个Person，你只需要改变 Save（）实现。

That's because, should one day change the way a Person is defined, you'd probably have to change the code in each point you invoke Save() method. By saving just a Person, you only have to change the Save() implementation.

要使用ORM吗？

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