Question

在应用程序中我有两个模型类别和产品。显示如下

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int CategoryId { get; set; }
}
public class Category
{
    public Category()
    {
        Products = new List<Product>();
    }
    public int Id { get; set; }
    public string Name { get; set; }
    public List<Product> Products { get; set; }
}

我将数据添加到类别和产品列表中，如下所示。

List<Category> data = new List<Category>();
data.Add(new Category { Id = 1, Name = "Plastic"});
data.Add(new Category { Id = 2, Name = "Metal"});
data.Add(new Category { Id = 3, Name = "Paper" });
foreach (var item in data)
{
    switch (item.Id)
    {
        case 1: 
            item.Products.Add(new Product { Id = 1, Name = "Doll", CategoryId = item.Id });
            item.Products.Add(new Product { Id = 2, Name = "Pen", CategoryId = item.Id });
            break;
        case 2: 
            item.Products.Add(new Product { Id = 3, Name = "Nail", CategoryId = item.Id });
            item.Products.Add(new Product { Id = 4, Name = "Key", CategoryId = item.Id });
            break;
        case 3: 
            item.Products.Add(new Product { Id = 5, Name = "Book", CategoryId = item.Id });
            break;
        default: 
            item.Products.Add(new Product { Id = 0, Name = null });
            break;
    }
}

还有其他方法可以用最少的代码行编写吗？如果有人为此提出另一种解决方案，我将不胜感激。

Answer 1

您可以提供流畅的构建器方法来将产品添加到类别（它可以是扩展方法或类别的实例方法）。这些方法应返回添加产品的类别。用法看起来像（将产品添加到类别有三种不同的选项）：

var data = new List<Category> {       
   new Category { Id = 1, Name = "Plastic" } 
      .WithProducts(  
          new Product { Id = 1, Name = "Doll" }
          new Product { Id = 2, Name = "Pen" }
      ),

   new Category { Id = 3, Name = "Paper" }
      .WithProduct( new Product { Id = 2, Name = "Book" } ),

   new Category { Id = 2, Name = "Plastic" }
      .WithProduct(3, "Nail")
      .WithProduct(4, "Key"),
};

流畅的扩展方法（你可以使用all，或者选择你更喜欢的语法）：

public static Category WithProduct(this Category category, int id, string product)
{
    category.Products.Add(new Product { Id = id, Name = name, CategoryId = category.Id });
    return category;
}

public static Category WithProduct(this Category category, Product product)
{
    product.CategoryId = category.Id;
    category.Products.Add(product);
    return category;
}

public static Category WithProducts(this Category category, params Product[] products)
{
    foreach(var product in products)
    {
        product.CategoryId = category.Id;
        category.Products.Add(product);
    };

    return category;
}

请注意，将产品添加到类别时，系统会自动设置类别ID。

进一步说明：您的设计存在一个问题 - 当您公开类别Products和类别ID以进行修改时，有人可能会将其他类别的产品添加到产品列表中：

var plastic = new Category { Id = 1, Name = "Plastic"};
plastic.Products.Add(new Product {Id = 1, Name = "Doll", CategoryId = 1});
plastic.Products.Add(new Product {Id = 5, Name = "Nail", CategoryId = 2}); // plastic nail

我至少会考虑禁用类别产品的直接修改，并在那里移动产品的设置类别ID：

private List<Product> products = new List<Product>();
public IEnumerable<Product> Products => products;

public void AddProduct(Product product)
{
    // probably check if product was not added to some other category
    product.CategoryId = Id;
    products.Add(product);
}

Answer 2

由于它处理对象创建，所以没有什么会明显缩短，所以你必须进行这些新的调用。你可以做点像......

在您的Product class上创建一个名为Create：

的静态方法

public static Product Create(int id, string name, Category cat)
{
    return new Product { Id = id, Name = name, cat.Id };
}

然后而不是写作：

item.Products.Add(new Product { Id = 1, Name = "Doll", CategoryId = item.Id });

写：

item.Products.Add(Product.Create(1, "Doll", item);

Answer 3

我会做类似于谢尔盖别列佐夫斯基建议的事情，但我也会在两个类中添加构造函数。扩展方法很好，但是，您也可以为Category类创建一个公共方法。

这是输出：

var categories = new List<Category>
{
    new Category(1, "Plastic").WithProduct(1, "Doll").WithProduct(2, "Pen"),
    new Category(2, "Metal").WithProduct(3, "Nail").WithProduct(4, "Key"),
    new Category(3, "Paper").WithProduct(5, "Book")
};

这是修改后的Product类：

public class Product
{
    public Product(int id, string name, int categoryId)
    {
        Id = id;
        Name = name;
        CategoryId = categoryId;
    }

    public int Id { get; set; }
    public string Name { get; set; }
    public int CategoryId { get; set; }
}

这是修改后的Category类：

public class Category
{
    public Category(int id, string name)
    {
        Id = id;
        Name = name;
        Products = new List<Product>();
    }

    public int Id { get; set; }
    public string Name { get; set; }
    public List<Product> Products { get; set; }

    public Category WithProduct(int id, string name)
    {
        Products.Add(new Product(id, name, Id));
        return this;
    }
}

是否有其他方法将列表的模型类添加到c＃中的另一个模型类列表中？

3 个答案: