在所选主要类别的所有子类别中获取所有产品的最佳方法是什么？(What would be the best way to get all the products in all the child ca

在所选主要类别的所有子类别中获取所有产品的最佳方法是什么？(What would be the best way to get all the products in all the child categories of a selected main category?)

在所选主要类别的所有子类别中获取所有产品的最佳方法是什么？

这是我的类文件结构：

public partial class Category { public int Id { get; set; } public string Name { get; set; } public int ParentCategoryId { get; set; } //reference to Id public ICollection<Category> _subcategories; } public partial class ProductCategory { public int Id { get; set; } public int ProductId { get; set; } public int CategoryId { get; set; } public virtual Category Category { get; set; } public virtual Product Product { get; set; } } public partial class Product { public int Id { get; set; } public string Name { get; set; } public ICollection<ProductViewMap> _productViewmap; } public class ProductViewMap { public int ProductId { get; set; } public int ProductViewCount { get; set; }//indicated how many times product has been viewed means most popular product. public virtual Product Product { get; set; } }

这是我尝试过的：

//List to hold all Category Ids of Parent Category Id say for eg:1 List<int> categoryChildList = new List<int>(); var data = (from temp in context.Category where temp.ParentCategoryId == parentCategoryId select new { CategoryId = temp.Id }); if(data.Count() > 0) { foreach (var cat in data) { int _cat = Convert.ToInt32(cat.CategoryId); categoryChildList.Add(_cat); } var tmpList = (from p in Context.ProductCategory join m in context.Product on p.ProductId equals m.Id join n in context.ProductViewMap on m.Id equals n.ProductId where categoryChildList.Contains(p.CategoryId) select m).ToList();

这里出现错误：

对象引用未设置为对象的实例。**

当我删除这一行时，一切正常：

join n in context.ProductViewMap on m.Id equals n.ProductId

任何帮助将不胜感激。

包含样本记录的Sql小提琴： http ：//www.sqlfiddle.com/#！3 / bde6b

如果输入为： 计算机 （parentCategoryId：1），则输出如下

最终输出：

ProductId ProductName

1马力

2比较

3联想

What would be the best way to get all the products in all the child categories of a selected main category?

This is my Class File Structure:

public partial class Category { public int Id { get; set; } public string Name { get; set; } public int ParentCategoryId { get; set; } //reference to Id public ICollection<Category> _subcategories; } public partial class ProductCategory { public int Id { get; set; } public int ProductId { get; set; } public int CategoryId { get; set; } public virtual Category Category { get; set; } public virtual Product Product { get; set; } } public partial class Product { public int Id { get; set; } public string Name { get; set; } public ICollection<ProductViewMap> _productViewmap; } public class ProductViewMap { public int ProductId { get; set; } public int ProductViewCount { get; set; }//indicated how many times product has been viewed means most popular product. public virtual Product Product { get; set; } }

This is what i have tried:

//List to hold all Category Ids of Parent Category Id say for eg:1 List<int> categoryChildList = new List<int>(); var data = (from temp in context.Category where temp.ParentCategoryId == parentCategoryId select new { CategoryId = temp.Id }); if(data.Count() > 0) { foreach (var cat in data) { int _cat = Convert.ToInt32(cat.CategoryId); categoryChildList.Add(_cat); } var tmpList = (from p in Context.ProductCategory join m in context.Product on p.ProductId equals m.Id join n in context.ProductViewMap on m.Id equals n.ProductId where categoryChildList.Contains(p.CategoryId) select m).ToList();

Here error is coming:

Object reference not set to instance of object.**

When i am removing this line then everything works fine:

join n in context.ProductViewMap on m.Id equals n.ProductId

any help would be greatly appreciated.

Sql fiddle which contain sample records:http://www.sqlfiddle.com/#!3/bde6b

If Input is :Computer(parentCategoryId:1) then output is as below

Final output:

ProductId ProductName

1 hp

2 compaq

3 lenovo

最满意答案

如果您要尝试的只是获取Product记录，那么使用扩展方法语法可以这样做：

var products = context.ProductCategory.Where(pc => pc.Category.ParentCategoryID != null && pc.Category.ParentCategoryID == parentCategoryID) .Select(pc => pc.Product) .Distinct() .ToList() .OrderBy(p => p.ProductViewMap.Max(pvm => pvm.ProductViewCount);

所有连接都将由LINQ to Entities生成的SQL查询处理。

If all you're trying to do is to grab the Product records, then using the Extension Method syntax you could do it this way:

var products = context.ProductCategory.Where(pc => pc.Category.ParentCategoryID != null && pc.Category.ParentCategoryID == parentCategoryID) .Select(pc => pc.Product) .Distinct() .ToList() .OrderBy(p => p.ProductViewMap.Max(pvm => pvm.ProductViewCount);

All of the joins will be taken care of by the SQL query generated by LINQ to Entities.