得到一个错误“不支持”.用户代码“未处理”异常

本文关键字：未处理 不支持 代码 异常 用户 错误 一个 | 更新日期: 2023-09-27 18:05:56

我有一个表

  product(table name)
        product_id
        product_name 
        product_image
        product_price
        product_description
        category_id
  category(table name )
        category_id
        category_name 
        category_description

我有一个命名为categoryCombobox的组合框和命名为productgridview的网格视图

我试图根据组合框中的选择填充数据网格。像这样....

       private viod form_load(object sender, EventArgs e)
       {
        var products = from prods in abc.products
                       select new
                       {
                           prods.product_Id,
                           productname =  prods.product_Name,
                           productimage = prods.product_Image,
                           productprice = prods.product_Price,
                           productdescription = prods.product_Description
                       };
        productbindingsource.DataSource = products;
        productgridview.DataSource = productbindingsource;
        productgridview.Columns[0].Visible = false;
       }
       private void categoryCombobox_SelectedIndexChanged(object sender, EventArgs e)
       {
          // is this query correct 
          var categoryid = from productcategories in abc.categories
                         where productcategories.category_Name.Equals(categoryCombobox.Text)
                         select productcategories.category_Id;
          var produc = from pros in abc.products
                       where pros.Category_Id.Equals(categoryid)
                       select new
                       {
                           productname = pros.product_Name,
                           productimage = pros.product_Image,
                           productprice = pros.product_Price,
                           productdescription = pros.product_Description                                   
                       };
        productbindingsource.DataSource = produc;
        productgridview.DataSource = productbindingsource;
        productgridview.Columns[0].Visible = false;
    }

出现如下错误......

错误:在这一行productindingsource。数据源= product;

用户代码未处理不支持的异常
不能比较'System.Linq.IQueryable ' 1'类型的元素。只有基本类型(如Int32、String和Guid)和实体支持的类型

得到一个错误“不支持”.用户代码“未处理”异常

var categoryid = from productcategories in abc.categories
                 where productcategories.
                           category_Name.Equals(categoryCombobox.Text)
                 select productcategories.category_Id;

在调试时悬停在var上。您将看到它不是您所期望的id，而是IEnumerable。你要做的是

// .First() trips the query and returns a single category_Id
var id = (from productcategories in abc.categories
         where productcategories.
                   category_Name.Equals(categoryCombobox.Text)
         select productcategories.category_Id).First();
var produc = from pros in abc.products
               where pros.Category_Id.Equals(id)
               select new
               {
                   productname = pros.product_Name,
                   productimage = pros.product_Image,
                   productprice = pros.product_Price,
                   productdescription = pros.product_Description                                   
               };

注意ids.First()，它获取初始查询的第一个结果。

您正在尝试将int字段与可枚举集进行比较。

如果categoryID查询只返回一个值，那么试试这个:

var produc = from pros in abc.products
                   where pros.Category_Id.Equals(categoryid.Single())
                   select new
                   {
                       productname = pros.product_Name,
                       productimage = pros.product_Image,
                       productprice = pros.product_Price,
                       productdescription = pros.product_Description                                   
                   };

如果它应该返回一个id列表，您将需要编写一个带有连接的单个查询。我假设它应该是单基于名称categoryId

edit -可能不是100%语法正确

var produc = from pros in abc.products
    join cats in abc.categories on cats.category_id equals pros.Category_Id
    where cats.category_Name.Equals(categoryCombobox.Text)
    select new
    {
        productname = pros.product_Name,
        productimage = pros.product_Image,
        productprice = pros.product_Price,
        productdescription = pros.product_Description                                   
    };
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