Linq多对多查询求救
我这个需求是多对多 菜品和菜品分类 要根据菜品分类 查出所有菜品信息（包括菜品分类） 就是确定一条分类然后还要再加到查出每个菜品所有分类（这里的分类不止一个）代码如下：

var q = db.foodcategories.First(fc => fc.Id == categoryId);

             var q_a = from qq in q.foods
                       from p in db.pictures
                       //from qfc in q_fc
                       where p.FoodId==qq.Id
                       select new FoodModel
                       {
                           Id = qq.Id,
                           Name = qq.Name,
                           pictureUrl=p.Url,
                           Price = qq.Price,
                           Description = qq.Description,
                           MainIngredient = qq.MainIngredient,
                           MinorIngredient = qq.MinorIngredient,
                           Flavoring = qq.Flavoring,
                           Discount = qq.Discount,
                           Recommended = qq.Recommended 
 
                           ,foodCategories = qq.foodcategories.Select(fc => new FCategoryModel { Name = fc.Name }).AsQueryable()
                       };

这样写会出现以下异常:There is already an open DataReader associated with this Connection which must be closed first. 求助解决方案 没有分了求大神帮忙，在线等 急急急 asp.net? linq asp.net 多对多
[解决办法]
这个提示说明你用到了DataReader但是没有正确关闭。和Linq无关。
[解决办法]
试试

var q = db.foodcategories.First(fc => fc.Id == categoryId);
var q_a = from qq in q.foods
                       join p in db.pictures on qq.Id equals p.FoodId
                       select new FoodModel
                       {
                           Id = qq.Id,
                           Name = qq.Name,
                           pictureUrl=p.Url,
                           Price = qq.Price,
                           Description = qq.Description, 
 
                           MainIngredient = qq.MainIngredient,
                           MinorIngredient = qq.MinorIngredient,
                           Flavoring = qq.Flavoring,
                           Discount = qq.Discount,
                           Recommended = qq.Recommended,
                           foodCategories = qq.foodcategories.Select(fc => new FCategoryModel { Name = fc.Name }).AsQueryable()
                       };

[解决办法]

引用:

Quote: 引用:

试试

var q = db.foodcategories.First(fc => fc.Id == categoryId);
var q_a = from qq in q.foods
                       join p in db.pictures on qq.Id equals p.FoodId
                       select new FoodModel
                       {
                           Id = qq.Id,
                           Name = qq.Name,
                           pictureUrl=p.Url,
                           Price = qq.Price, 
 
                           Description = qq.Description,
                           MainIngredient = qq.MainIngredient,
                           MinorIngredient = qq.MinorIngredient,
                           Flavoring = qq.Flavoring,
                           Discount = qq.Discount,
                           Recommended = qq.Recommended,
                           foodCategories = qq.foodcategories.Select(fc => new FCategoryModel { Name = fc.Name }).AsQueryable()
                       };

谢谢大神指教，能说明为什么这样就行，我那个就不行么？

我估计是inner join引起的吧， 你没写对，注意要对应，你可以测试一下，看看，顺便回馈我一下，
var q_a = from qq in q.foods
join p in db.pictures on qq.Id equals p.FoodId