无法创建常量值 - 仅原始类型

Question

两个简单的查询 - 例外情况发生在:

matchings.Any(u => product.ProductId == u.ProductId)

怎么了？如果我写作true而不是一切都很好.

var matchings = (from match in db.matchings 
                 where match.StoreId == StoreId 
                 select match).ToList();

var names = (from product in db.Products
             where matchings.Any(u => product.ProductId == u.ProductId)
             select product).ToList();

Answer 1

第一种方式:

ToList()在第一个查询中删除.

要么

//instead of retrieving mathings List, retrieve only the productIds you need (which are a List of Primitive types)
var productIdList = db.matchings
.Where(m => m.StoreId == StoreId)
.Select(x => x.ProductId)
.ToList();

var products = db.Products
.Where(p => productIdList
           .Contains(p.ProductId))
.ToList();

要么

//other way
var produts = db.Products
             .Where(p => db.matchings
                        .Any(m => m.StoreId == StoreId && 
                             m.ProductId == p.ProductId)
                    )
             .ToList();

因为我认为你在linq2entities,并且你在查询中使用匹配列表是不可能的(你的主题的标题往往让我相信这是你的问题).

Answer 2

这看起来像是一个使用join的地方

 var query =
    from product in db.Products
    join matching in db.Matchings
    on product.ProductId equals matching.ProductId into matchGroup
    where matchGroup.Count() > 0 and matching.StoreId == StoreId
    select product;