将 Linq 合并到 EF

发布于 2024-10-25 16:57:08 字数 587 浏览 1 评论 0原文

我想在删除品牌之前检查该品牌是否存在任何产品。我编写了以下 Linq to 实体框架代码

            int count =0;
            if(!_entitiesContext.Product.Any(p=>p.BrandID==brandID))
            {
                var brand =
                    (from c in _entitiesContext.Brand
                     where c.BrandID == brandID 
                     select c).FirstOrDefault();

                _entitiesContext.DeleteObject(brand);
                count = _entitiesContext.SaveChanges();
            }

            return count>0;

上面的代码将访问数据库两次，如何将两者结合起来，以便生成一个使用 EXISTS 关键字的 sql 查询？

原文

I want to check if there is any product exist in a brand before deleting the brand. I write the following Linq to entity framework code

            int count =0;
            if(!_entitiesContext.Product.Any(p=>p.BrandID==brandID))
            {
                var brand =
                    (from c in _entitiesContext.Brand
                     where c.BrandID == brandID 
                     select c).FirstOrDefault();

                _entitiesContext.DeleteObject(brand);
                count = _entitiesContext.SaveChanges();
            }

            return count>0;

The above code will access the database twice, how can I combine the two so that one sql query using EXISTS keyword is generated?

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

阳光下的泡沫是彩色的 2024-11-01 16:57:08

如果您从左连接中没有得到任何结果，那么您就知道该品牌没有产品。

尝试，

var query1 = from b in _entitiesContext.Brand
            join p in _entitiesContext.Product on
            on b.BrandID equals p.BrandID
                into bpGroup
                where b.BrandID == brandID
            select new 
            {
              Brand = b
            ,  Count = bpGroup.Count()
            };

if (Count == 0 )
{
    // delete Brand
}

If you get no result back from a left join, then you know there are no products for that brand.

Try,

var query1 = from b in _entitiesContext.Brand
            join p in _entitiesContext.Product on
            on b.BrandID equals p.BrandID
                into bpGroup
                where b.BrandID == brandID
            select new 
            {
              Brand = b
            ,  Count = bpGroup.Count()
            };

if (Count == 0 )
{
    // delete Brand
}

回复收藏 0 原文

~没有更多了~