Question

我正在尝试在LINQ to Entities中重写SQL查询。我正在使用LINQPad和我自己的程序集中的类型化datacontext来测试。

我正在尝试重写的SQL查询：

SELECT DISTINCT variantID AS setID, option_value AS name, option_value_description AS description, sort_order as sortOrder
FROM all_products_option_names AS lst
WHERE lst.optionID=14 AND lst.productID IN (SELECT productID FROM all_products_option_names
                                            WHERE optionID=7 AND option_value IN (SELECT name FROM brands
                                                                                  WHERE brandID=1))
ORDER BY sortOrder;

到目前为止我提出的LINQ to Entities查询（由于超时错误而无效）：

from a in all_products_option_names
where a.optionID == 14 && all_products_option_names.Any(x => x.productID == a.productID && x.optionID == 7 && brands.Any(y => y.name == x.option_value && y.brandID == 1))
select new
{
    id = a.variantID,
    name = a.option_value,
    description = a.option_value_description,
    sortOrder = a.sort_order,
}

这是我运行上述查询时遇到的错误：An error occurred while executing the command definition. See the inner exception for details.

内部例外是：Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.

修改

我使用MySQL，这可能就是LINQPad没有向我展示生成的SQL的原因。

SQL版本没有超时。

编辑2：

我通过完全更改查询来解决问题，所以这个问题现在无关紧要了。

我认为史蒂文的反应是正确的，因为他最接近我想要实现的目标，他的反应给了我这个让我解决问题的想法。

Answer 1

试试这个：

var brandNames =
    from brand in db.Brands
    where brand.ID == 1
    select name;

var brandProductNames =
    from p in db.all_products_option_names
    where p.optionID == 7
    where brandNames.Contains(p.option_value)
    select p.productId;

var results =
    from p in db.all_products_option_names
    where p.optionID == 14
    where brandProductNames.Contains(p.productId)
    select new
    {
        setID = p.variantID, 
        name = p.option_value, 
        description = p.option_value_description, 
        sortOrder = p.sort_order
    };

Answer 2

我建议你做加入而不是子选择。当您查看性能时，子选择效率不高，就像在编码时在循环内部循环，这不是一个好主意。如果您的数据库运行缓慢，这实际上可能导致您获得超时，即使您看起来像一个简单的查询。

Answer 3

我最后会尝试使用joins distinct，如下所示：

var results =
    (from p in db.all_products_option_names
     join p2 in db.all_products_option_names on p.productId equals p2.productId
     join b in db.Brands on p2.option_value equals b.name
     where p.optionID == 14
     where p2.optionID == 7
     where b.BrandID == 1
     select new
     {
        setID = p.variantID, 
        name = p.option_value, 
        description = p.option_value_description, 
        sortOrder = p.sort_order
     }).Distinct();

或者您可以尝试将joins与into和any一样使用

 var results =
         from p in db.all_products_option_names
         join p2 in (from p3 in db.all_products_option_names.Where(x => x.optionId == 7) 
                     join b in db.Brands.Where(x => x.BrandID == 1) on p3.option_value equals b.name 
                     select p3) into pg
         where p.optionID == 14
         where pg.Any()
         select new
         {
            setID = p.variantID, 
            name = p.option_value, 
            description = p.option_value_description, 
            sortOrder = p.sort_order
         };

如何在LINQ to Entities中重写SQL查询？

3 个答案: