使用LINQ在子查询中进行高级多重连接
题
我花了整个下午的时间试图将我的想法转化为如何将以下查询转换为LINQ,但我无法完全实现。
declare @productId int; set @productId = 3212;
select * from InformationData data where productId = @productId and orgId = 1
and exists(
select id from (
select coalesce(id1.id, id2.id, id3.id) as id from (
select productId,attributeId from InformationData where productId = @productId group by productId,attributeId
) id
left outer join InformationData id1 on id1.productId = id.productId and id1.attributeId = id.attributeId and id1.language = 1
left outer join InformationData id2 on id2.productId = id.productId and id2.attributeId = id.attributeId and id2.language = 2
left outer join InformationData id3 on id3.productId = id.productId and id3.attributeId = id.attributeId and id3.language = 0
) row
where row.id = data.id
)
查询的目的是使用2种后备语言从表中获取数据,因此如果语言1中不存在数据,则使用语言2获取数据,如果2不存在,则获取语言0这是一个全球翻译。
我可以得到内部查询大多正确(除了来自id1.language = 1,我似乎无法加入我加入的表的成员,任何想法?)
这是我的代码(LINQPad代码):
(
from data in (
from d in InformationData where d.ProductId == 3212 group d by new { d.ProductId, d.AttributeId } into p select new { ProductId = p.Key.ProductId, AttributeId = p.Key.AttributeId }
)
join x1 in InformationData on new { a = data.ProductId, b = data.AttributeId } equals new { a = x1.ProductId, b = x1.AttributeId } into f1
from r1 in f1.DefaultIfEmpty()
where r1.Language == 1
join x2 in InformationData on new { a = data.ProductId, b = data.AttributeId } equals new { a = x2.ProductId, b = x2.AttributeId } into f2
from r2 in f2.DefaultIfEmpty()
where r2.Language == 2
join x3 in InformationData on new { a = data.ProductId, b = data.AttributeId } equals new { a = x3.ProductId, b = x3.AttributeId } into f3
from r3 in f3.DefaultIfEmpty()
where r3.Language == 2
select new { Id = ((int?)r1.Id) ?? ((int?)r2.Id) ?? r3.Id }
).Dump();
生成以下SQL:
-- Region Parameters
DECLARE @p0 Int SET @p0 = 3212
DECLARE @p1 Int SET @p1 = 2
DECLARE @p2 Int SET @p2 = 2
DECLARE @p3 Int SET @p3 = 1
-- EndRegion
SELECT COALESCE([t2].[id],COALESCE([t3].[id],[t4].[id])) AS [Id]
FROM (
SELECT [t0].[productId], [t0].[attributeId]
FROM [InformationData] AS [t0]
WHERE [t0].[productId] = @p0
GROUP BY [t0].[productId], [t0].[attributeId]
) AS [t1]
LEFT OUTER JOIN [InformationData] AS [t2] ON ([t1].[productId] = [t2].[productId]) AND ([t1].[attributeId] = [t2].[attributeId])
LEFT OUTER JOIN [InformationData] AS [t3] ON ([t1].[productId] = [t3].[productId]) AND ([t1].[attributeId] = [t3].[attributeId])
LEFT OUTER JOIN [InformationData] AS [t4] ON ([t1].[productId] = [t4].[productId]) AND ([t1].[attributeId] = [t4].[attributeId])
WHERE ([t4].[language] = @p1) AND ([t3].[language] = @p2) AND ([t2].[language] = @p3)
但是我不能把这个和其他的查询放在一起,也许我只是累了买我继续得到它做很多CROSS APPLY的。有没有人有任何建议?
解决方案
经过一夜好眠,一些嘎吱嘎吱的事情变得更加明亮,我找到了解决方案:)对于任何好奇的人来说,这是
(
from i in InformationData
where (
from data in (
from d in InformationData where d.ProductId == 3212 group d by new { d.ProductId, d.AttributeId } into p select new { ProductId = p.Key.ProductId, AttributeId = p.Key.AttributeId }
)
join x1 in InformationData on new { a = data.ProductId, b = data.AttributeId, c = 1} equals new { a = x1.ProductId, b = x1.AttributeId, c = x1.Language } into f1
from r1 in f1.DefaultIfEmpty()
join x2 in InformationData on new { a = data.ProductId, b = data.AttributeId, c = 2 } equals new { a = x2.ProductId, b = x2.AttributeId, c = x2.Language } into f2
from r2 in f2.DefaultIfEmpty()
join x3 in InformationData on new { a = data.ProductId, b = data.AttributeId, c = 0 } equals new { a = x3.ProductId, b = x3.AttributeId, c = x3.Language } into f3
from r3 in f3.DefaultIfEmpty()
select new { Id = ((int?)r1.Id) ?? ((int?)r2.Id) ?? r3.Id }
).Any(d => d.Id == i.Id)
select i
).Dump();
这是生成的SQL
-- Region Parameters
DECLARE @p0 Int SET @p0 = 3212
DECLARE @p1 Int SET @p1 = 1
DECLARE @p2 Int SET @p2 = 2
DECLARE @p3 Int SET @p3 = 0
-- EndRegion
SELECT [t0].[id] AS [Id], [t0].[attributeId] AS [AttributeId], [t0].[productId] AS [ProductId], [t0].[value] AS [Value], [t0].[orgId] AS [OrgId], [t0].[version] AS [Version], [t0].[language] AS [Language], [t0].[metaType] AS [MetaType], [t0].[overload] AS [Overload], [t0].[parentId] AS [ParentId]
FROM [InformationData] AS [t0]
WHERE EXISTS(
SELECT NULL AS [EMPTY]
FROM (
SELECT COALESCE([t3].[id],COALESCE([t4].[id],[t5].[id])) AS [value]
FROM (
SELECT [t1].[productId], [t1].[attributeId]
FROM [InformationData] AS [t1]
WHERE [t1].[productId] = @p0
GROUP BY [t1].[productId], [t1].[attributeId]
) AS [t2]
LEFT OUTER JOIN [InformationData] AS [t3] ON ([t2].[productId] = [t3].[productId]) AND ([t2].[attributeId] = [t3].[attributeId]) AND (@p1 = [t3].[language])
LEFT OUTER JOIN [InformationData] AS [t4] ON ([t2].[productId] = [t4].[productId]) AND ([t2].[attributeId] = [t4].[attributeId]) AND (@p2 = [t4].[language])
LEFT OUTER JOIN [InformationData] AS [t5] ON ([t2].[productId] = [t5].[productId]) AND ([t2].[attributeId] = [t5].[attributeId]) AND (@p3 = [t5].[language])
) AS [t6]
WHERE [t6].[value] = [t0].[id]
)
其他提示
主要基于您对查询应该执行的操作的描述,我认为您可以使用适当的“orderby”来完成相同的结果。子句并只检索第一个结果。像这样:
var result =
(
from d in InformationData
where d.ProductId == 3212
orderby ((d.language == 0) ? Int32.MaxValue : d.language)
select d
).First();
编辑:您可以通过扩展orderby子句来控制搜索优先级。例如,如果优先级应该是2,然后是3,然后是1,那么其他任何东西,你都可以这样做:
var result =
(
from d in InformationData
where d.ProductId == 3212
orderby
(d.language == 2) ? 0
: (d.language == 3) ? 1
: (d.language == 1) ? 2
: Int32.MaxValue
select d
).First();
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