如何从复杂的SQL创建LINQ？

Question

I've this SQL query:

 SELECT D.ID
 FROM Documents AS D
 INNER JOIN DocClasses AS DC WITH (NOLOCK) 
 ON D.DocClass = DC.ID
 INNER JOIN DocSubClasses AS DSC WITH (NOLOCK) 
 ON D.DocSubClass = DSC.ID AND DSC.DocClassID = DC.ID
 INNER JOIN DocPathFolders AS F WITH (NOLOCK) 
 ON D.DocPathFolderID = F.ID
 WHERE 
    DC.ShortName = 'PAY' AND DSC.Name = 'xxxxx' 
    AND UPPER(F.Description) = 'READY TO SEND'

I'm trying to convert this query into LINQ. Here is what I've done so far:

 from D in ctx.Documents
 join DC in ctx.DocClasses on D.DocClass equals DC.ID
 join DSC in ctx.DocSubClasses 
     on new { D.DocSubClass, DSC.DocClassID } equals new { DSC.ID, DC.ID }
 join F in ctx.DocPathFolders 
     on D.DocPathFolderID equals F.ID
 where 
     DC.ShortName == "PAY" 
     && DSC.Name == "xxxxx" 
     && (F.Description).ToUpper() == "READY TO SEND"
 select D.ID;

I'm getting error in this line:

join DSC in ctx.DocSubClasses on new { D.DocSubClass, DSC.DocClassID } equals new { DSC.ID, DC.ID }

Here, I'm getting following error:

The name 'DSC' is not in scope on the left side of 'equals'

The name 'DC' is not in scope on the right side of 'equals'

I'm new in LINQ and that's why I can't solve these error. I would apperciate any suggestion on the above. Thanks.

Answer 1

You should rearrange the properties in the anonymous objects like this:

join DSC in ctx.DocSubClasses 
on new { D.DocSubClass, DC.ID } equals new { DSC.DocClassID, DSC.ID }

Those on the right should be of the table you are joining ( DSC ) and those on the left can be of previous tables

Answer 2

Here is how I've solved my issue:

from D in ctx.Documents
join DC in ctx.DocClasses on D.DocClass equals DC.ID
join DSC in ctx.DocSubClasses on new { D.DocSubClass, DC.ID } equals new { DocSubClass = DSC.ID, ID = DSC.DocClassID }
join F in ctx.DocPathFolders on D.DocPathFolderID equals F.ID
where DC.ShortName == "PAY" && DSC.Name == "xxxx" && (F.Description).ToUpper() == "READY TO SEND"
select D.ID;

Answer 3

只需将DSC切换到等于右侧，将DC切换到左侧，它应该可以正常工作。

join DSC in ctx.DocSubClasses on new { D.DocSubClass, DC.ID } equals new { DSC.ID, DSC.DocClassID}

Answer 4

Hint: Provided you have set your relations appropriately in your database you almost never need to use "join". It is easier to write in LINQ and relations are exposed as "navigational properties". You simply use "dot notation". ie:

var result = from d in ctx.Documents
           where d.DocClasses.Any( dc => dc.ShortName == "PAY" 
              && dc.DocSubClasses.Any( dsc => dsc.Name == "xxxxx" )
              && d.DocPathFolders.Any( dpf => dpf.Description.ToUpper() == "READY TO SEND" )
            select d.ID;

Note: We don't have any idea on your model. I assumed the relations as 1-To-Many. If it were Many-To-1 then you would simply use notation like:

where d.DocClass.ShortName == "PAY" 
                  && d.DocClass.DocSubClass.Name == "xxxxx" 
                  && d.DocPathFolder.Description.ToUpper() == "READY TO SEND" 

HINT2: Download and start using Linqpad from LinqPad.net. It is a great tool where you can not only test your LINQ queries but use as a .Net scratch pad.

Answer 5

You can try with Lambda Join instead of using LINQ .

Your JOIN statements look like below in Lambda .

C# Fiddle

var result = ctx.Documents.Join(ctx.DocClasses , d => new { Id = d.DocClass }, dc => new { Id = dc.ID }, (d, dc) => new { doc = d, docClass = dc }) //INNER JOIN DocClasses  
                          .Join(ctx.DocSubClasses , d => new { sc = d.doc.DocSubClass, Id = d.docClass.ID }, dsc => new { sc = dsc.ID, Id = dsc.DocClassID }, (d, dsc) => new { doc = d, dsc = dsc } ) //INNER JOIN DocSubClasses
                          .Join(ctx.DocPathFolders, d => new { fId = d.doc.doc.DocPathFolderID }, f => new { fId = f.ID }, (d, f) => new { doc = d, f = f }) //INNER JOIN DocPathFolders
                          .Where(x => x.doc.doc.docClass.ShortName == "PAY" && x.doc.dsc.Name == "xxxxx" && x.f.Description.ToUpper() == "READY TO SEND")//Apply where clause
                          .Select(y => y.doc.doc.doc.ID);//Select whatever you want