In a circular reference drawing (A>B>C>A) how to find the link between C and A which makes the three drawing circular?

[Nikita_RAUTELA]

I have 3 drawings A, B and C. I have nested the drawings as A>B, B>C, C>A, which makes the three in circular relation. when I open A, the structure is like A(root)>B>C(leaf), when I open C its like C>A>B, and similarly for B.
According to my understanding when a drawing having circular dependencies is opened, say A,  the circular reference is broken as a dialog pops up to continue opening the drawing(if ok, then the circular link is broken)A>B>C(*>A). I iterate from Root graphNode to the leaf but as soon as I reach the leaf the count for the out referencing is 0, which is not true as leaf is parent to the root(making it circular)(C>A). 
How can I get the link from C>A as the link between C and A is still maintained in other drawings(C>A>B)?
Is there any object that is the single source of truth for a drawing and that holds the information of wherever the drawing is referenced?

Currently I am using AcDbXrefGraphNode::out() method to get the outgoing references for the active drawing but unfortunately it does not include the circular reference. 
I tried the following too, but I am not sure if I am doing it correctly:

1. get the XREFBlockID from the active document using xrefBlockId()

2. Use the blocID in acdbOpenObject() to get AcDbBlockTableRecord, further I can get the BlockTable.I am not sure if this is the right method and what to do next.

Here BAS1, BAS2, BAS3 can be considered as A,B,C.

I am looking for a relevant AutoCAD API that can give me the indication that the drawing is circular.

More specifically my expectation is that I get the link between [the leaf] Drawing1 and [the root] Drawing2 , the circular link.
is there any property that conveys that the drawing had a circular link originally?

[imadHabash]

Hi,

@Nikita_RAUTELA 

as much as i understand (hope so)...

Try from the External Reference palette to use  Tree View (F4)  option. (Upper right)

[pendean]

@Nikita_RAUTELA Would this help you see your content relationships better? Activate it now. Show us the result.

[J-Porter]

In your image you are setting the references up as overlays.  Therefore, you should not have any circular references.  

[Nikita_RAUTELA]

@pendean @J-Porter @imadHabash thanks for the suggestions the result is as follows (but my expectation is not with the UI):

I am developing a program to travel through all the attached references. I am looking for a relevant AutoCAD API that can give me the indication that the drawing is circular.

More specifically my expectation is that I get the link between [the leaf] Drawing1 and [the root] Drawing2 , the circular link.
is there any property that conveys that the drawing had a circular link originally?

[BlackBox_]

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@Nikita_RAUTELA wrote:

I am developing a program to travel through all the attached references. I am looking for a relevant AutoCAD API that can give me the indication that the drawing is circular.

More specifically my expectation is that I get the link between [the leaf] Drawing1 and [the root] Drawing2 , the circular link.
is there any property that conveys that the drawing had a circular link originally?

---

You've not posted any code (in the .NET forum) for the program you're developing, so it's going to be hard for someone to offer advice. 

As a starting point, consider iterating each XREF using ReadDwgFile() with FileOpenMode.OpenForReadAndAllShare, and checking those for an XREF that matches your active document. 

Cheers

[Nikita_RAUTELA]

Currently I am using AcDbXrefGraphNode::out() method to get the outgoing references for the active drawing but unfortunately it does not include the circular reference. 
I tried the following too, but I am not sure if I am doing it correctly:

1. get the XREFBlockID from the active document using xrefBlockId()

2. Use the blocID in acdbOpenObject() to get AcDbBlockTableRecord, further I can get the BlockTable.

I am not sure if this is the right method and what to do next.

I am coding in native(c++) I am not sure if I can set FileOpenMode, but I will explore this as well

[pendean]

@Nikita_RAUTELA As noted by @J-Porter I suspect your core issue is most likely having chosen this type of XREF (which you need to change as that option hides XREFs)

[J-Porter]

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"I am looking for a relevant AutoCAD API that can give me the indication that the drawing is circular."

---

Natively, there is nothing I can think of except the warning you get when you are about to create a circular xref.  And there are even ways to get around that warning.  Outside of that, you don't notice a circular xref until it's too late.  

I wish there was a way to manage control through the reference manager:  https://forums.autodesk.com/t5/civil-3d-ideas/update-request-to-the-reference-manager/idc-p/13724670...

[BlackBox_]

---

@Nikita_RAUTELA wrote:

Currently I am using AcDbXrefGraphNode::out() method to get the outgoing references for the active drawing but unfortunately it does not include the circular reference. 
I tried the following too, but I am not sure if I am doing it correctly:

1. get the XREFBlockID from the active document using xrefBlockId()

2. Use the blocID in acdbOpenObject() to get AcDbBlockTableRecord, further I can get the BlockTable.

I am not sure if this is the right method and what to do next.

I am coding in native(c++) I am not sure if I can set FileOpenMode, but I will explore this as well

---

I understand that you're attempting to identify this within the active document scope - but that is insufficient (even in ARX) - as an XREF in the active document is effectively a copy of the source drawing (and mostly behaves as a block reference). 

An XREF does give you access to its source drawing, which can be opened as a side database - I work in Civil 3D, so I'm relegated to .NET - regardless, you'll need to open the XREFs as side database using AcDbDatabase::readDwgFile() (C++), then query that side DB for it's XREFs, filtering for any that match active document's path, to solve your circular reference query. 

Hope that makes more sense.

[Edit] - Oh! Don't forget to resolve any relative paths.

[Nikita_RAUTELA]

When I perform readDwgFile for the leaf drawing, I am able to get the xRefGraph and eventually its xRefGraphNode(the one I was looking for), but there is an issue while doing this, the status of the xrefNode is unresolved and it does not contain its DB. I tried to access the DB by further getting the BlockID from the xrefGraphNode but the DB there is that of the parent I suppose because the filename in it is that of the leaf drawing only.
Although, I can get the name of the Top Drawing from the leaf, this is still insufficient in my case, as path is not fetchable.
Am I doing something wrong or are the xref opened via readDwgFile's DB always in unresolved state?

[BlackBox_]

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@Nikita_RAUTELA wrote:

When I perform readDwgFile for the leaf drawing, I am able to get the xRefGraph and eventually its xRefGraphNode(the one I was looking for), but there is an issue while doing this, the status of the xrefNode is unresolved and it does not contain its DB. I tried to access the DB by further getting the BlockID from the xrefGraphNode but the DB there is that of the parent I suppose because the filename in it is that of the leaf drawing only.
Although, I can get the name of the Top Drawing from the leaf, this is still insufficient in my case, as path is not fetchable.
Am I doing something wrong or are the xref opened via readDwgFile's DB always in unresolved state?

---

You've not posted any code, so difficult for someone to see where you're stuck. 

Did you store HostApplicationServices.WorkingDatabase, then try {} setting side database current before calling ResolveXrefs() & GetHostDwgXrefGraph(), and finally {} set old database current again?

Never needed to use XrefGraph before, so I'm sure there's a way, but in some test code it was pretty easy to iterate side database's BlockTable to confirm status BlockTableRecord.IsFromExternalReference && !BlockTableRecord.IsFromOverlayReference (since an XREF as attachment is the only real circular reference). The code I have detects the nested circular reference in both B and C - which is technically correct, since they all XREF another as attachment and changing one of them from attachment to overlay would resolve - but will take more work to isolate the culprit to only being C.dwg (with A.dwg open in the editor, that is). 

HTH

                            using (Database sideDb = new Database(false, true))
                            {
                                sideDb.ReadDwgFile(path, FileOpenMode.OpenForReadAndAllShare, false, "");
                                sideDb.CloseInput(true);

                                using (Transaction tr = sideDb.TransactionManager.StartTransaction())
                                {
                                    BlockTable bt = (BlockTable)tr.GetObject(sideDb.BlockTableId, OpenMode.ForRead);
                                    foreach (ObjectId btrId in bt) // <-- replace with linq
                                    {
                                        BlockTableRecord btr = (BlockTableRecord)tr.GetObject(btrId, OpenMode.ForRead);

                                        if (!btr.IsFromExternalReference || btr.IsFromOverlayReference) continue;

                                        ed.WriteMessage($"\n; xref: {btr.PathName}");
                                        if (PathsEqual(btr.PathName.ToUpper(), dwg.ToUpper())) // <-- Normalize paths
                                            ed.WriteMessage($"\n; circular xref found in: {path}");
                                    }
                                    tr.Commit();
                                }
                            }

[Nikita_RAUTELA]

I am suspecting that in your case, the drawing file is not opened in AutoCAD, coming from my observation when I open the drawing file in ACAD it shows a warning that the drawing has circular reference and do you still want to proceed, on proceeding I believe it resolves the circular links and then open the file, thus, I get the isCircularReference api  as  false. 
Nevertheless, I was able to get the filename so i managed to make my use case work, thanks a lot for all the help, much appreciated. I will definitely update if I stumble on some alternative that works.
Bets Regards!