How to get a list of nested links for a Revit model using Forge APIs

Question

I can acquire the full list of nested links in a Revit model using Revit APIs by this query:

  FilteredElementCollector collector = new FilteredElementCollector(document);
  return collector.OfCategory(BuiltInCategory.OST_RvtLinks)
    .OfClass(typeof(RevitLinkInstance))
    .Cast<RevitLinkInstance>()
    .Select(linkInstance => document.GetElement(linkInstance.GetTypeId()) as RevitLinkType)
    .Where(revitLinkType => revitLinkType.IsNestedLink)
    .Select(type => type.Name)
    .Distinct()
    .ToList();

I am trying to replicate the same function using Forge APIs. While I can't get the nested links directly, I am hoping to get it in two steps.

First: acquire the list of linked docs, Second: query the linked docs on every linked document acquired in step one.

I am using this API to get the list of linked docs for step one:

'https://developer.api.autodesk.com/data/v1/projects/[project_id]/versions/[version_id]/relationships/refs'

That returns a list that includes: linked docs, the document itself, and any document that has the document linked in. So for example:

If A links B, and B links C, When I call the API on B, I get A, B and C. Now, it's easy to eliminate B from the response, but it's a bit confusing to figure out between A and C which one is a linked document.

I checked all the attributes and couldn't find anything, is there something I am missing? Also, is this the best way to acquire the list of nested linked documents?

Answer 1

Thanks for the response Eason. Ok so if I use the 'GET' equivalent it works as you described. However, I can only get it to work on smaller test models, the API simply returns an empty array for data, even though the project does have several linked document:

{
  "jsonapi": {
    "version": "1.0"
  },
  "links": {
    "self": {
      "href": "https://developer.api.autodesk.com/data/v1/projects/b.19e2199f-4132-4c47-9972-37d4708ea59f/versions/urn:adsk.wipprod:fs.file:vf.ZhP9FgAOTx6T4EV8acbrJg%3Fversion=27/relationships/refs"
    },
    "related": {
      "href": "https://developer.api.autodesk.com/data/v1/projects/b.19e2199f-4132-4c47-9972-37d4708ea59f/versions/urn:adsk.wipprod:fs.file:vf.ZhP9FgAOTx6T4EV8acbrJg%3Fversion=27/refs"
    }
  },
  "data": []
}

Are there any limits for this API? Why would this work on some models and not on the other ones?

Answer 2

To identify which file is the host or link, we can take a look at the direction attribute of the responses of GET projects/:project_id/versions/:version_id/relationships/refs

Here are two example responses representing the host and link correspondingly.

//Host Model
"data": [
    {
        "type": "versions",
        "id": "urn:adsk.wipprod:fs.file:vf.n4QEQGINSWid8VvcBVds1w?version=1",
        "meta": {
            "refType": "xrefs",
            "fromId": "urn:adsk.wipprod:fs.file:vf.n4QEQGINSWid8VvcBVds1w?version=1",
            "fromType": "versions",
            "toId": "urn:adsk.wipprod:fs.file:vf.y6GJ2scBSVSyIRM_wtEsDA?version=1",
            "toType": "versions",
            "direction": "to",
            "extension": {
                "type": "xrefs:autodesk.core:Xref",
                "version": "1.1",
                "schema": {
                    "href": "https://developer.api.autodesk.com/schema/v1/versions/xrefs:autodesk.core:Xref-1.1"
                },
                "data": {
                    "nestedType": "overlay"
                }
            }
        }
    }
],

// Link model
"data": [
    {
        "type": "versions",
        "id": "urn:adsk.wipprod:fs.file:vf.y6GJ2scBSVSyIRM_wtEsDA?version=1",
        "meta": {
            "refType": "xrefs",
            "fromId": "urn:adsk.wipprod:fs.file:vf.n4QEQGINSWid8VvcBVds1w?version=1",
            "fromType": "versions",
            "toId": "urn:adsk.wipprod:fs.file:vf.y6GJ2scBSVSyIRM_wtEsDA?version=1",
            "toType": "versions",
            "direction": "from",
            "extension": {
                "type": "xrefs:autodesk.core:Xref",
                "version": "1.1",
                "schema": {
                    "href": "https://developer.api.autodesk.com/schema/v1/versions/xrefs:autodesk.core:Xref-1.1"
                },
                "data": {
                    "nestedType": "overlay"
                }
            }
        }
    }
],

The direction attribute has two possible values, one is to and another is from.

In the above example, host urn:adsk.wipprod:fs.file:vf.n4QEQGINSWid8VvcBVds1w?version=1 is linked to urn:adsk.wipprod:fs.file:vf.y6GJ2scBSVSyIRM_wtEsDA?version=1. Consider it like an arrow with the head pointing to-wards the link model.

What you see from link model perspective is simply the reverse, the arrow is coming from the host urn:adsk.wipprod:fs.file:vf.n4QEQGINSWid8VvcBVds1w?version=1.

In both example responses, the fromId and toId don't change, only the direction of the arrow depending from which perspective you're looking at.