Retrieving Multiple SharePoint Managed Metadata Columns via REST

I’ve used this code a few times in different project now, and I wanted to post it in case it’s useful for anyone. Most of us know that the REST APIs still have some weaknesses, and working with Managed Metadata is definitely one of them. (See: Let’s Capture Missing or Insufficient SharePoint REST Endpoints)

If you have a couple Managed Metadata columns in your list and you just retrieve the columns in REST like so…

request: {
  method: "GET",
  url: _spPageContextInfo.siteServerRelativeUrl +
      "/_api/web/lists/getbytitle('ListName')/items?" +
      "$select=ID,Title," +
      "MyLocation,MyDepartment" +
      "&$top=5000",
  headers: {
      "Accept": "application/json; odata=nometadata"
  }
}

…you’ll get back data like this:

{
    "Id": 5,
    "ID": 5,
    "Title": "Item Title",
    "MyDepartment": {
        "Label": "6",
        "TermGuid": "748ca38e-9cea-488f-9a9a-6a20f6dff80a",
        "WssId": 6
    },
    "MyLocation": {
        "Label": "5",
        "TermGuid": "c8cb412b-ed99-4034-8ca7-5019940ec354",
        "WssId": 5
    },
}

That’s not very helpful at all, since we don’t get the Term itself, just some gobbledy-gook pointers and a GUID. What we really want is the text for the term.

I found a useful thread on SharePoint StackExchange. As is so often the case, Mikael Svenson (@mikaelsvenson) had posted an answer which helped a lot. (We need more Mikael!)

You can do a workaround using the TaxCatchAll field as long as you know which terms belong to which taxonomy field – if you have multiple.

Looking into this, retrieving the TaxCatchAll column was indeed the way to go. By including it in my REST calls, and requesting both the Term and the ID, I could get the text values for the Managed Metadata (aka Taxonomy, aka Term Set-based – seriously, Microsoft???) columns in my list and make sense of them.

At the most basic level, this looks something like this:

request: {
  method: "GET",
  url: _spPageContextInfo.siteServerRelativeUrl +
      "/_api/web/lists/getbytitle('ListName')/items?" +
      "$select=ID,Title," +
      "MyLocation,MyDepartment," +
      "TaxCatchAll/ID,TaxCatchAll/Term," +
      "&$expand=TaxCatchAll" +
      "&$top=5000",
  headers: {
      "Accept": "application/json; odata=nometadata"
  }
}

This “expands” the Managed Metadata columns, returning the text for the terms. But don’t get too excited too fast! We gain the term text, but lose something else (of course!). The data you get back looks something like this:

{
    "Id": 5,
    "ID": 5,
    "Title": "Item Title",
    "TaxCatchAll": [{
        "ID": 5,
        "Term": "Lab 2B"
    }, {
        "ID": 6,
        "Term": "Histology"
    }],
    "MyDepartment": {
        "Label": "6",
        "TermGuid": "748ca38e-9cea-488f-9a9a-6a20f6dff80a",
        "WssId": 6
    },
    "MyLocation": {
        "Label": "5",
        "TermGuid": "c8cb412b-ed99-4034-8ca7-5019940ec354",
        "WssId": 5
    },
}

So we have the text for the terms, but we basically lose the ability to know which is which. Or do we?

When we request the TaxCatchAll/ID property, we get the ID property which ties everything together, though you probably won’t find much documentation on this anywhere. In my example above, the value with ID=5 matches WssId=5 and so on.

I couldn’t find a post anywhere with code that tied all this together, so here we are. I’ve written a little function you can call to get the right values easily called getTaxonomyValue. You call it like this:

getTaxonomyValue(obj, "MyLocation")

…where:

• obj = the row of data (stored as an object in JSON),
• fieldName = the name of the column for which you want to grab the term text

Note that I make almost all my REST calls with odata=nometadata these days to reduce the payloads as much as possible; I haven’t tested this with the other variants.

function getTaxonomyValue(obj, fieldName) {

  // Iterate over the fields in the row of data
  for (var field in obj) {
      // If it's the field we're interested in....
      if (obj.hasOwnProperty(field) && field === fieldName) {
          if (obj[field] !== null) {
              // ... get the WssId from the field ...
              var thisId = obj[field].WssId;
              // ... and loop through the TaxCatchAll data to find the matching Term
              for (var i = 0; i < obj.TaxCatchAll.length; i++) {
                  if (obj.TaxCatchAll[i].ID === thisId) {
                      // Augment the fieldName object with the Term value
                      obj[field].Term = obj.TaxCatchAll[i].Term;
                      return obj[field];
                  }
              }
          }
      }
  }
  // No luck, so return null
  return null;

}

Calling this function matches the WssID and ID values within the object and returns the value you actually want.

References

• Workaround to filter on taxonomy columns using OData filters instead of CAML using REST in SharePoint by Mikael Svenson
• Can I use $expand to get Managed Metadata column values? at StackOverflow

by Marc D Anderson via Marc D Anderson's Blog