Is it possible to update Managed Metadata site column using REST API / SharePoint Web Service?

Question

I am having a requirement where I need to update the Managed Metadata column value using REST API or SharePoint Web Service.

I have gone through this and this and this post but this won't help me because I am not having Term Guid.

What I have is only Term Label. So I want to know is there REST / SharePoint Web Service example using which I can set value in my Managed Metadata column value?

Again! I am not having SharePoint Environment to work, so CSOM, JSOM and SSOM will won't work for me.

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Update : I somehow managed to get TermGuid by TermName using SharePoint Taxonomy Web Service. Now I am having TermGuid, Label and I tried but still I am not able to update the field value.

Here is my code which I am using to update the Managed Metadata field.

var digest = GetFormDigest();
if (!string.IsNullOrEmpty(digest))
{
    var url = siteUrl + "_api/Web/GetFileByServerRelativeUrl('/" + libraryName + "/" + fileName + "')/ListItemAllFields";
    var body = "{ '__metadata' : {'type': 'SP.Data.ListNameListItem},'FieldName' : { '__metadata' : {'type': 'SP.Taxonomy.TaxonomyFieldValue'},'Label': 'TermLabel','TermGuid':'TermGuid','WssId': -1 } } ";
    var client = new WebClient();
    client.Credentials = creds;
    client.Headers[HttpRequestHeader.Accept] = "application/json;odata=verbose";
    client.Headers[HttpRequestHeader.ContentType] = "application/json;odata=verbose";
    client.Headers["X-RequestDigest"] = digest;
    client.Headers["IF-MATCH"] = "*";
    client.Headers["X-Http-Method"] = "MERGE";
    var json = client.UploadString(url, body);
}

I am following this post now. I crossed checked for internal name, my internal name is 100% correct for MMD field

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Update

I again somehow managed the code with SharePoint List Web Service Method from this post. The code I used is as follow:

Lists list = new Lists();
list.Credentials = creds;
XmlNode ndListView = list.GetListAndView(libraryName, "");
string strListID = ndListView.ChildNodes[0].Attributes["Name"].Value;
string strViewID = ndListView.ChildNodes[1].Attributes["Name"].Value;
XmlDocument docNew = new XmlDocument();
XmlElement batchElement = docNew.CreateElement("Batch");
batchElement.SetAttribute("OnError", "Return");
batchElement.SetAttribute("ListVersion", "1");
batchElement.SetAttribute("ViewName", strViewID);
batchElement.InnerXml = "<Method ID='1' Cmd='Update'>" +
"<Field Name='ID'>2</Field>" +
"<Field Name='Title'>Modified through lists.asmx</Field>" +
"<Field Name='City'>" + termValue + "</Field></Method>";
XmlNode ndResult;
try
{
       ndResult = list.UpdateListItems(strListID, batchElement);
}
catch (Exception soapException)
{
}

Where City is my MMD fields internal Name and termValue : "-1;#TermName|TermGuid"

Still the Non Managed Metadata fields got updated but MMD field does not. Any kind of help and suggestion are appreciated.

Answer 1

The problem for you is that you only have Term Label and Term Guid is not available. There is no REST API support for term store yet, so you cannot query the termset and get the guid for the Term Label.

If you are looking for C# CSOM code to update taxonomy field value see this Post