SPO Rest API POST - Does not return specified field

Question

I'm on SharePoint Online and I need to use the Rest API to query the Pages library.

Normally, I'd use GET, but since I'm filtering on a Managed Metadata field, I have to use POST instead. For some reason reason, however, I'm not able to get some fields even though I have it on my ViewFields (I'm specifically interested in EncodedAbsUrl or FileRef).

Here's my query:

var query = '<Query><Where><Eq><FieldRef Name="RelatedTag"/><Value Type="TaxonomyFieldType">SomeValue</Value></Eq></Where></Query>';
var viewfields = '<ViewFields><FieldRef name="EncodedAbsUrl" /><FieldRef Name="Title" /></ViewFields>';

$.post({
    url: _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/getByTitle('Pages')/GetItems(query=@v1)?@v1={'ViewXml':'<View>"+query+viewfields+"</View>'}",
    headers: {
        "Accept": "application/json;odata=verbose",
        "Content-Type" : "application/json;odata=verbose",
        "X-RequestDigest": $("#__REQUESTDIGEST").val()
    }
});

The response I get back is this:

As you can see, Title is there, but EncodedAbsUrl isn't. This also does not work if I put in FileRef, FileLeafRef, etc. RelatedTag and all my other custom fields work though.

Answer 1

So I've thought about using a combination of POST and GET requests to the Rest API but found it way too chatty. Instead I looked into JSOM as an alternative and it works:

var clientContext = new SP.ClientContext(_spPageContextInfo.webAbsoluteUrl);
var oList = clientContext.get_web().get_lists().getByTitle('Pages');

var camlQuery = new SP.CamlQuery();
camlQuery.set_viewXml('<View><Query><Where><Eq><FieldRef Name="RelatedTag"/>' +
    '<Value Type="Text">SomeValue</Value></Eq></Where></Query></View>');
this.collListItem = oList.getItems(camlQuery);

clientContext.load(collListItem);

clientContext.executeQueryAsync(function (sender, args) {
    var listItemEnumerator = collListItem.getEnumerator();
    console.log(listItemEnumerator);
    while (listItemEnumerator.moveNext()) {
        var oListItem = listItemEnumerator.get_current();
        console.log('Title: ' + oListItem.get_item('Title') +
            '\nFileRef: ' + oListItem.get_item('FileRef'));
    }
}, null);

Answer 2

Are you trying to get the url of a File? Your query is getting the item, not the file, so you have to $expand=File and then you will have all the Files properties, including FileRef, FileLeafRef and EncodedAbsUrl