getValues (params) {
    const source = Vue.axios.CancelToken.source();

    const promise = new Promise((resolve, reject) => {
      const options = { params, cancelToken: source.token };

      Vue.axios.get('api/unique', options)
        .then((response) => {
          resolve(response.data);
        })
        .catch((error) => {
          if (!Vue.axios.isCancel(error)) {
            reject(error);
          }
        });
    });

    return { promise, source };
  }
Gets field values from the server
@param {Object} params The parameters to send with the query
@returns {Object} { promise, source } An object including a promise object
that signals the completion or rejection of the request and a source object
to allow the request to be cancelled