BelongsTo Required relation Mixin in loopback NodeJs

RequiredRelation.js

'use strict';
let _ = require('lodash');

module.exports = function(Model, options) {
  Model.observe('before save', checkBelongsToIntegrity);
};

let checkBelongsToIntegrity = function(ctx, next) {
  if (ctx.instance) {
    let Model = ctx.Model;
    let msg = '';
    let promiseArray = [];

    let relationsArray = relationsArrayData(ctx);
    relationsArray.forEach(function(relation) {
      if (relation.type == 'belongsTo') {
        let parentModelName = relation.modelName;
        let parentModel = Model.app.models[parentModelName];
        let parentId = '';
        let keyName = parentModelName.charAt(0).toLowerCase() + parentModelName.slice(1) + 'Id';
        if (relation.fk) {
          parentId = ctx.instance[relation.fk];
        } else {
          parentId = ctx.instance[keyName];
        }
        if (parentId) {
          if (parentId != 0) {
            promiseArray.push(parentModel.findById(parentId).then(function(parentInstance) {
              if (parentInstance === null) {
                msg += 'No ' + parentModelName + ' with "' + parentId + '" id. ';
              }
            }));
          } else {
            msg += 'No ' + parentModelName + ' with "' + parentId + '" id. ';
            promiseArray.push(msg);
          }
        } else if (relation.fkReq == true) {
          msg += parentModelName + ' Id is required.';
          promiseArray.push(msg);
        } else {
          if (parentId == 0) {
            msg += 'No ' + parentModelName + ' with "' + parentId + '" id. ';
            promiseArray.push(msg);
          }
        }
      }
    });
    if (promiseArray.length > 0) {
      Promise.all(promiseArray).then(function() {
        next(msg);
      }, console.error).catch(function(err) {
        next(err);
      });
    } else {
      next();
    }
  } else {
    next();
  }
};

let relationsArrayData = function(ctx) {
  let relations = ctx.Model.definition.settings.relations;
  let relationsArray = _.map(relations, rel => {
    return {modelName: rel.model,
      fkReq: rel.foreignKeyRequired, fk: rel.foreignKey, type: rel.type};
  });
  return relationsArray;
};