code: function injectForeignFields(targetEntity) {
          switch (type) {
              case '1:1':
                  return entityModifier.readEntityProperty(targetEntity, 'fields').then(function(fields) {
                      fields.push(entity.primary);
                      entityModifier.modifyEntityProperty(targetEntity, 'fields', JSON.stringify(fields));
                      return targetEntity;
                  });
              case '1:many':
                  break;
              case 'many:1':
                  return entityModifier.readEntityProperty(targetEntity, 'fields').then(function(fields) {
                      fields.push(entity.primary);
                      entityModifier.modifyEntityProperty(targetEntity, 'fields', JSON.stringify(fields));
                      return targetEntity;
                  });
              case 'many:many':
                  break;
          }
      }
docs: - find foreign entities to modify
  - inject foreign keys where needed
  - output changes to foreign entity