getForeignKey() {
    // we reuse identifierCache because it's the same logic as get identifier
    if (typeof identifierCache[this.name] !== "string") {
      const foreignKey = `${camelize(this.name)}Id`;

      identifierCache[this.name] = foreignKey;
    }

    return identifierCache[this.name];
  }
@method getForeignKey
@return {String} Foreign key for the association
@public