private fun cacheKeyMethodSpec(): MethodSpec {
  val writeCode = fields
      .map {
        CodeBlock.of("\n+ \"\$L:\$L:\" + this.\$L()", it.type, it.name.decapitalize(), it.name.decapitalize())
      }
      .fold(CodeBlock.builder(), CodeBlock.Builder::add)
      .build()

  val stringCode = CodeBlock.builder()
      .add("return \"\$L{\"\$>\$L\n+ \"}\";\$<\n", objectClassName, writeCode)
      .build()

  return MethodSpec.methodBuilder(CACHE_KEY_PARAM_NAME)
      .addModifiers(Modifier.PUBLIC)
      .returns(String::class.java)
      .addCode(stringCode)
      .build();
}