[Pattern] Adapter - How to make objects work together?

Problem

Imagine you are a skilled Front-end developer who has just finished designing the interface and is only waiting to connect with the API. But on the day the Back-end team says they can't hand it over to you yet, so you have to wait until the API is available before continuing your work.

Or in another scenario, you are assigned the task of integrating the system with a partner through an API. They have provided complete documentation and you only need to connect to the data as described. But near the end, the partner informs you that they have changed the data in some places. You feel frustrated because you have to sit and review and modify code in many places in the project.

The above are two common situations in the work of every programmer. If you have encountered these situations before and felt helpless, this article will introduce a pattern called Adapter to help you overcome this pain to some extent.

Design Pattern - Adapter

Adapter is a structural design pattern that allows incompatible objects with different interfaces to work together.

The Adapter plays a role in converting the data (objects) of one object so that another object can understand it. The Adapter hides the complexity of the conversion process, and the receiving object does not even need to care about the data from the other object, as everything goes through an Adapter.

For example, a chart library only works with data received in JSON format, but the data you fetch from the system is in XML format. In this case, you need to create a function to convert the data from XML to JSON and pass it to the library. This function is called an Adapter.

... -> XML -> Adapter (function) -> JSON -> Library -> ...  

Going back to the problem, once you know about the Adapter, you are no longer completely dependent on the data from the API. What you need to do is to create an object that holds the necessary data for display or processing in the interface, and then create an Adapter function to convert the data from the API into that object, and you're done.

<template>
  <a-list item-layout="horizontal" :data-source="data.list">
    <template #renderItem="{ item }">
      <a-list-item>
        <a-list-item-meta :description="item.description" >
          <template #title>
            <a :href="item.url">{{ item.title }}</a>
          </template>
          <template #avatar>
            <a-avatar :src="item.avatar" />
          </template>
        </a-list-item-meta>
      </a-list-item>
    </template>
  </a-list>
</template>
<script lang="ts">
import { defineComponent, onMounted, reactive } from "vue";

// Data retrieved from the server has the format
// [{
//   tieu_de: "xxx",  
//   mo_ta: "xxx",  
//   anh_dai_dien: "xxx",  
//   lien_ket: "xxx"
// }]
const fetchData = () => {
  return fetch("https://api.example.com/list");
}

// Adapter function that converts data from the API into data
const convertRespToData = (resp: any) => {
  return resp.map((item: any) => {
    return {
      title: item.tieu_de,  
      description: item.mo_ta,  
      avatar: item.anh_dai_dien,  
      url: item.lien_ket
    };
  });
}

export default defineComponent({
  setup() {
    // data is the interface variable to be integrated
    const data = reactive<any>({
      list: [],  
    });

    // Fetch data and integrate into the data variable
    onMounted(() => {
      fetchData().then(resp => {
        data.list = convertRespToData(resp);
      });
    });

    return {
      data,  
    };
  },  
});
</script>

Furthermore, creating and controlling data on the client side will limit the errors that may occur from incompatible data from the API. Instead of directly accepting data from the API and integrating it directly into the interface, it's better to go through an Adapter.

Similarly, for problem 2, we should not overly depend on data from a third-party API. Instead, we should create our own data and write Adapter functions to convert data from them. Avoid receiving and using data directly, as the data they provide may not convey the correct and complete content needed for the system. Therefore, if there is a conversion function in between, it will be easier to handle and detect data-related issues at an early stage.

Adapter has many advantages, but it also has some limitations, such as the need to write more code, and the complexity of the code may increase as the number of Adapters and their interdependencies grow. Therefore, try to organize your code as neatly as possible.

Conclusion

Those were two real-life examples I presented to apply the Adapter pattern in practice, hoping it will be helpful to everyone. Adapter can have different implementations depending on the programming language and the problem being solved. For more details, please click on the reference links below.

References:

• https://refactoring.guru/design-patterns/adapter