How to solve the error of vue modifying the page that the id has no default value?

Vue is a front-end development framework that enables developers to build interactive web applications more efficiently. However, when developing with Vue, you sometimes encounter some problems.

One of them is that when modifying the data on the page, there will be an error that the id does not have a default value. This error is actually easy to fix, and this article will detail how to fix it.

First, let’s take a look at the specific manifestations of this error. In Vue, when we use v-model to bind data, modifying data is a very common operation. For example:

<template>
  <div>
    <input v-model="name">
    <button @click="save">保存</button>
  </div>
</template>

<script>
export default {
  data() {
    return {
      name: ''
    }
  },
  methods: {
    save() {
      // 发送请求保存数据
    }
  }
}
</script>

This code is very simple. We bind a variable name through v-model and bind it to an input element. When we enter content in the input box, the value of name also changes. When we click the "Save" button, we will send a request to the server to save the modified data.

However, when we open the console to view the network request, we will find an error message:

SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'id' cannot be null

This error message tells us that when we sent the request to the server, the server reported A database integrity constraint violation error. Specifically, the server asked us to pass an id value, but we didn't pass this value when sending the request, so the server returned an error.

So, why does this error occur? The root cause of this error is that data bound using v-model does not contain the id field by default. In our example, we only bound a name field, but not the id field.

In order to solve this problem, we need to do two things:

1. Add an id field to the data model;
2. Add a hidden field to our form id field, the value of this field can be obtained from the data returned by the server, so that when we modify the data, the id value can be passed to the server.

Now let’s take a look at how to implement these two steps.

First, we need to add the id field to the data model. Add an id field to Vue's data, like this:

data() {
  return {
    id: null, // 默认值为null，因为在创建新对象时可能还没有id
    name: ''
  }
}

Then, add a hidden id field to our form:

<template>
  <div>
    <input v-model="name">
    <input type="hidden" v-model="id">
    <button @click="save">保存</button>
  </div>
</template>

Note that we set the id field type="hidden" so it doesn't show up on the page. We bind the value of the id field to a hidden input element so that the id value can be passed to the server when sending a request.

Now, let’s modify the save method and pass the id value to the server:

save() {
  // 发送请求保存数据
  const data = {
    id: this.id,
    name: this.name
  }
  axios.post('/api/save', data).then(response => {
    // 处理成功
  }).catch(error => {
    // 处理失败
  })
}

Now, we have successfully solved this problem. We can modify the data normally and no longer encounter the error that the id has no default value.

To summarize, when we use the Vue framework for development, we sometimes encounter some strange errors. In this article, we learned how to resolve the id has no default value error encountered while saving data. We found that the root cause of this error was that we did not define the id field in the data model. We were able to solve this problem by adding an id field and binding it to a hidden input element.

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