I got this select code based on vue bootstrap:

```
<b-form-select v-model="selectedgroup" class="mb-3"  @change="searchSubGroup()">
    <option :value="null">Select a group</option>
    <option v-for="group in groupItem" :value="group.id">
        {{group.nome}}
    </option>
</b-form-select>  

```

When the `searchSubGroup()` method is called by @change event, the @change event pass a old value of `selectedgroup`. Example: If i click in option with value = 1 first, the method will call `selectedgroup` as `null`, then if i click again in another option with value = 2, the method will call `selectedgroup` as 1.

```
searchSubGroup(){ 
  this.axios.get("http://chart.solutions/public/api/produto/subgroup/search/" + this.selectedgroup + "/").then(response => {
        if (response.data.erro) {
            //console.log("subgroup doesnt exist")
        }else{
            this.subGroupItem = response.data;
        }
    })
} 

```