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Configure the cascading DropDownList

The cascading DropDownList is a series of DropDownList, where the value of one DropDownList depends upon another’s value. This can be configured by using the change event of the parent DropDownList. Within that change event handler, data has to be loaded to the child DropDownList based on the selected value of the parent DropDownList.

The following example, shows the cascade behavior of country, state, and city DropDownList. Here, the dataBind method is used to reflect the property changes immediately to the DropDownList.

Source
Preview
app.vue
<template>
  <div id="app">
    <div id='container' style="margin:50px auto 0; width:250px;">
        <br>
          <ejs-dropdownlist id='countries' ref='countries' :query='Query1' :dataSource='countryData' :index='countryindex' :fields='countryfields' :change='onCountryChange' placeholder='Select a country'></ejs-dropdownlist>
        <div class="padding-top">
          <ejs-dropdownlist id='states' ref='states' :query='Query2' :dataSource='stateData' :index='stateindex' :fields='statefields' :enabled='stateenabled' :change='onStateChange' placeholder='Select a state'></ejs-dropdownlist>
        </div>
        <div class="padding-top">
          <ejs-dropdownlist id='cities' ref='cities' :query='Query3' :dataSource='cityData' :index='cityindex' :enabled='cityenabled' :fields='cityfields' placeholder='Select a city'></ejs-dropdownlist>
        </div>
    </div>
  </div>
</template>
<script>
import Vue from 'vue';
import { DropDownListPlugin } from "@syncfusion/ej2-vue-dropdowns";
Vue.use(DropDownListPlugin);
import { Query } from '@syncfusion/ej2-data';

export default {
  data () {
    return {
      countryData: [
        { CountryName: 'United States', CountryId: '1' },
        { CountryName: 'Australia', CountryId: '2' }
      ],
      stateData: [
        { StateName: 'New York', CountryId: '1', StateId: '101' },
        { StateName: 'Virginia ', CountryId: '1', StateId: '102' },
        { StateName: 'Tasmania ', CountryId: '2', StateId: '105' }
      ],
      cityData : [
        { CityName: 'Albany', StateId: '101', CityId: 201 },
        { CityName: 'Beacon ', StateId: '101', CityId: 202 },
        { CityName: 'Emporia', StateId: '102', CityId: 206 },
        { CityName: 'Hampton ', StateId: '102', CityId: 205 },
        { CityName: 'Hobart', StateId: '105', CityId: 213 },
        { CityName: 'Launceston ', StateId: '105', CityId: 214 }
      ],
      countryfields : { value: 'CountryId', text: 'CountryName' },
      statefields : { value: 'StateId', text: 'StateName' },
      cityfields : { text: 'CityName', value: 'CityId' },
      countryindex : 1,
      stateindex : 0,
      cityindex : 0,
      cityenabled : false,
      stateenabled : false,
      Query1: null,
      Query2: null,
      Query3: null
    }
  },
  methods: {
        onCountryChange: function(e) {
            this.Query2 = new Query().where('CountryId', 'equal', this.$refs.countries.ej2Instances.value);
            this.stateenabled = true;
        },
        onStateChange: function(e) {
            this.Query3 = new Query().where('StateId', 'equal', this.$refs.states.ej2Instances.value);
            this.cityenabled = true;
        }
    }
}
</script>
<style>
@import "../../node_modules/@syncfusion/ej2-base/styles/material.css";
@import "../../node_modules/@syncfusion/ej2-inputs/styles/material.css";
@import "../../node_modules/@syncfusion/ej2-vue-dropdowns/styles/material.css";
  #container .padding-top {
    padding-top: 35px;
}
</style>