Vue.js Select (Select)下拉(dropdown)选定项 vm 绑定不起作用(bootstrapvue)

我试图创建一个简单的vue，将选中的项目从 Select /下拉列表绑定到vm中的属性.

在使用视图模型中的选项集合时，我无法找到一个清晰简单的例子来说明这一点.

<template>
    <div>
        <h1>Select box</h1>
        <b-dropdown id="ddCommodity"
                    name="ddCommodity"
                    v-model="ddTestVm.ddTestSelectedOption"
                    text="Select Item"
                    variant="primary"
                    class="m-md-2" v-on:change="changeItem">
            <b-dropdown-item disabled value="0">Select an Item</b-dropdown-item>
            <b-dropdown-item v-for="option in ddTestVm.options":selected="option.value == 'LME/ST_TNI_ALL'":value="option.value">{{option.text}}</b-dropdown-item>           
        </b-dropdown> <span>Selected: {{ ddTestVm.ddTestSelectedOption }}</span>
 </div>
</template>


<script>
    export default {
        components: {

        },
        data() {
            return {
                someOtherProperty: null,
                ddTestVm: {
                    originalValue: [],
                    ddTestSelectedOption: "Value1",
                    disabled: false,
                    readonly: false,
                    visible: true,
                    color: "",
                    options: [
                        {
                            "value": "Value1",
                            "text": "Value1Text"
                        },
                        {
                            "value": "Value2",
                            "text": "Value2Text"
                        },
                        {
                            "value": "Value3",
                            "text": "Value3Text"
                        }
                    ]
                }
            }
        },        
        methods: {
            changeItem: async function () {
            //grab some remote data
                try {
                    let response = await this.$http.get('https://www.example.com/api/' + this.ddTestVm.ddTestSelectedOption + '.json');
                    console.log(response.data);
                    this.someOtherProperty = response.data;
                } catch (error) {
                    console.log(error)
                }
            }
        },
        watch: {

        },
        async created() {

        }
    }
</script>

<style>
</style>

无论我try 了什么，我都无法在下拉列表中获取所选值来更改vm的ddTestSelectedOption属性.

有人能在这个问题上提供帮助吗？

谢谢