求助！<unicloud-db>嵌套联表怎么实现啊

三张表学校、班级、学员做foreignKey关联下怎么用<unicloud-db>从学员里取出学校名称啊

错误的代码

<template>  
    <unicloud-db collection="test-student,test-class,test-school" field="class_id._id.name,class_id.name,name"  
        v-slot:default="{data, loading, error, options}">  
        <view v-for="(item,index) in data" :key="index">  
            <text>{{item.class_id[0]._id[0].name}}</text><!-- field不能副表再关联，不支持这种写法，应该怎么办呢 -->  
            <text>{{item.class_id[0].name}}</text>  
        </view>  
    </unicloud-db>  
</template>

表

{  
    "_id": {  
        "description": "存储文档 ID，系统自动生成"  
    },  
    "name": {  
        "bsonType": "string",  
        "description": "学校名称",  
        "trim": "both",  
        "title": "学校名称"  
    }  
},   
{  
    "_id": {  
        "description": "存储文档 ID，系统自动生成"  
    },  
    "school_id": {  
        "bsonType": "string",  
        "title": "所属学校",  
        "description": "所属学校 id，参考`test-school`表",  
        "foreignKey": "test-school._id"  
    },  
    "name": {  
        "bsonType": "string",  
        "description": "班级名称",  
        "trim": "both",  
        "title": "班级名称"  
    }  
},   
{  
    "_id": {  
        "description": "存储文档 ID，系统自动生成"  
    },  
    "class_id": {  
        "bsonType": "string",  
        "title": "所属班级",  
        "description": "所属班级 id，参考`test-class`表",  
        "foreignKey": "test-class._id"  
    },  
    "name": {  
        "bsonType": "string",  
        "description": "学员姓名",  
        "trim": "both",  
        "title": "学员姓名"  
    }  
}