Question

我们正在将应用程序从Parse迁移到Firebase，我想建立一个用户界面，我可以从以下Firebase数据结构中显示学生姓名以及他/她所属的教室。例如，aluck的课堂名称为10th Grade。

{
    "students": {
        "aluck": {
            "firstName": "Andrew",
            "lastName": "Luck",
            "classroom": "-KJlJhyNH6ImKke-qAd-"
        },
        "bmorino": {
            "firstName": "Beth",
            "lastName": "Morino",
            "classroom": "-KJlJhyNH6ImKke-qAd-"
        }
    },
    "classRooms": {
        "-KJlJhyNH6ImKke-qAd-": {
            "location": "Down stairs",
            "name": "10th Grade",
            "students": {
                "aluck": true,
                "bmorino": true,
            }
        }
    }
}

我的假设是当我使用Firebase JavaScript SDK执行此类操作时

var db = firebase.database(); 
db.ref("students/aluck").on("value", function(snap) { 
    // success method will expose the classroom object with it 
});

它将公开classRooms对象，但它不会。

在Parse中，我能够做到

var query = new Parse.Query(Student);
query.include("ClassRoom");

并且它会公开Student和ClassRoom个对象。

感谢任何帮助。

Answer 1

Firebase数据库不支持自动加入学生和教室。您必须使用自己的代码处理此问题。

var db = firebase.database(); 
db.ref("students/aluck").on("child_added", function(student) { 
    db.ref("classRooms").child(student.child("classroom").val()).once("value", function(classroom) {
        console.log(classroom.val());
    });
});

如果您担心此类once来电的效果，请参阅：Speed up fetching posts for my social network app by using query instead of observing a single event repeatedly

从多对多结构中检索数据与Prase query.include类似

1 个答案: