如何使用Kotlin更深入地使用属性查询Firestore集合? [英] How to query a Firestore collection using a property from a step deeper with Kotlin?

问题描述

我有一个Cloud Firestore数据库用于运输:

I have a Cloud Firestore database for transportations:

• 交通运输{collection}
  • TransportationId {文档}
    • TransportationName:私人运输"
    • 汽车{收藏}
      • CarId {document}
        • CarName:出租车"
        • Transportations {collection}
          • TransportationId {document}
            • TransportationName: "Private Transaportation"
            • Cars {collection}
              • CarId {document}
                • CarName: "Taxi"
                • 汽车名称:私人出租车"

                在Cars集合中，我有100余辆汽车(文档).我在文档中或在stackoverflow上都找不到如何获取CarName名称具有特定特定值的所有运输名称的方法.该如何解决?

                In Cars collection I have over 100 cars (documents). I cannot find in the documentation nor on stackoverflow how to get all the transportation names in which the CarName name has a specific particular value. How to solve this?

                val Taxi = db
                    .collection("Transportations").document("TransportationId")
                    .collection("Cars").whereEqualTo("CarName", "Private Taxi")
                

                谢谢！

                推荐答案

                简短的答案是您无法在Firestore中实现这一目标.无论包含哪种交通工具，都无法在数据库中查询所有汽车.

                The short answer is that you cannot achieve this in Firestore. You cannot query your database for all the cars regardless of which transportation contained them.

                但是在这种情况下，有一种解决方法，您应该通过创建一个名为cars的新顶级集合来稍微更改数据库结构，并在其中添加所有car对象.在每个car对象之外，您还应该添加所需的transportation作为属性.这样，您就可以根据需要查询数据库.

                But in such cases, there is a workaround in which you should change your database structure a little bit by creating a new top-level collection named cars in which you should add all your car objects. Beheath each car object you'll also should add the desired transportation as a property. In this way you'll be able to query the database according to your needes.

                您的数据库结构应如下所示:

                Your database structure should look like this:

                Firestore-root
                   |
                   --- cars (collection)
                        |
                        --- carId (document)
                              |
                              --- transportation: "Private Taxi"
                              |
                              --- //other car details
                

                这篇关于如何使用Kotlin更深入地使用属性查询Firestore集合?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！