遍历子集合和文档-angularfirestore

Question

在尝试从Firestore访问子集合时，我在数据变量中拥有所有值，当我尝试打印值时，出现错误InvalidPipeArgument：'[object Object]'for pipe'AsyncPipe'

下面的代码段中的“数据”具有以下值

[
    {
        "_id": "5c21d780f82aa31334ab6506",
        "billingHours": [
            {
                "_id": null,
                "totalHours": 16
            }
        ]
    },
    {
        "_id": "5c21d780f82aa31334ab6507",
        "billingHours": [
            {
                "_id": null,
                "totalHours": 16
            }
        ]
    }
]

在我的html代码中，我尝试打印ID“游泳池”的值

      data:{
      "Kids Pool":           
     {"Chlorine":"Present","Color":"Nil","Turbidity":"Nil","pH":"Neutral"},
     "Main Pool": 
      {"Chlorine":"Nil","Color":"Green","Turbidity":"Yes","pH":"7"},
      "id":"Swimming Pool"}

   this.dieselGeneratorCollections = 
   this.afs.collection('apartments/1001- 
   SJR Verity/Daily Readings');  
   this.posts = this.dieselGeneratorCollections.valueChanges();
   this.dailyReadings = 
   this.dieselGeneratorCollections.snapshotChanges().pipe(
    map(actions => {
      return actions.map(a => {
        const data = a.payload.doc.data() as any;
         data.id = a.payload.doc.id;
         console.log("data:"+JSON.stringify(data) );
        return data; 
      });
    }));

如何打印“ swimmingPool”的值