如何从 firestore 一次获取多个集合组的文档？

Question

So here I Have multiple sub-collections(subjects) in different doc's(grades) and I want to get all the sub-collections(subjects) documents(questions) at once I tried to get them by using Collection group queries the only problem which I am facing in my code sometime it returning all the doc's(questions) but sometimes not what is the issue

this is what i have tried

 const getAllQuestions = (request,response)=>{
    const subjects = ['Maths','English']
    const questionsArray = []
    subjects.forEach((subject,index)=>{
        
     db.collectionGroup(subject)
                       .get()
                       .then((querySnapshot)=>{
                        querySnapshot.forEach((doc) => {
                            questionsArray.push({...doc.data(),id:doc.id})
                        })
                        if(index==subjects.length-1){
                            response.status(200).json({
                                    status:200,
                                    data:questionsArray,
                                    length:questionsArray.length
                          })
                         }
      })
    })
 }

Answer 1

If you don't want to get the subcollections from all grades, but only from one of them, you should not use a collection group query but instead specify the entire path to the collection you want to query/read:

 db.collection('quizQuesDb/Grade 5/'+subject)
                   .get()

If you want to perform a query across all collections of a certain name under a specific path , see: CollectionGroupQuery but limit search to subcollections under a particular document