如何在 Firebase 中执行连接查询? [英] How to perform join query in Firebase?

问题描述

在 HashMap 中检索组键后如何执行连接查询，该查询仅显示那些具有该特定用户成员的 grp 详细信息.如果这个结构有问题，请帮我解决这个问题.

After retrieving group key in HashMap how to perform join query which shows only those grp details which have member as that particular user. And if this structure is wrong please help me with this.

结构:

推荐答案

在另一个DatabaseReference中使用DatabaseReference:

 // any way you managed to go the node that has the 'grp_key'
    DatabaseReference MembersRef = FirebaseDatabase.getInstance()
            .getReference()
            .child("Members")
            .child("1CkPG20Tt2dzrVkYkdfCLo")
            .orderByKey().equalTo("-KYnhiAucnasdkadNC")
            .addValueEventListener(
                    new ValueEventListener()
                    {
                        @Override
                        public void onDataChange(DataSnapshot dataSnapshot)
                        {
                            for (DataSnapshot child : dataSnapshot.getChildren())
                            {

                                Map<String, Object> valuesMap = (HashMap<String, Object>) dataSnapshot.getValue();

                                // Get push id value.
                                String key = valuesMap.get("grp_key");


                                // HERE WHAT CORRESPONDS TO JOIN
                                DatabaseReference chatGroupRef = FirebaseDatabase.getInstance().getReference()
                                        .child("Chat_groups")
                                        .orderByKey().equalTo(key)
                                        .addValueEventListener(
                                                new ValueEventListener()
                                                {
                                                    @Override
                                                    public void onDataChange(DataSnapshot dataSnapshot)
                                                    {
                                                        // repeat!!
                                                    }

                                                    @Override
                                                    public void onCancelled(DatabaseError databaseError)
                                                    {

                                                    }
                                                }
                                        )
                            }
                        }

                        @Override
                        public void onCancelled(DatabaseError databaseError)
                        {

                        }
                    }
            );

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