谁能告诉我在这种情况下我哪里错了？

Question

我试图限制如果程序名称已经存在并且连接值不存在，则推送连接值，否则什么都不做，但我的连接值将被推入数据库。

这是代码：

public void addProgramAndDepartmentName(String programName, String departmentName) {    
    final DatabaseReference rootRef;
    rootRef = FirebaseDatabase.getInstance().getReference();

    String programAndDepartmentName = programName + departmentName;

    rootRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            if ( !(snapshot.child("Program & Departments").child(programName).exists()) ) {    
                rootRef.child("Program & Departments").child(programName).push().child("Program Name").setValue(programAndDepartmentName).addOnCompleteListener(new OnCompleteListener<Void>() {
                    @Override
                    public void onComplete(@NonNull Task<Void> task) {
                        /*AddCourses addProgramNameToSpinnerInAddCourse = new AddCourses();
                        addProgramNameToSpinnerInAddCourse.getDataIntoSpinnerFromFirebase();
                        addProgramNameToSpinnerInAddCourse.spinnerArrayAdapter.notifyDataSetChanged();*/

                        if (!task.isSuccessful()) {    
                            Toast.makeText(AddPrograms.this, "Program and Department is not Added into Database.", Toast.LENGTH_SHORT).show();

                        }    
                        else {    
                            Toast.makeText(AddPrograms.this, "Program and Department name is added into Database if.", Toast.LENGTH_SHORT).show();
                            loadingBar.dismiss();    
                        }
                    }
                });
            }
            else if( (snapshot.child("Program & Departments").child(programName).exists() ) &&
                    ( !( snapshot.child("Program & Departments").child(programName).child("Program Name").child(programAndDepartmentName).exists() ) ) ) {
                rootRef.child("Program & Departments").child(programName).push().child("Program Name").setValue(programAndDepartmentName).addOnCompleteListener(new OnCompleteListener<Void>() {
                    @Override
                    public void onComplete(@NonNull Task<Void> task)  {    
                        /*AddCourses addProgramNameToSpinnerInAddCourse = new AddCourses();
                        addProgramNameToSpinnerInAddCourse.getDataIntoSpinnerFromFirebase();
                        addProgramNameToSpinnerInAddCourse.spinnerArrayAdapter.notifyDataSetChanged();*/

                        if (!task.isSuccessful()) {

                            Toast.makeText(AddPrograms.this, "Program and Department is not Added into Database.", Toast.LENGTH_SHORT).show();

                        }    
                        else {    
                            Toast.makeText(AddPrograms.this, "Program and Department name is added into Database else if.", Toast.LENGTH_SHORT).show();
                            loadingBar.dismiss();    
                        }
                    }
                });
            }    
            else {    
                Toast.makeText(AddPrograms.this, "This " + programName + " already Exists.", Toast.LENGTH_SHORT).show();
                loadingBar.dismiss();    
            }

        }

        @Override
        public void onCancelled(@NonNull DatabaseError error) {    
        }
    });    
}

但唯一正常工作的条件是第一个条件是 And is not working

这是我的 JSON 文件：

{
  "Program & Departments" : {
    "Bs" : {
      "-MV4Heye6EkKPMFlL9IX" : {
        "Program Name" : "Bscs"
      },
      "-MV4Hfy_MHv0CVCnlsRZ" : {
        "Program Name" : "Bscs"
      }
    }
  }
}

请指导我哪里错了？

Answer 1

如果您希望存在具有特定值的单个节点，请将该值作为该节点的键：

{
  "Program & Departments" : {
    "Bs" : {
      "Bscs": true
    }
  }
}

使用这种结构，路径/Program & Departments/Bs/Bscs保证只存在一次，因为 JSON 只能包含该路径一次。

然后，您可以使用单个事务检查路径是否存在，如果不存在则创建它：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = rootRef.child(programName).child(programAndDepartmentName);
ref.runTransaction(new Transaction.Handler() {
    @Override
    public Transaction.Result doTransaction(MutableData mutableData) {
        if (!mutableData.exists())
            mutableData.setValue(true);
        }
        return Transaction.success(mutableData)
    }

    @Override
    public void onComplete(DatabaseError databaseError, boolean committed, DataSnapshot currentData) {
        Log.d(TAG, "runTransaction:" + databaseError);
    }
});