How to add values in database-CodePudding

I have got a projeect with react native. It counst trains of user: Also, when the user make regisration, it takes the standart value - 0:

          set(ref(db, 'users/'   res.data.localId), {          
            email: email,
            countTrains: 0
          }).then(() => {
             console.log('Made new account');    
        })  
            .catch((error) => {
                console.log(error);
            });

And when i try to add a new value into my countTrains variable:

update(ref(db, 'users/'   user.localId), {       
      countTrains:  countTrain, // may the mistake is here
    }).then(() => {
      console.log('Обновление бд');    
  })  
      .catch((error) => {
          alert(error);
      });

But if a make a logout and takes it again, my value becomes to again 1:

I need to add value like 4 1, and in the firebase should be 5

CodePudding user response：

To increment a value in the database, use the atomic increment operator:

update(ref(db, 'users/'   user.localId), {       
  countTrains: firebase.database.ServerValue.increment(4);
})