How to add values to Firebase Firestore without overwriting?

Question

I have two Activities, I am adding data to Firestore from these two activities individually. But, whenever I add second activity data to Firestore, it is overwriting the fir

Answer 1

Try this for a direct update

db.collection('cities').doc('restaurants').update({ rating:"3.2" });

Only the field rating is going to change, the rest of the fields will remain the same.

Lets say you have 3 fields, and want to change only 2 of them, you can also do this in a different way

// You get the document 'restaurants' and then do the below
db.collection('cities').doc('restaurants').get().then((doc) => {

    // Get the rating field string, parse it to a float, remove 0.4 from it and
    // set it to a tmp variable
    var tmpRating = parseFloat(doc.data()['rating']) - 0.4;

    // Get the array of strings field 'menu' and set it to a tmp variable
    var tmpMenu = doc.data()['menu'];

    // Push 'spaghetti' string to the tmp array of strings( Can also put an
    // adapting string variable instead of a specific string like 'spaghetti'
    tmpMenu.push('spaghetti');

    // Update only the specific fields 'rating' and 'menu' and keep the rest unchanged.
    db.collection('cities').doc(doc.id).update({
        rating: toString(tmpRating), // Don't forget to separate them by commas
        menu: tmpMenu
    });
});