cloudfirestore how to get data code example

Example 1: document.set() firebasefirestore java

var washingtonRef = db.collection("cities").doc("DC");// Atomically add a new region to the "regions" array field.washingtonRef.update({    regions: firebase.firestore.FieldValue.arrayUnion("greater_virginia")});// Atomically remove a region from the "regions" array field.washingtonRef.update({    regions: firebase.firestore.FieldValue.arrayRemove("east_coast")});

Example 2: document.set() firebasefirestore java

// Create an initial document to update.var frankDocRef = db.collection("users").doc("frank");frankDocRef.set({    name: "Frank",    favorites: { food: "Pizza", color: "Blue", subject: "recess" },    age: 12});// To update age and favorite color:db.collection("users").doc("frank").update({    "age": 13,    "favorites.color": "Red"});