Firebase

• Official Docs

• SQL vs Firebase DB

Realtime DB (For Web)

• Is a single JSON object

• Use Firebase SDK (platform-specific) to interface with database: const db = firebase.database().ref()

• Get a reference to a node (key): const ref = db.child("path/to/ref")

• To retrieve data in real-time, add event listeners like so:

  // value events work best for syncing objects
  objectRef.on("value", snap => {...})
  
  // child events work best for lists
  listRef.on("child_added", snap => {...})
  
  // Use ref.off to stop listening
  const handle = ref.on("value", ...)
  objectRef.off("value", handle)

  • EVENTS

    • value
    • once
    • child_added
    • child_removed
    • child_changed
    • child_moved

• To query data, the syntax is usually reference().order().query1().query2()...on(), like so:

  ref.orderByChild("someKey").equalTo("someValue").limitToFirst(1).on(...)

  • ORDER

    • orderByKey() // eg paging
    • orderByChild() // eg where clause in SQL
    • orderByValue() // eg numeric sorting

  • QUERY

    • startAt() // range start
    • endAt() // range end, use with startAt for unicode support (see eg below)
    • equalTo()
    • limitToFirst()
    • limitToLast()
    • startAfter()
    • endBefore()

  // Example node
  // "users": {
  //     "1": {
  //         "name": "abc",
  //         "age": 123
  //       }, ...
  //   }
  
  // Get all "users" that have "name" starting with "X"
  ref.child("users").orderByChild("name").startAt("X").endAt("X\uf8ff");
  
  // Get all users whose age is less than 100
  ref.child("users").orderByChild("age").endAt(99);

• Multipath (ATOMIC) Update

  // for updateObject like
  const updateObject = {
    "path/to/ref/1/key": "newValue",
    "path/to/another/ref/key": "newValue",
    "path/to/one/more/ref/key": "newValue",
  };
  
  // Update all values (starting from root) at once (or fail together)
  rootRef.update(updateObject);

• Security Rules

  • A JSON file separate from DB

    {
      "rules": {
        "some/ref": {
          "$childKey": {
            ".read": true,
            ".write": true,
            ".validate": true
          }
        }
      }
    }

    • Use server variables to construct rules:

      • Auth
      • Data
      • New Data (inside .write and .validate)
      • Now (timestamp)
      • Root
      • $wildcards

      // Users can only see/modify their own data, where their name must be a string
      {
        "rules": {
          "users": {
            "$uid": {
              ".read": "auth.uid == $uid",
              ".write": "auth.uid == $uid"
              ".validate": "newData.child('name').isString()"
            }
          }
        }
      }