Example code for Firebase related operations-JS Tutorial-php.cn

今天需要对 Firebase 增加删除功能，代码精简如下：

Firebase 修改节点：

Firebase 监听：

var signaturesRef = defaultApp.database().ref('signatures');

signaturesRef.orderByChild("isChecked").equalTo(false).on("child_added", function(snapshot, prevChildKey) { // TODO: });

admin.database.DataSnapshot

>> key

// Assume we have the following data in the Database:{ "name": { "first": "Ada", "last": "Lovelace"
}
}var ref = admin.database().ref("users/ada");
ref.once("value")
.then(function(snapshot) { var key = snapshot.key; // "ada"
var childKey = snapshot.child("name/last").key; // "last"
});

>> child

var rootRef = admin.database().ref();
rootRef.once("value")
.then(function(snapshot) { var key = snapshot.key; // null
var childKey = snapshot.child("users/ada").key; // "ada"
});

>> exists

// Assume we have the following data in the Database:{ "name": { "first": "Ada", "last": "Lovelace"
}
}// Test for the existence of certain keys within a DataSnapshotvar ref = admin.database().ref("users/ada");
ref.once("value")
.then(function(snapshot) { var a = snapshot.exists(); // true
var b = snapshot.child("name").exists(); // true
var c = snapshot.child("name/first").exists(); // true
var d = snapshot.child("name/middle").exists(); // false
});

>> foreach

// Assume we have the following data in the Database:{ "users": { "ada": { "first": "Ada", "last": "Lovelace"
}, "alan": { "first": "Alan", "last": "Turing"
}
}
}// Loop through users in order with the forEach() method. The callback// provided to forEach() will be called synchronously with a DataSnapshot// for each child:var query = admin.database().ref("users").orderByKey();
query.once("value")
.then(function(snapshot) {
snapshot.forEach(function(childSnapshot) { // key will be "ada" the first time and "alan" the second time
var key = childSnapshot.key; // childData will be the actual contents of the child
var childData = childSnapshot.val();
});
});

>> hasChildren

// Assume we have the following data in the Database:{ "name": { "first": "Ada", "last": "Lovelace"
}
}var ref = admin.database().ref("users/ada");
ref.once("value")
.then(function(snapshot) { var a = snapshot.hasChildren(); // true
var b = snapshot.child("name").hasChildren(); // true
var c = snapshot.child("name/first").hasChildren(); // false
});

>> numChildren

// Assume we have the following data in the Database:{ "name": { "first": "Ada", "last": "Lovelace"
}
}var ref = admin.database().ref("users/ada");
ref.once("value")
.then(function(snapshot) { var a = snapshot.numChildren(); // 1 ("name")
var b = snapshot.child("name").numChildren(); // 2 ("first", "last")
var c = snapshot.child("name/first").numChildren(); // 0
});

admin.database.Query

>> orderByChild

var ref = admin.database().ref("dinosaurs");
ref.orderByChild("height").on("child_added", function(snapshot) {
console.log(snapshot.key + " was " + snapshot.val().height + " m tall");
});

>> orderByKey

var ref = admin.database().ref("dinosaurs");
ref.orderByKey().on("child_added", function(snapshot) {
console.log(snapshot.key);
});

>> orderByValue

var scoresRef = admin.database().ref("scores");
scoresRef.orderByValue().limitToLast(3).on("value", function(snapshot) {
snapshot.forEach(function(data) {
console.log("The " + data.key + " score is " + data.val());
});
});

>> startAt, endAt

// Find all dinosaurs that are at least three meters tall.var ref = admin.database().ref("dinosaurs");
ref.orderByChild("height").startAt(3).on("child_added", function(snapshot) {
console.log(snapshot.key)
});// Find all dinosaurs whose names come before Pterodactyl lexicographically.var ref = admin.database().ref("dinosaurs");
ref.orderByKey().endAt("pterodactyl").on("child_added", function(snapshot) {
console.log(snapshot.key);
});

>> limitToFirst, limitToLast

// Find the two shortest dinosaurs.var ref = admin.database().ref("dinosaurs");
ref.orderByChild("height").limitToFirst(2).on("child_added", function(snapshot) { // This will be called exactly two times (unless there are less than two
// dinosaurs in the Database).

// It will also get fired again if one of the first two dinosaurs is
// removed from the data set, as a new dinosaur will now be the second
// shortest. console.log(snapshot.key);
});// Find the two heaviest dinosaurs.var ref = admin.database().ref("dinosaurs");
ref.orderByChild("weight").limitToLast(2).on("child_added", function(snapshot) { // This callback will be triggered exactly two times, unless there are
// fewer than two dinosaurs stored in the Database. It will also get fired
// for every new, heavier dinosaur that gets added to the data set. console.log(snapshot.key);
});

>> equalTo

// Find all dinosaurs whose height is exactly 25 meters.var ref = admin.database().ref("dinosaurs");
ref.orderByChild("height").equalTo(25).on("child_added", function(snapshot) {
console.log(snapshot.key);
});

>> isEqual

var rootRef = admin.database().ref();var usersRef = rootRef.child("users");

usersRef.isEqual(rootRef); // falseusersRef.isEqual(rootRef.child("users")); // trueusersRef.parent.isEqual(rootRef); // true

var rootRef = admin.database().ref();var usersRef = rootRef.child("users");var usersQuery = usersRef.limitToLast(10);

usersQuery.isEqual(usersRef); // falseusersQuery.isEqual(usersRef.limitToLast(10)); // trueusersQuery.isEqual(rootRef.limitToLast(10)); // falseusersQuery.isEqual(usersRef.orderByKey().limitToLast(10)); // false

>> toString

// Calling toString() on a root Firebase reference returns the URL where its// data is stored within the Database:var rootRef = admin.database().ref();var rootUrl = rootRef.toString();// rootUrl === "https://sample-app.firebaseio.com/".// Calling toString() at a deeper Firebase reference returns the URL of that// deep path within the Database:var adaRef = rootRef.child('users/ada');var adaURL = adaRef.toString();// adaURL === "https://sample-app.firebaseio.com/users/ada".

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