Class: Query

Extends

• WebcomBase

Members

(static, constant) FORGET :number

Type:

• number

(static, constant) KEEP :number

Type:

• number

(static, constant) KEEP_UPDATING :number

Type:

• number

authenticator :AuthenticationService

Type:

• AuthenticationService

Overrides:

• WebcomBase#authenticator

datasync :DatasyncService

Type:

• DatasyncService

Overrides:

• WebcomBase#datasync

Methods

child(pathString) → {Webcom}

Parameters:

Returns:

Type

Webcom

Example

// Get a reference to the "friends" data node
var ref = new Webcom("contacts").child("friends");

var johnRef = ref.child("john");
console.log(johnRef.name());
// ==> "/https/io.datasync.orange.com/contacts//friends/john"

var maryRef = ref.child("/mary");
console.log(maryRef.toString());
// ==> "/https/io.datasync.orange.com/contacts//friends/mary"

var maryRef2 = johnRef.child("../mary");
console.log(maryRef2.toString());
// ==> "/https/io.datasync.orange.com/contacts//friends/mary"

var nameThenLastRef = johnRef.child("name").child("last");
console.log(nameThenLastRef.toString());
// ==> "/https/io.datasync.orange.com/contacts//friends/john/name/last"

var lastNameRef = johnRef.child("name/last");
console.log(lastNameRef.toString());
// ==> "/https/io.datasync.orange.com/contacts//friends/john/name/last"

var rootRef = ref.child("../..");
console.log(rootRef.toString());
// ==> "/https/io.datasync.orange.com/contacts/"

var hashedRef = ref.child("#john");
console.log(hashedRef.toString());
// ==> "/https/io.datasync.orange.com/contacts//friends/.list.pR/3a/fH/john"

endAt(nameopt) → {Query}

Parameters:

Since:

• 2.2

Returns:

Type

Query

Example

// Get a reference to friends
var ref = new Webcom("/base/contacts/friends");

// Display friends whose names (keys) come before john
ref.endAt("john").on("value", function(snapshot){
     console.log(snapshot.val());
});

equalTo(nameopt) → {Query}

Parameters:

Since:

• 2.2

Returns:

Type

Query

Example

// Get a reference to friends
var ref = new Webcom("/base/contacts/friends");

// Display friends whose names (keys) is exactly john
ref.equalTo("john").on("value", function(snapshot){
     console.log(snapshot.val());
});

get() → {Promise.<DataSnapshot>}

Since:

• 2.14

Returns:

Type

Promise.<DataSnapshot>

Example

// Get a reference on the "friends" node of the "contacts" application
const friendsNode = new Webcom("contacts").child("friends");
// Read the value of this node
friendsNode.get()
    .then(data => {
        console.log("The 'friends' data are:", JSON.stringify(data.val()));
        console.log("They are", data.acknowledged() ? "acknowledged" : "not yet acknowledged", "by the back end");
    })
    .catch(error => console.log("Could not read data:", error.message);

getCache() → {DataSnapshot}

Since:

• 2.15

Returns:

Type

DataSnapshot

limit(lim) → {Query}

Parameters:

Since:

• 2.2

Returns:

Type

Query

Examples

Last

// Get a reference to friends
var ref = new Webcom("/base/contacts/friends");

var lastFriends = ref.endAt().limit(5);
// Display the 5 last friends
lastFriends.on("value", function(snapshot){
     console.log(snapshot.val());
});

First

// Get a reference to friends
var ref = new Webcom("/base/contacts/friends");

var lastFriends = ref.startAt().limit(5);
// Display the 5 first friends
lastFriends.on("value", function(snapshot){
     console.log(snapshot.val());
});

First starting at some key

// Get a reference to friends
var ref = new Webcom("/base/contacts/friends");

var lastFriends = ref.startAt("john").limit(5);
// Display friends whose names (keys) come after john display the following 5
lastFriends.on("value", function(snapshot){
     console.log(snapshot.val());
});

name() → (nullable) {string}

Returns:

Type

string

Example

// Get a reference to the "john" data node
var ref = new Webcom("contacts").child("friends/john");

console.log(ref.name());
// ==> "john"

console.log(ref.child("name").name());
// ==> "name"

console.log(ref.root().name());
// ==> null

off(eventTypesopt, callbackopt, contextopt)

Parameters:

Examples

Unregister a single callback

// Get a reference to the "friends" node of the "contacts" application
var ref = new Webcom("contacts").child("friends");

var onChange = ref.on("value", function(snapshot) {
  // your handler
});

// later...
ref.off("value", onChange);

Unregister several callbacks

// Get a reference to the "friends" node of the "contacts" application
var ref = new Webcom("contacts").child("friends");

var onChanged = function(snapshot) {
  // your first handler
});
var onAdded = function(snapshot) {
  // your second handler
});

ref.on("value", onChanged);
ref.on("child_added", onAdded);

// later...

// Unregister all callback functions from ref...
ref.off();
// ...or all callback function associated to a specific kind of event
ref.off("value"); // onChanged is unregistered while onAdded remains registered

offPreservingOfflineData(eventTypeopt, callbackopt, contextopt)

Parameters:

Since:

• 2.11

Deprecated:

• make the completion callbacks passed to the Query#on function return Query.KEEP_UPDATING.

on(eventTypes, callback, completionCallbackopt, contextopt) → {Query~watchCallback}

Parameters:

Returns:

Type

Query~watchCallback

Examples

Value

// Get a reference to the "friends" node of the "contacts" application
var ref = new Webcom("contacts").child("friends");

// This callback is called only when some data change under the "friends" node
ref.on("value", function(snapshot) {
  console.log("New friends value is: " + JSON.stringify(snapshot.val()));
});

Child Added

// Get a reference to the "friends" node of the "contacts" application
var ref = new Webcom("contacts").child("friends");

// This callback is called only when a new child is added to the "friends" node
ref.on("child_added", function(snapshot, prevChildName) {
  console.log("New child for friends: " + snapshot.name() + " -> " + JSON.stringify(snapshot.val()));
  if (prevChildName) {
    console.log("This new child comes after " + prevChildName);
  } else {
    console.log("This new child is the only one");
  }
});

Child Changed

// Get a reference to the "friends" node of the "contacts" application
var ref = new Webcom("contacts").child("friends");

// This callback is called only when the value of an existing child of the "friends" node changes
ref.on("child_changed", function(snapshot, prevChildName) {
  console.log("The " + snapshot.name() + " child has changed value to: " + JSON.stringify(snapshot.val()));
  if (prevChildName) {
    console.log("This child comes after " + prevChildName);
  } else {
    console.log("This child is the only one");
  }
});

Child Removed

// Get a reference to the "friends" node of the "contacts" application
var ref = new Webcom("contacts").child("friends");

// This callback is called only when a child of the "friends" node is removed
ref.on("child_removed", function(snapshot) {
  console.log("The " + snapshot.name() + " child has been removed, its value was: " +
    JSON.stringify(snapshot.val()));
});

once(eventType, callback, cancelCallbackopt, contextopt)

Parameters:

Deprecated:

• use Query#get instead.

Examples

// Get a reference to the "friends" node of the "contacts" application
var ref = new Webcom("contacts").child("friends");

// Read the value of the "friends" node
ref.once("value", function(snapshot) {
  console.log("The value of the " + snapshot.name() + " node is: " + JSON.stringify(snapshot.val()));
});

// Get a reference to the "friends" node of the "contacts" application
var ref = new Webcom("contacts").child("friends");

// Check the read permission on the "friends" node
ref.once("value", function() {}, function(error) {
  console.log("Insufficient read permission");
});

parent() → {Webcom}

Returns:

Type

Webcom

Example

// Get a reference to the "friends" data node
var ref = new Webcom("contacts").child("friends");

var contactsRef = ref.parent();
console.log(contactsRef.toString());
// ==> "/https/io.datasync.orange.com/contacts/"

pathString() → {String}

Since:

• 2.6.2

Returns:

Type

String

ref() → {Webcom}

Returns:

Type

Webcom

Example

// Get a reference to the "friends" data node
var ref = new Webcom("contacts").child("friends");

var query = ref.limit(2);
var refSameLocation = query.ref(); //ref === refSameLocation

root() → {Webcom}

Returns:

Type

Webcom

Example

// Get a reference to the "john" data node
var ref = new Webcom("contacts").child("friends/john");

var rootRef = ref.root();
console.log(rootRef.toString());
// ==> "/https/io.datasync.orange.com/contacts/"

startAt(nameopt, nullable) → {Query}

Parameters:

Since:

• 2.2

Returns:

Type

Query

Example

// Get a reference to friends
var ref = new Webcom("/base/contacts/friends");

// Display friends whose names (keys) come after john
ref.startAt("john").on("value", function(snapshot){
     console.log(snapshot.val());
});

Type Definitions

completionCallback(errornullable) → {number}

Parameters:

See:

• Query#on and Query#off

Returns:

Type

number

watchCallback(snapshot, prevChildNameopt, nullable)

Parameters:

See:

• Query#on, Query#once and Query#off