Retrieving JSON Data¶
JSON values are stored in database columns of type JSON
. The data retrieval mechanism for JSON values is the same as for any other data stored in Backendless database. You can use the data retrieval API to retrieve objects from the Backendless database. Data in the JSON
columns is returned to the client application as either a strongly-typed object or as . Consider the example below:
Suppose the database stores objects in the Person
data table. The table declares the profile
column of type JSON. The column contains JSON values in the following format:
{ "age": 55, "name": "Bob", "address": { "city": "Los Angeles", "state": "California", "street": "123 Santa Monica Blvd." }, "lastname": "Smith", "favoriteColors": [ "Blue", "Red" ], "favoriteNumbers": [ 13, 21, 88 ] }
As you can see the sample JSON value above exhibits the following "qualities":
- literal string and numeric values -
age
,name
andlastname
keys. - an array consisting of strings -
favoriteColors
- an array consisting of numbers -
favoriteNumbers
- an enclosed JSON object in the
address
key.
The JSON values and the Person objects may appear as shown below in the database:
Suppose the client application needs to retrieve both Person
objects and the corresponding profile
values . This can be accomplished with the following code:
const person = await Backendless.Data.of('Person').findById('AE2B0CBD-A5A9-453C-9F9A-E15481DF3C02') const { profile } = person console.log('Name:', profile.name) console.log('Last name:', profile.lastname) console.log('Age:', profile.age) console.log('Favorite numbers:', profile.favoriteNumbers) console.log('Favorite colors:', profile.favoriteColors) const { address } = profile console.log('Street:', address.street) console.log('City:', address.city) console.log('State:', address.state)
The code produces the following log output:
Name Bob Last name Smith Age 55 Favorite numbers [13, 21, 88] Favorite colors [Blue, Red] Street 123 Santa Monica Blvd. City Los Angeles State California
As you can see, the entire JSON structure is converted to a JavaScript object with all the key/value pairs becoming corresponding entries in the returned object.
Your application may use an alternative approach - representing objects in the Backendless database with strongly-typed classes. In the context of the example above, this means you will have the Person
class defined in your application. See the example below:
Address class:
// declare custom Address class class Address { constructor(address) { address = address || {} this.street = address.street this.city = address.city this.state = address.state } setStreet(street) { this.street = street return this } getStreet() { return this.street } setCity(city) { this.city = city return this } getCity() { return this.city } setState(state) { this.state = state return this } getState() { return this.state } }
class Profile { constructor(profile) { profile = profile || {} this.name = profile.name this.age = profile.age this.favoriteNumbers = profile.favoriteNumbers this.favoriteColors = profile.favoriteColors this.address = new Address(profile.address) } setName(name) { this.name = name return this } getName() { return this.name } setAge(age) { this.age = age return this } getAge() { return this.age } setFavoriteNumbers(favoriteNumbers) { this.favoriteNumbers = favoriteNumbers return this } getFavoriteNumbers() { return this.favoriteNumbers } setFavoriteColors(favoriteColors) { this.favoriteColors = favoriteColors return this } setAddress(address) { this.address = new Address(address) return this } getAddress() { return this.address } }
class Person { constructor(person) { person = person || {} this.profile = new Profile(person.profile) } setProfile(profile) { this.profile = new Profile(profile) return this } getProfile() { return this.profile } }
const personObject = await Backendless.Data.of('Person').findById('AE2B0CBD-A5A9-453C-9F9A-E15481DF3C02') const person = new Person(personObject) // initialize person as Person class
In case when the JSON values are represented as strongly-typed classes, Backendless automatically adapts them to the instances of your classes. It is important to maintain the basic fidelity between the JSON types and the corresponding types as shown below: