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I am using sqlite and I have created a db helper class. I am not getting the data from that class inside component, but if I am consoling inside db helper it is working right, but not in component. I am giving my code:-

Cartdb.js . (Helper class)

var SQLite = require('react-native-sqlite-storage')
db = SQLite.openDatabase('predefine.db', "1.0", "Predefine", -1);
class CartDB 
 constructor()

 
 totalItems = 0;
 checkCountOfProduct()
 query = "SELECT SUM(count) AS product_count FROM Predefinedcart";
 db.transaction((tx) => 
 tx.executeSql(query, , (tx, results) => 
 console.log(results.rows.item(0).product_count)
 this.totalItems = results.rows.item(0).product_count;
 return this.totalItems;
 , function (tx, error) 
 console.log('SELECT error: ' + error.message);
 );
 )
 


export default new CartDB();

Code in Component:

import CartDB from '../../../library/CartDB';
class PredefinedLayout extends React.Component
 constructor(props)
 super(props);
 console.log(CartDB.checkCountOfProduct());
 

How can I get data here? Thanks in advance.

Its an async operation, which means it is a promise. Best way would be to pass a callback to the function or return the db operation as promise and chain then. Some documentation on Promises in javascript is here.

With callback:

class CartDB 
constructor()


totalItems = 0;
checkCountOfProduct(callback)
 query = "SELECT SUM(count) AS product_count FROM Predefinedcart";
 db.transaction((tx) => 
 tx.executeSql(query, , (tx, results) => 
 console.log(results.rows.item(0).product_count)
 this.totalItems = results.rows.item(0).product_count;
 callback(this.totalItems)
 , function (tx, error) 
 console.log('SELECT error: ' + error.message);
 );
 )

and in Comp you call:
CartDB.checkCountOfProduct(count => console.log(count));

With promise:

class CartDB 
constructor()


totalItems = 0;
checkCountOfProduct()
 query = "SELECT SUM(count) AS product_count FROM Predefinedcart";
 return new Promise((resolve, reject) => db.transaction((tx) => 
 tx.executeSql(query, , (tx, results) => 
 console.log(results.rows.item(0).product_count)
 this.totalItems = results.rows.item(0).product_count;
 resolve(this.totalItems);
 , function (tx, error) 
 reject(error);
 );
 ))

and in Comp you call: CartDB.checkCountOfProduct().then(count => console.log(count));