Nrthugu

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));