Return data to component from DB helper class react native










0
















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.










share|improve this question


























    0
















    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.










    share|improve this question
























      0












      0








      0









      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.










      share|improve this question















      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.







      sqlite react-native






      share|improve this question













      share|improve this question











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      share|improve this question










      asked Nov 12 '18 at 7:57









      Sandip NagSandip Nag

      125210




      125210






















          1 Answer
          1






          active

          oldest

          votes


















          1














          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));






          share|improve this answer






















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            1 Answer
            1






            active

            oldest

            votes








            1 Answer
            1






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            1














            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));






            share|improve this answer



























              1














              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));






              share|improve this answer

























                1












                1








                1







                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));






                share|improve this answer













                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));







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered Nov 12 '18 at 8:39









                parohyparohy

                881920




                881920



























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