无法读取未定义的属性“transaction”。React Native

Question

我是第一次接触React-Native，我在GitHub上遵循了react-native-sqlite-storage上的步骤，但不幸的是，我被事务卡住了，我已经尝试过enablePromises，但它仍然不起作用。我有点不知所措，不知道该怎么做。

import React from 'react';
import SQLite from 'react-native-sqlite-storage';
import { StyleSheet, Text, View, ListItem } from 'react-native';
  
  export default function App() {
  
      let db = SQLite.openDatabase(
        {
          name: 'users',
          createFromLocation: 1,
        },
        successToOpenDB(),
        failToOpenDB()
      );
  
      function successToOpenDB() {
        db.transaction((tx) => {
          tx.executeSql('SELECT * FROM USERS', [], (tx, results) => {
            let dataLength = results.row.length;
            alert(dataLength);
          });
        });
      }
  
    function failToOpenDB(err) {
      console.log(err);
    }
  
    return (
      <>
        <View style={styles.header}>
          <Text style={styles.headerText}>Title</Text>
  
        </View>

      </>
    );
  };

谢谢!

Answer 1

您正在传递成功的回调successToOpenDB函数，同时连接到数据库并使用未定义的" db“，并且您收到错误"cannot read property transaction of undefined.So do not pass successToOpenDB function as a success callback”。

errorCB(err) {
  console.log("SQL Error: " + err);
},

successCB() {
  console.log("SQL executed fine");
},

openCB() {
  console.log("Database OPENED");
},

var db = SQLite.openDatabase({
          name: 'users',
          createFromLocation: 1,
        }, openCB, errorCB);
db.transaction((tx) => {
  tx.executeSql('SELECT * FROM Employees a, Departments b WHERE a.department = b.department_id', [], (tx, results) => {
      console.log("Query completed");

      // Get rows with Web SQL Database spec compliance.

      var len = results.rows.length;
      for (let i = 0; i < len; i++) {
        let row = results.rows.item(i);
        console.log(`Employee name: ${row.name}, Dept Name: ${row.deptName}`);
      }

      // Alternatively, you can use the non-standard raw method.

      /*
        let rows = results.rows.raw(); // shallow copy of rows Array

        rows.map(row => console.log(`Employee name: ${row.name}, Dept Name: ${row.deptName}`));
      */
    });
});