Array From Observable Returning Undefined

Question

I tried subscribing to an observable returning an array, the array object print to console quite well, but accessing the content of the array raise undefined error and array.length print out 0;

The observable generating fetching the return array from datastore

getDataFromDatabase(sqlStatement: string, querydata?: any[]): Observable<any> {
    let datas: Array<any> = [];
    this.database.executeSql(sqlStatement, querydata ? querydata : []).then((data) => {
        let len = data.rows.length;
        console.log('database data.rows', data.rows);
        for (let i = 0; i < len; i++) {
            let d = data.rows.item(i);
            datas.push(d);
        }
    },
        (err) => {
            datas = err;
        }
    );

    return observable.forkJoin(observable.of(datas));
}

The function subscribing to the observable

checkIfFirstTime(): Observable<number> {
    this.database.getDatabaseState().subscribe(state => {
        if (state) {
            let query = "SELECT appLaunch AS al FROM User WHERE id = ?";
            this.database.getDataFromDatabase(query, [1]).subscribe(data => {
                if (data != null) {
                    data = data[0];
                    console.log(data.length, ' - Check-auth.service 1...', data);
                    if (data[0].al) {
                        let query2 = "SELECT pin AS pin FROM Setting WHERE id = ?";
                        console.log(query2);
                        this.database.getDataFromDatabase(query2, [200]).subscribe(data2 => {
                            data2 = data2[0];
                            if (data2[0].pin && this.login) {
                                this.authIndex = 1;
                            }
                            else if (data2[0].pin && (!this.login)) {
                                this.authIndex = 3;
                            }
                            else if (!data2[0].pin) {
                                this.authIndex = 1;
                            }
                        });
                    }
                    else if (!data[0].al) {
                        console.log('hey am here');
                        this.authIndex = 2;
                    }
                }
            });
        }
    });

    return observer.of(this.authIndex);
}

Error result

Array(1)0: {al: 0}length: 1__proto__: Array(0) "Check-auth.service 1..." Array(1)0: [{…}]length: 1__proto__: Array(0) "....3" 1 vendor.js:55437 ERROR TypeError: Cannot read property 'al' of undefined at SafeSubscriber._next (default~home-home-module~pages-calendar-calendar-module~pages-pin-link-pin-link-module~pages-reminde~b3c38b73.js:9057) at SafeSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.SafeSubscriber.__tryOrUnsub (vendor.js:94208) at SafeSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.SafeSubscriber.next (vendor.js:94146) at Subscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber._next (vendor.js:94089) at Subscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.next (vendor.js:94066) at ForkJoinSubscriber.push../node_modules/rxjs/_esm5/internal/observable/forkJoin.js.ForkJoinSubscriber.notifyComplete (vendor.js:95234) at InnerSubscriber.push../node_modules/rxjs/_esm5/internal/InnerSubscriber.js.InnerSubscriber._complete (vendor.js:93292) at InnerSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.complete (vendor.js:94078) at vendor.js:104694 at subscribeToResult (vendor.js:104875) defaultErrorLogger @ vendor.js:55437 main.js:3124 database data.rows Object`

checkIfFirstTime is a very serious case of arrow head code, you should work on avoid writing code like that. Flattening such arrows makes the code much more maintainable. — hlovdal
– hlovdal, Commented Oct 25, 2022 at 14:55

maryrio7 · Accepted Answer · 2019-09-26 08:12:03Z

1

 this.database.getDataFromDatabase(query, [1]).subscribe(data=>{
                if(data!=null){
                    data = data[0];

You are overriding the data that you get and is no longer an array, so it can't get 'al' at pos[0].

Try to use different and more descriptive names to your variables to not get confused.

answered Sep 26, 2019 at 8:12

maryrio7

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1 Comment

T. Xplicit Over a year ago

the forkjoin() function create another array making the array a 2x2 array the original data is data[0][0].al so i decide to to pass data to data[0] to data;

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