Ionic2/Angular2 wait for SQLite database to open before querying

Question

I'm using Ionic 2 (Angular 2) for a Hybrid app. I inject a shared provider into the page that will display data from my SQLite3 database and then proceed to load the data. However, on creation of my database provider opening the database takes some time (very little). My code (as of this moment) however does not wait for the database to be opened before querying, which obviously results in an error.

How can I structure my code that it will wait for the database to be opened in order to evade a crash?

The constructor of my database provider:

constructor(private platform: Platform) {
this.platform.ready().then(() => {
  if(this.isOpen !== true) {
    this.storage = new SQLite();

    this.storage.openDatabase({name: "data.db", location: "default"}).then(() => {
      this.isOpen = true;
      this.storage.executeSql("CREATE TABLE IF NOT EXISTS people (id INTEGER PRIMARY KEY AUTOINCREMENT, firstname TEXT, lastname TEXT)", []);
    });
  }
});
console.log('Hello Database Provider');

This provider gets injected into the constructor of my page.

When the page (home page) is loaded it triggers an event that calls a load() function.

ionViewDidLoad() {
this.load();
console.log('Hello Home Page');

The load function:

public load() {
this.database.getPeople().then((result) => {
  this.itemList = <Array<Object>> result;
}, (error) => {
  console.log("LOAD ERROR: ", error);
});

I'm very much hoping someone can point me in the right direction :)

@dermoritz I've resolved this problem and added my solution as an answer :) — enemypixel
– enemypixel, Commented Mar 8, 2017 at 18:17

enemypixel · Accepted Answer · 2017-03-08 18:16:41Z

I've finally found a solution to my problem.

For starters I've added a function to my provider that checks if the database is loaded, if it isn't it proceeds to load it:

public openSQLiteDatabase() {
return new Promise((resolve, reject) => {
  if(this.isOpen) {
    console.log("DB IS OPEN");
    resolve(this.isOpen);
  }

  else {
    console.log("DB IS NOT OPEN");
    this.platform.ready().then(() => {
      this.storage.openDatabase({name: "data.db", location: "default"}).then(() => {
        this.appsettings.openSQLiteDatabase().then(() => {
          this.appsettings.getSettings().then((result) => {
            let settings: Settings = <Settings> result;
            this.selectedDataset = settings.selectedDataset;
            this.isOpen = true;
            resolve(this.isOpen);
          });
        });
      }, (error) => {
        reject(error);
      });
    });
  }
});}

As this function returns a promise (JS Promises) it allows me to wait for the database to be opened before doing anything else (such as querying).

My function in the page-specific TypeScript file:

ionViewDidLoad() {
this.database.openSQLiteDatabase().then(() => {
  this.loadDictionary();
});}

With code like this I never have problems with queries being performed before my database has been opened!

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