database

My “Scala Flat File Database” project now handles newline characters alvin January 15, 2018 - 9:26pm

I updated my Scala Flat File Database project so it now handles newline (\n) characters. The solution isn’t perfect, but it’s a start, and makes the approach much more usable. (I didn’t need this functionality until today, so I didn’t know it was a problem.) I also updated it to work with Scala 2.12.

Android Room, database I/O, and Java 8 threads

I just started working with the Android Room database persistence library, and since you’re not supposed to run things like database queries on the main thread (the UI thread), I was looking at other ways to run them.

In general, you probably won’t want to run database queries using a Thread, but just to see how Room works, I wrote this Java Thread code, and confirmed that it works as expected:

An example of Android StrictMode output (with improper database access)

I was just working with an example of how to use Android’s new Room Persistence Library, and the example I was working with ran some of its code on the main Android thread, also known as its “UI thread.” I knew this was bad, but I wanted to start with someone’s example, and then figure out a good way to get the Room method calls to run on a background thread, such as using an AsyncTask. (The Android docs don’t specify a “best practice” for this atm.)

How to search for a string in all fields of every table in a MySQL database

Here’s a cool tip: if you want to search for a text string in all fields of all tables of a MySQL database, you can use phpMyAdmin to do this very easily. Here are the steps to search every MySQL database table.

1) Select the desired database

The first step is to select the database you want to search. Don’t select a table — just select the database you want to search. (If you select a table you’ll get a different search form in Step 2.)

A simple way to populate an Android ListView with a SQLite database Cursor alvin January 25, 2017 - 7:53pm

Here’s an example of how to populate an Android ListView, where I get the data for the ListView from a database Cursor:

DatabaseHelper.TeamsCursor tc = DatabaseManager.get(getActivity()).getAllTeams();
ArrayList<String> listOfTeamNames = new ArrayList<>();
for(tc.moveToFirst(); !tc.isAfterLast(); tc.moveToNext()) {
    listOfTeamNames.add(tc.getTeam().teamName);
}

// list the team names with an adapter that talks to our listview
TeamNamesAdapter adapter = new TeamNamesAdapter(listOfTeamNames);
setListAdapter(adapter);

There are more formal ways to create an adapter class to work with a Cursor, but for my needs I just needed to get a list of names from a SQLite database table and show them in a simple ListView — part of a ListFragment — and this was the simplest code to write.

FWIW, the example also shows one way to iterate over the elements in a Cursor using a Java for loop.

Android SQLiteOpenHelper example source code

Here’s an Android SQLite class I use in an Android app I wrote in 2014-2015. I’m sharing it here so I can easily find an Android SQLiteOpenHelper example: