DatabaseHelper.java

/*
 * Copyright (C) 2012 Jimmy Theis. Licensed under the MIT License:
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package com.jetheis.android.grades.storage;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DatabaseHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "gradecalc-data.db.sqlite";
    private static final int DATABASE_VERSION = 1;

    private static DatabaseHelper sInstance;

    private static final String COURSES_TABLE = "courses";
    private static final String COURSES_TABLE_CREATION_STATEMENT;

    static {
        StringBuilder builder = new StringBuilder();
        builder.append("CREATE TABLE ");
        builder.append(COURSES_TABLE);
        builder.append(" (_id INTEGER PRIMARY KEY AUTOINCREMENT");
        builder.append(", name TEXT NOT NULL");
        builder.append(", grade_type INTEGER NOT NULL");
        builder.append(")");
        COURSES_TABLE_CREATION_STATEMENT = builder.toString();
    }

    private static final String GRADE_COMPONENTS_TABLE = "grade_components";
    private static final String GRADE_COMPONENTS_TABLE_CREATION_STATEMENT;

    static {
        StringBuilder builder = new StringBuilder();
        builder.append("CREATE TABLE ");
        builder.append(GRADE_COMPONENTS_TABLE);
        builder.append(" (_id INTEGER PRIMARY KEY AUTOINCREMENT");
        builder.append(", _course_id INTEGER NOT NULL");
        builder.append(", name TEXT NOT NULL");
        builder.append(", earned REAL NOT NULL");
        builder.append(", total REAL NOT NULL");
        builder.append(")");
        GRADE_COMPONENTS_TABLE_CREATION_STATEMENT = builder.toString();
    }

    private SQLiteDatabase mDb;

    /**
     * Default constructor. Takes a {@link Context} only, because the database
     * name and version are populated from private static variables.
     * 
     * @param context
     *            The {@link Context} to initialize this {@link DatabaseHelper}
     *            with.
     */
    private DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        mDb = getWritableDatabase();
    }

    public static void initializeDatabaseHelper(Context context) {
        if (sInstance != null && sInstance.getDb() != null) {
            // Close the database connection in a DatabaseHelper instance
            // already existed.
            sInstance.getDb().close();
        }

        sInstance = new DatabaseHelper(context);
    }

    public static DatabaseHelper getInstance() {
        if (sInstance == null) {
            throw new IllegalStateException("DatabaseHelper has not been initialized yet");
        }

        return sInstance;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(COURSES_TABLE_CREATION_STATEMENT);
        db.execSQL(GRADE_COMPONENTS_TABLE_CREATION_STATEMENT);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE " + COURSES_TABLE);
        db.execSQL("DROP TABLE " + GRADE_COMPONENTS_TABLE);

        onCreate(db);
    }

    /**
     * Get this instance's {@link SQLiteDatabase} instance. Because there should
     * only be one instance of {@link DatabaseHelper}, this database should be
     * the only one in existance in the app.
     * 
     * @return The {@link SQLiteDatabase}.
     */
    public SQLiteDatabase getDb() {
        return mDb;
    }

    /**
     * Close the connection to the database. This method should only be called
     * once, as the application completely exits.
     */
    public void close() {
        mDb.close();
        mDb = null;
    }
}