OneQuery.java

package se.emilsjolander.sprinkles;

import java.util.Arrays;
import java.util.List;

import android.annotation.TargetApi;
import android.app.LoaderManager;
import android.app.LoaderManager.LoaderCallbacks;
import android.content.Loader;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Build;
import android.os.Bundle;

/**
 * Object representing a Query that will return a single result.
 * 
 * @param <T>
 *            The type of model to return
 */
public final class OneQuery<T extends Model> {

	/**
	 * Implement to get results delivered from a asynchronous query.
	 * 
	 * @param <T>
	 *            The type of model that the result will represent.
	 */
	public interface ResultHandler<T extends Model> {

		/**
		 * @param result
		 *            The result of the query.
		 * 
		 * @return whether or not you want updated result when something changes in the underlying data.
		 * 
		 */
		boolean handleResult(T result);
	}

	Class<T> resultClass;
	String sqlQuery;

	OneQuery() {
	}

	/**
	 * Execute the query synchronously
	 * 
	 * @return the result of the query.
	 */
	public T get() {
		final SQLiteDatabase db = Sprinkles.getDatabase();
		final Cursor c = db.rawQuery(sqlQuery, null);

		T result = null;
		if (c.moveToFirst()) {
			List<String> colNames = Arrays.asList(c.getColumnNames());
			result = Utils.getResultFromCursor(resultClass, c, colNames);
		}

		c.close();
		return result;
	}

	/**
	 * Execute the query synchronously
	 * 
	 * @return the result of the query.
	 */
	public boolean exists() {
		final SQLiteDatabase db = Sprinkles.getDatabase();
		final Cursor c = db.rawQuery(sqlQuery, null);

		boolean result = c.getCount() > 0;

		c.close();
		return result;
	}

	/**
	 * Execute the query asynchronously
	 * 
	 * @param lm
	 *            The loader manager to use for loading the data
	 * 
	 * @param handler
	 *            The ResultHandler to notify of the query result and any updates to that result.
	 * 
	 * @param respondsToUpdatedOf
	 *            A list of models excluding the queried model that should also trigger a update to the result if they change.
	 */
	@SuppressWarnings("unchecked")
	@TargetApi(Build.VERSION_CODES.HONEYCOMB)
	public void getAsync(LoaderManager lm, ResultHandler<T> handler, Class<? extends Model>... respondsToUpdatedOf) {
		if (Model.class.isAssignableFrom(resultClass)) {
			respondsToUpdatedOf = Utils.concatArrays(respondsToUpdatedOf, new Class[] { resultClass });
		}
		final int loaderId = sqlQuery.hashCode();
		lm.initLoader(loaderId, null, getLoaderCallbacks(sqlQuery, resultClass, handler, respondsToUpdatedOf));
	}

	@TargetApi(Build.VERSION_CODES.HONEYCOMB)
	private LoaderCallbacks<Cursor> getLoaderCallbacks(final String sqlQuery, final Class<T> resultClass, final ResultHandler<T> handler, final Class<? extends Model>[] respondsToUpdatedOf) {
		return new LoaderCallbacks<Cursor>() {

			@Override
			public void onLoaderReset(Loader<Cursor> loader) {
				if (!loader.isAbandoned()) {
					handler.handleResult(null);
				}
			}

			@Override
			public void onLoadFinished(Loader<Cursor> loader, Cursor c) {
				T result = null;
				if (c.moveToFirst()) {
					List<String> colNames = Arrays.asList(c.getColumnNames());
					result = Utils.getResultFromCursor(resultClass, c, colNames);
				}

				if (!handler.handleResult(result)) {
					loader.abandon();
				}
			}

			@Override
			public Loader<Cursor> onCreateLoader(int id, Bundle args) {
				return new CursorLoader(Sprinkles.sInstance.mContext, sqlQuery, respondsToUpdatedOf);
			}
		};
	}

}