etl.py

import os
import glob
import psycopg2
import pandas as pd
from sql_queries import *


def process_song_file(cur, filepath):
    """Read a song file and
    insert data to songs and artists tables

    Args:
        cur (psycopg2.cursor): The psycopg2 cursor
        filepath (str): The location of the song file
    """
    # open song file
    df = pd.read_json(filepath, lines=True)
    df['year'] = df['year'].apply(lambda x: x if x != 0 else None)
    df = df.replace({pd.np.nan: None, "": None})
    
    # insert song record
    song_data = df[[
        'song_id',
        'title',
        'artist_id',
        'year',
        'duration'
    ]].values[0]
    cur.execute(song_table_insert, song_data)

    # insert artist record
    artist_data = df[[
        'artist_id',
        'artist_name',
        'artist_location',
        'artist_latitude',
        'artist_longitude'
    ]].values[0]
    cur.execute(artist_table_insert, artist_data)


def process_log_file(cur, filepath):
    """Read a log file and
    insert data to time, users and songplays tables

    Args:
        cur (psycopg2.cursor): The psycopg2 cursor
        filepath (str): The location of the log file
    """
    # open log file
    df = pd.read_json(filepath, lines=True)

    # filter by NextSong action
    df = df[df['page'] == 'NextSong']

    # convert timestamp column to datetime
    t = pd.to_datetime(df['ts'], unit='ms')

    # insert time data records
    time_data = pd.concat([
        t,
        t.dt.hour,
        t.dt.day,
        t.dt.week,
        t.dt.month,
        t.dt.year,
        t.dt.weekday], axis=1)
    column_labels = [
        'start_time',
        'hour',
        'day',
        'week',
        'month',
        'year',
        'weekday'
    ]
    time_df = pd.DataFrame(data=time_data.values, columns=column_labels)

    for i, row in time_df.iterrows():
        cur.execute(time_table_insert, list(row))

    # load user table
    user_df = df[['userId', 'firstName', 'lastName', 'gender', 'level']]

    # insert user records
    for i, row in user_df.iterrows():
        cur.execute(user_table_insert, row)

    # insert songplay records
    for index, row in df.iterrows():

        # get songid and artistid from song and artist tables
        cur.execute(song_select, (row.song, row.artist, row.length))
        results = cur.fetchone()

        if results:
            songid, artistid = results
        else:
            songid, artistid = None, None

        # insert songplay record
        songplay_data = (
            pd.to_datetime(row.ts, unit='ms'),
            row.userId,
            row.level,
            songid,
            artistid,
            row.sessionId,
            row.location,
            row.userAgent
        )
        cur.execute(songplay_table_insert, songplay_data)


def process_data(cur, conn, filepath, func):
    """Read all files from the given location and
    execute the specified function

    Args:
        cur (psycopg2.cursor): The psycopg2 cursor
        conn (psycopg2.connection): The database connection
        filepath (str): The location of files to be processed
        func (function): The function to execute
    """
    # get all files matching extension from directory
    all_files = []
    for root, dirs, files in os.walk(filepath):
        files = glob.glob(os.path.join(root, '*.json'))
        for f in files:
            all_files.append(os.path.abspath(f))

    # get total number of files found
    num_files = len(all_files)
    print('{} files found in {}'.format(num_files, filepath))

    # iterate over files and process
    for i, datafile in enumerate(all_files, 1):
        func(cur, datafile)
        conn.commit()
        print('{}/{} files processed.'.format(i, num_files))


def main():
    conn = psycopg2.connect(
        "host=127.0.0.1 dbname=sparkifydb user=student password=student"
    )
    cur = conn.cursor()

    process_data(cur, conn, filepath='data/song_data', func=process_song_file)
    process_data(cur, conn, filepath='data/log_data', func=process_log_file)

    conn.close()


if __name__ == "__main__":
    main()