Chapter16 Data Models and Relational SQL&Assignment

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最新推荐文章于 2025-06-29 19:54:05 发布

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本文链接：https://blog.youkuaiyun.com/github_33854252/article/details/51297150

本文介绍了一种使用Python从XML文件中解析音乐元数据并将其导入SQLite数据库的方法。通过创建必要的表结构，并利用XML的特性来提取数据，最终实现了音乐库的有效管理和查询。

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代码如下：

import xml.etree.ElementTree as ET
import sqlite3

conn = sqlite3.connect('trackdb.sqlite')
cur = conn.cursor()

# Make some fresh tables using executescript()
cur.executescript('''

DROP TABLE IF EXISTS Artist;
DROP TABLE IF EXISTS Album;
DROP TABLE IF EXISTS Track;
DROP TABLE IF EXISTS GENRE;

CREATE TABLE Artist (
    id  INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
    name    TEXT UNIQUE
);

CREATE TABLE Genre (
    id  INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
    name    TEXT UNIQUE
);

CREATE TABLE Album (
    id  INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
    artist_id  INTEGER,
    title   TEXT UNIQUE
);

CREATE TABLE Track (
    id  INTEGER NOT NULL PRIMARY KEY 
        AUTOINCREMENT UNIQUE,
    title TEXT  UNIQUE,
    album_id  INTEGER,
    genre_id  INTEGER,
    len INTEGER, rating INTEGER, count INTEGER
);
''')
#关于primaryID的设置：NOT NULL：不为空；AUTOINCREMENT:主键自动增加编号(必须设置主键)


fname = raw_input('Enter file name: ')
if ( len(fname) < 1 ) : fname = 'Library.xml'

# <key>Track ID</key><integer>369</integer>
# <key>Name</key><string>Another One Bites The Dust</string>
# <key>Artist</key><string>Queen</string>
# xml中的格式，lookup方法就是通过传入的参数key，返回对应text。


def lookup(d, key):
    found = False
    for child in d:
        if found : return child.text
        if child.tag == 'key' and child.text == key :
            found = True
    return None

stuff = ET.parse(fname)
all = stuff.findall('dict/dict/dict')
print 'Dict count:', len(all)
for entry in all:
    if ( lookup(entry, 'Track ID') is None ) : continue

    name = lookup(entry, 'Name')
    artist = lookup(entry, 'Artist')
    album = lookup(entry, 'Album')
    count = lookup(entry, 'Play Count')
    rating = lookup(entry, 'Rating')
    length = lookup(entry, 'Total Time')
    genre=lookup(entry,'Genre')

    if name is None or artist is None or album is None or genre is None : 
        continue

    print name, artist, album, count, rating, length,genre

    cur.execute('''INSERT OR IGNORE INTO Artist (name) 
        VALUES ( ? )''', ( artist, ) )
    cur.execute('SELECT id FROM Artist WHERE name = ? ', (artist, ))
    artist_id = cur.fetchone()[0]

    cur.execute('''INSERT OR IGNORE INTO Album (title, artist_id) 
        VALUES ( ?, ? )''', ( album, artist_id ) )
    cur.execute('SELECT id FROM Album WHERE title = ? ', (album, ))
    album_id = cur.fetchone()[0]

    cur.execute('''INSERT OR IGNORE INTO Genre(name) VALUES (?)''',(genre, ))
    #INSERT OR IGNORE：当有重复记录时忽略，返回值为0
    cur.execute('SELECT id FROM Genre WHERE name=?',(genre, ))
    genre_id=cur.fetchone()[0]

    cur.execute('''INSERT OR REPLACE INTO Track
        (title, album_id,genre_id,len, rating, count) 
        VALUES ( ?, ?, ?, ?, ? ,?)''', 
        ( name, album_id, genre_id,length, rating, count ) )

    conn.commit()

最后在SQL执行下列语句：

SELECT Track.title, Artist.name, Album.title, Genre.name 
    FROM Track JOIN Genre JOIN Album JOIN Artist 
    ON Track.genre_id = Genre.ID and Track.album_id = Album.id 
        AND Album.artist_id = Artist.id
    ORDER BY Artist.name LIMIT 3