使用 SQLite 作为 key:value 存储

Question

正如的评论和其他问题中所建议的，SQLite 完全可以用作持久性 key:value 存储。

您将如何定义一个 class（或只是包装函数），以便将 key:value 存储与 SQLite 一起使用就像这样简单：

kv = Keyvaluestore('/test.db')
kv['hello'] = 'hi'        # set
print(kv['hello'])         # get
print('blah' in kv)        # answer: False because there's no key 'blah' in the store
kv.close()

?

Answer 1

已经有 sqlitedict 似乎可以满足您的所有需求。

来自文档：

from sqlitedict import SqliteDict
mydict = SqliteDict('./my_db.sqlite', autocommit=True)
mydict['some_key'] = any_picklable_object
print(mydict['some_key'])  # prints the new value
for key, value in mydict.iteritems():
    print(key, value)
print(len(mydict))  # etc... all dict functions work
mydict.close()

Answer 2

即使存在执行此操作的模块（请参阅其他答案），我也尝试编写一个简单、独立的版本。这是一个 class KeyValueStore（键和值是字符串），其工作方式如下：

演示

from sqlitekeyvaluestore import KeyValueStore

kv = KeyValueStore('test.db')  # uses SQLite

print(len(kv))                 # 0 item
kv['hello1'] = 'you1'
kv['hello2'] = 'you2'
kv['hello3'] = 'you3'
print(kv['hello1'])            # you1
print(len(kv))                 # 3 items

del kv['hello1']
print(len(kv))                 # 2 items remaining

print('hello1' in kv)          # False, it has just been deleted!
print('hello3' in kv)          # True

kv['hello3'] = 'newvalue'      # redefine an already present key/value
print(kv['hello3'])            # newvalue

print(kv.keys())               # ['hello2', 'hello3']
print(kv.values())             # ['you2', 'newvalue']
print(kv.items())              # [('hello2', 'you2'), ('hello3', 'newvalue')]

for k in kv:
    print(k, kv[k])

kv.close()                     # important to commit

代码：sqlitekeyvaluestore.py

import sqlite3

class KeyValueStore(dict):
    def __init__(self, filename=None):
        self.conn = sqlite3.connect(filename)
        self.conn.execute("CREATE TABLE IF NOT EXISTS kv (key text unique, value text)")

    def close(self):
        self.conn.commit()
        self.conn.close()

    def __len__(self):
        rows = self.conn.execute('SELECT COUNT(*) FROM kv').fetchone()[0]
        return rows if rows is not None else 0

    def iterkeys(self):
        c = self.conn.cursor()
        for row in c.execute('SELECT key FROM kv'):
            yield row[0]

    def itervalues(self):
        c = self.conn.cursor()
        for row in c.execute('SELECT value FROM kv'):
            yield row[0]

    def iteritems(self):
        c = self.conn.cursor()
        for row in c.execute('SELECT key, value FROM kv'):
            yield row[0], row[1]

    def keys(self):
        return list(self.iterkeys())

    def values(self):
        return list(self.itervalues())

    def items(self):
        return list(self.iteritems())

    def __contains__(self, key):
        return self.conn.execute('SELECT 1 FROM kv WHERE key = ?', (key,)).fetchone() is not None

    def __getitem__(self, key):
        item = self.conn.execute('SELECT value FROM kv WHERE key = ?', (key,)).fetchone()
        if item is None:
            raise KeyError(key)
        return item[0]

    def __setitem__(self, key, value):
        self.conn.execute('REPLACE INTO kv (key, value) VALUES (?,?)', (key, value))

    def __delitem__(self, key):
        if key not in self:
            raise KeyError(key)
        self.conn.execute('DELETE FROM kv WHERE key = ?', (key,))

    def __iter__(self):
        return self.iterkeys()

Answer 3

我喜欢 Basj 的回答，但我还想在 KeyValueStore class 中添加以下函数，以便在使用数据库时，我们可以提交数据而不必关闭数据库。

class KeyValueStore(dict):
    """Other functions"""
    def commit(self):
        self.conn.commit()

Answer 4

sqlite3dbm 提供此功能，同时保留传统的 dbm 界面。它是一个比 sqlitedict 更简单的界面，当你只需要一个非常基本的 key-value 商店时。它还包括一个方便的 class，可以使用 python 的 shelve 功能将任意对象存储为值。

使用 SQLite 作为 key:value 存储

Use SQLite as a key:value store

python

sqlite

dictionary

key-value

key-value-store

演示

代码：sqlitekeyvaluestore.py