SCAN：以渐进方式迭代数据库中的键

redis> SCAN 0
1) "25" -- 进行下次迭代的游标
2) 1) "key::16" -- 本次迭代获取到的键
2) "key::2"
3) "key::6"
4) "key::8"
5) "key::13"
6) "key::22"
7) "key::10"
8) "key::24"
9) "key::23"
10) "key::21"
11) "key::5"

redis> SCAN 25
1) "31"
2) 1) "key::20"
2) "key::18"
3) "key::19"
4) "key::7"
5) "key::1"
6) "key::9"
7) "key::12"
8) "key::11"
9) "key::17"
10) "key::15"
11) "key::14"
12) "key::3"

redis> SCAN 31
1) "0"
2) 1) "key::0"
2) "key::4"

SCAN cursor [MATCH pattern]

redis> SCAN 0 MATCH user::*
1) "208"
2) 1) "user::1"
2) "user::65"
3) "user::99"
4) "user::51"
redis> SCAN 208 MATCH user::*
1) "232"
2) 1) "user::13"
2) "user::28"
3) "user::83"
4) "user::14"
5) "user::61"
-- 省略后续的其他迭代……

SCAN cursor[COUNT number]

redis> SCAN 0 COUNT 5
1) "160"
2) 1) "key::43"
2) "key::s"
3) "user::1"
4) "key::83"
5) "key::u"
redis> SCAN 0 MATCH user::* COUNT 10
1) "208"
2) 1) "user::1"
2) "user::65"
3) "user::99"
4) "user::51"
redis> SCAN 0 MATCH key::* COUNT 100
1) "214"
2) 1) "key::43"
2) "key::s"
3) "key::83"
-- 其他键……
50) "key::28"
51) "key::34"

SCAN cursor
SCAN cursor COUNT 10

HSCAN hash cursor [MATCH pattern] [COUNT number]

redis> HSCAN user::10086::profile 0
1) "0" -- 下次迭代的游标
2) 1) "name" -- 键
2) "peter" -- 值
3) "age"
4) "32"
5) "gender"
6) "male"
7) "blog"
8) "peter123.whatpress.com"
9) "email"
10) "peter123@example.com"

SSCAN set cursor [MATCH pattern] [COUNT number]

redis> SSCAN fruits 0
1) "0" -- 下次迭代的游标
2) 1) "apple" -- 集合元素
2) "watermelon"
3) "mango"
4) "cherry"
5) "banana"
6) "dragon fruit"

ZSCAN sorted_set cursor [MATCH pattern] [COUNT number]

redis> ZSCAN fruits-price 0
1) "0" -- 下次迭代的游标
2) 1) "watermelon" -- 成员
2) "3.5" -- 分值
3) "banana"
4) "4.5"
5) "mango"
6) "5"
7) "dragon fruit"
8) "6"
9) "cherry"
10) "7"
11) "apple"
12) "8.5"

class DbIterator:

    def __init__(self, client, match=None, count=None):
        """
        创建一个新的迭代器。
        可选的 match 参数用于指定迭代的匹配模式，
        而可选的 count 参数则用于指定我们期待每次迭代能够返回的键数量。
        """
        self.client = client
        self.match = match
        self.count = count
        # 当前迭代游标
        self.current_cursor = 0
        # 记录迭代是否已经完成的状态变量
        self.iteration_is_over = False

    def next(self):
        """
        以列表形式返回当前被迭代到的数据库键，
        返回 None 则表示本次迭代已经完成。
        """
        if self.iteration_is_over:
            return None
        # 获取下次迭代的游标以及当前被迭代的数据库键
        next_cursor, keys = self.client.scan(self.current_cursor, self.match, self.count)
        # 如果下次迭代的游标为 0 ，那么表示迭代已完成
        if next_cursor == 0:
            self.iteration_is_over = True
        # 更新游标
        self.current_cursor = next_cursor
        # 返回当前被迭代的数据库键
        return keys

>>> from redis import Redis
>>> from db_iterator import DbIterator
>>> client = Redis(decode_responses=True)
>>> for i in range(50): # 向数据库插入50个键
... key = "key{0}".format(i)
... value = i
... client.set(key, value)
...
True
True
...
True
>>> iterator = DbIterator(client)
>>> iterator.next() # 开始迭代
['key46', 'key1', 'key27', 'key39', 'key15', 'key0', 'key43', 'key12', 'key49', 'key41', 'key10'
]
>>> iterator.next()
['key23', 'key7', 'key9', 'key20', 'key18', 'key3', 'key5', 'key34', 'key32', 'key40']
>>> iterator.next()
['key4', 'key33', 'key30', 'key45', 'key38', 'key31', 'key6', 'key16', 'key25', 'key14', 'key13'
]
>>> iterator.next()
['key29', 'key2', 'key42', 'key11', 'key48', 'key28', 'key8', 'key44', 'key21', 'key26']
>>> iterator.next()
['key22', 'key47', 'key36', 'key17', 'key19', 'key24', 'key35', 'key37']
>>> iterator.next() # 迭代结束
>>>

scan_iter(self, match=None, count=None) unbound redis.client.Redis method
  Make an iterator using the SCAN command so that the client doesn't
  need to remember the cursor position.
  "match" allows for filtering the keys by pattern
  "count" allows for hint the minimum number of returns

>>> from redis import Redis
>>> client = Redis(decode_responses=True)
>>> client.mset({"k1":"v1", "k2":"v2", "k3":"v3"})
True
>>> for key in client.scan_iter():
... print(key)
...
k1
k3
k2