Redis学习笔记（三）Hashes

Redis Hashes实现了字符串字段（fields）到字符串值（value）之间的映射，尤其适用于那些拥有多个字段的对象。比如，一个用户对象拥有诸如姓名、性别、年龄等字段，使用Hashes来存储它们会很方便。

Hashes对象占用内存空间较小，因此一个Hash对象能够存储很多数据：一般能够存储超过40亿个field-value对。

1.HMSET/HMGET

HMSET将指定字段设置成指定的值，可以同时设置多个field-value对；HMGET返回指定字段对应的值，可以同时获取多个field的value。

（1）命令格式

HMSET key field value [field value ...]
HMGET key field [field ...]

1 2	HMSET key field value [field value ...] HMGET key field [field ...]

（2）示例

127.0.0.1:6379> HMSET user:007 username leo birthday 2018 verified 1
OK
127.0.0.1:6379> HMGET user:007 username birthday
1) "leo"
2) "2018"

127.0.0.1:6379> HMSET user:007 username leo birthday 2018 verified 1

127.0.0.1:6379> HMGET user:007 username birthday

1) "leo"

2) "2018"

类似的，还有HSET和HGET命令，这两个命令一次只能设置或返回一个field对应的value。

2.HGETALL/HVALS/HKEYS

HGETALL返回hash对象所有field-value对；HKEYS返回所有的fields，HVALS返回所有的values。

（1）命令格式

HGETALL key
HKEYS key
HVALS key

HGETALL key

HKEYS key

HVALS key

（2）示例

127.0.0.1:6379> HMSET user:007 username leo birthday 2018 verified 1
OK
127.0.0.1:6379> HGETALL user:007
1) "username"
2) "leo"
3) "birthday"
4) "2018"
5) "verified"
6) "1"
127.0.0.1:6379> HKEYS user:007
1) "username"
2) "birthday"
3) "verified"
127.0.0.1:6379> HVALS user:007
1) "leo"
2) "2018"
3) "1"

127.0.0.1:6379> HMSET user:007 username leo birthday 2018 verified 1

127.0.0.1:6379> HGETALL user:007

1) "username"

2) "leo"

3) "birthday"

4) "2018"

5) "verified"

6) "1"

127.0.0.1:6379> HKEYS user:007

1) "username"

2) "birthday"

3) "verified"

127.0.0.1:6379> HVALS user:007

1) "leo"

2) "2018"

3) "1"

3.HINCRBY/HINCRBYFLOAT

这两个命令分别用来增加hash对象field的value值，不同点在于，value值的类型分别为整型和浮点型。

（1）命令格式

HINCRBY key field increment
HINCRBYFLOAT key field increment

1 2	HINCRBY key field increment HINCRBYFLOAT key field increment

（2）示例

127.0.0.1:6379> HSET myhash field 5
(integer) 1
127.0.0.1:6379> HINCRBY myhash field 1
(integer) 6
127.0.0.1:6379> HINCRBY myhash field -1
(integer) 5
127.0.0.1:6379> DEL myhash
(integer) 1
127.0.0.1:6379> HSET myhash field 10.50
(integer) 1
127.0.0.1:6379> HINCRBYFLOAT myhash field 0.1
"10.6"
127.0.0.1:6379> HINCRBYFLOAT myhash field -5
"5.6"

127.0.0.1:6379> HSET myhash field 5

(integer) 1

127.0.0.1:6379> HINCRBY myhash field 1

(integer) 6

127.0.0.1:6379> HINCRBY myhash field -1

(integer) 5

127.0.0.1:6379> DEL myhash

(integer) 1

127.0.0.1:6379> HSET myhash field 10.50

(integer) 1

127.0.0.1:6379> HINCRBYFLOAT myhash field 0.1

"10.6"

127.0.0.1:6379> HINCRBYFLOAT myhash field -5

"5.6"

4.HDEL/HEXISTS

HDEL用来删除一个或多个hash对象的field；HEXISTS命令用来判断hash对象的field是否存在。

（1）命令格式

HDEL key field [field ...]
HEXISTS key field

1 2	HDEL key field [field ...] HEXISTS key field

（2）示例

127.0.0.1:6379> DEL myhash
(integer) 1
127.0.0.1:6379> HSET myhash field1 "foo"
(integer) 1
127.0.0.1:6379> HEXISTS myhash field1
(integer) 1
127.0.0.1:6379> HDEL myhash field1
(integer) 1
127.0.0.1:6379> HEXISTS myhash field1
(integer) 0

127.0.0.1:6379> DEL myhash

(integer) 1

127.0.0.1:6379> HSET myhash field1 "foo"

(integer) 1

127.0.0.1:6379> HEXISTS myhash field1

(integer) 1

127.0.0.1:6379> HDEL myhash field1

(integer) 1

127.0.0.1:6379> HEXISTS myhash field1

(integer) 0

5.HLEN/HSTRLEN

HLEN命令返回hash对象中的field个数；HSTRLEN命令返回hash对象中某个field对应的value字符串的长度。

（1）命令格式

HLEN key
HSTRLEN key field

1 2	HLEN key HSTRLEN key field

（2）示例

127.0.0.1:6379> HMSET myhash field1 leo field2 male
OK
127.0.0.1:6379> HLEN myhash
(integer) 2
127.0.0.1:6379> HSTRLEN myhash field1
(integer) 3

127.0.0.1:6379> HMSET myhash field1 leo field2 male

127.0.0.1:6379> HLEN myhash

(integer) 2

127.0.0.1:6379> HSTRLEN myhash field1

(integer) 3

参考：
https://redis.io/topics/data-types-intro
https://redis.io/commands#hash

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