Understanding and use of APIs--hash type commands

Hash Common Command Review

Command	Function
Hset key field value	Set hash value
Hsetnx	Set hash value, field or key must not exist
Hget	Gets the value of a file
Hdel	Delete one or more field-value
Hlen	Calculate the number of field
Hmset	Batch setup Field-value
Hmget	Get Field-value in bulk
Hexists	Determine if a field exists
Hkeys	Get all the field
Hvals	Get all the value
Hgetall	Get all the Field-value
Hincrby	Self-increment integer
Hincrbyfloat	Self-increment floating point number
Hstrlen	Calculates the length of the value string

Almost all programming languages provide a hash (hash) type, which may be called a hash, a dictionary, and an associative array.

In Redis, the hash type refers to the key value itself as a key-value pair structure , such as value={{field1,value1}, ... {Fieldn,valuen}},

The relationship between the Redis key-value pair and the hash type can be used to represent:

Note: The mapping relationship in the hash type is called field-value, note that value here refers to the field corresponding to the value, not the key corresponding to the value , be sure to pay attention to the value of the role in different contexts.

Some of the common commands for hashing are described below.

1) Set the value

Command:hset key field value

127.0. 0.1:6379> Hset User:11127.0. 0.1:6379> Hset User:11

If the setting succeeds returns 1, the reverse returns 0.

In addition, Redis provides the HSETNX command, which has the same relationship as the set and SETNX commands, except that the scope is changed from the key to field.

127.0.0.1:6379> hexists User:1name (integer)1#user:1Name exists127.0.0.1:6379> HSETNX User:1name Xiaoniao (integer)0#没有设置成功127.0.0.1:6379> Hget User:1name"Kebi"127.0.0.1:6379> HSETNX User:4name Xiaoniao (integer)1127.0.0.1:6379> Hget User:4name"Xiaoniao"#field不存在才行

2) Get the value

Command:hget key Field

127.0. 0.1:6379> Hget User:1  name"kebi"  127.0. 0.1:6379> Hget User:1  Dorm (nil)

If the key field does not exist or the key itself does not exist, nil is returned.

3) Delete Field

Command:hdel key field [field ...]

Hdel deletes one or more field fields, returning the number of field results that were successfully deleted:

127.0.0.1:6379> Hkeys User:11)"name"2)" Age"3)"Sex"127.0.0.1:6379> Hdel User:1name (integer)1127.0.0.1:6379> Hkeys User:11)" Age"2)"Sex"

Note If you want to delete the key or use del:

127.0. 0.1:6379> del User:11127.0. 0.1:6379> exists User:10

It does not say that the hash value can be deleted individually because it is meaningless.

4) Calculate the number of field

Command:hlen key

127.0.0.1:6379> Hset User:1name Kebi (integer)1127.0.0.1:6379> Hset User:1Age -(integer)1127.0.0.1:6379> Hset User:1sex Boy (integer)1127.0.0.1:6379> Hlen User:1(integer)3

5) batch set up or get Field-value

Command:

Hmget key field [field ...] Hmset key field value [field value ...]

Hmset and Hmget are batch setup and get Field-value,hmset required parameters are key and many pairs of field-value,hmget required parameters are key and multiple field:

127.0.0.1:6379> Hmget User:1name Age Sex1)"Kebi"2)" -"3)" Boy"127.0.0.1:6379> Hmset User:2Name Maoxian Age -Sex Boyok127.0.0.1:6379> Hmget User:2name Age Sex1)"Maoxian"2)" -"3)" Boy"

6) Determine if field exists

Command:hexists key Field

127.0. 0.1:6379> Hexists User:11127.0. 0.1:6379> Hexists User:10

If field exists, returns a result of 1 if no return 0 exists.

7) Get all the field

Command:hkeys key

The Hkeys command should be called hfields more appropriately, and it returns all field of the specified hash key:

127.0.0.1:6379> Keys *#返回所有的键1)"User:2"2)"user:1"127.0.0.1:6379> Hkeys User:1#返回键user: 1 of all field1)"name"2)" Age"3)"Sex"127.0.0.1:6379> Hkeys User:21)"name"2)" Age"3)"Sex"

8) Get all value

Command:hvals key

127.0.0.1:6379> Hvals User:11)"Kebi"2)" -"3)" Boy"127.0.0.1:6379> Hvals User:21)"Maoxian"2)" -"3)" Boy"

9) Get all the Field-value

Command:hgetall key

127.0.0.1:6379> Hgetall User:11)"name"2)"Kebi"3)" Age"4)" -"5)"Sex"6)" Boy"

Note: When using Hgetall, there is a possibility of blocking Redis if the number of hash elements is more.

If you only need to get part of the field, you can use Hmget, if you must go back to all field-value, you can use the Hscan command, which will iterate through the hash type incrementally.

Ten) Hincrby Hincrbyfloat

Command:

Hincrby Key fieldhincrbyfloat key field

The Hincrby and Hincrbyfloat commands are the same, but their scope is field.

11) Calculates the character length of value (requires Redis3.2 version or more)

Command:hstrlen key Field

The following provides the time complexity of a hash type command, which can be used to select the appropriate command according to its own requirements.

the time complexity of the hash type command

Command	Complexity of Time
Hset key field value	O (1)
Hget key Field	O (1)
Hdel key field [field ...]	O (k), K is field number
Hlen Key	O (1)
Hgetall Key	O (n), n is the total number of field
Hmget field [Field ...]	O (k), K is field number
Hmset field value [Field value ...]	O (k), K is field number
Hexists key Field	O (1)
Hkeys Key	O (n), n is the total number of field
Hvals Key	O (n), n is the total number of field
Hsetnx key field value	O (1)
Hincrby key field Increment	O (1)
Hincrbyfloat key field Increment	O (1)
Hstrlen key Field	O (1)

Understanding and use of APIs--hash type commands