Analysis of common operation examples of Hash, the basic data type of Redis

Redis data type Hash common operations

In Redis, the hash table is a data structure that maps string type fields and corresponding values. Particularly suitable for storing objects, each hash can store more than 4 billion key-value pairs.

Children's shoes who are familiar with python can think of it as a dictionary dict. The previous data type storage was k-v, and the hash storage is k-dict, and dict will have its own k-v.

1. hset

Assign values ​​to the fields in the hash table. If the hash table does not exist, create a new hash table and perform the hset operation.
If the field already exists in the hash table, the old value will be overwritten.

hset myhash k1 v1

2. hget

Returns the value of the specified field in the hash table. If the given field or key does not exist, nil is returned.

hget myhash k1

3. hmset

Set multiple field-value pairs into the hash table at the same time.

hmset myhash k2 v2 k3 v3

If the field already exists in the hash table, it will be overwritten.
If the hash table does not exist, an empty hash table will be created and the hset operation will be performed.

4. hmget

Returns the value of one or more given fields in the hash table.

hmget myhash k1 k2 k3 k4

If the specified field does not exist in the hash table, then a nil value is returned.

5. hgetall

Returns all fields and values ​​in the hash table.

hgetall myhash

Note that in the return value, immediately following each field name (field name) is the value of the field (value), so the length of the return value is twice the size of the hash table.

6. hdel

Delete one or more specified fields in the hash table key. Non-existing fields will be ignored.

hdel myhash k2 k3 k5

Returns the number of successfully deleted fields, excluding ignored fields.

7. hlen

Get the number of fields in the hash table.

hlen myhash

8. hexists

Check whether the specified field of the hash table exists.

hexists myhash k1

If the hash table contains the given field, return 1.
If the hash table does not contain the given field, or key does not exist, return 0.

9. hkeys

Get all fields in the hash table.

hkeys myhash

Contains a list of all fields in the hash table. When key does not exist, an empty list is returned.

10. hvals

Returns the values ​​of all fields in the hash table.

hvals myhash

Returns a list containing all field values ​​in the hash table. When key does not exist, an empty table is returned.

11. hincrby

Adds the specified increment value to the field value in the hash table. This increment can also be a negative number, which is equivalent to Subtraction.

If the key of the hash table does not exist, create a new hash table and execute the hincrby command.

If the specified field does not exist, the value of the field will be initialized to 0 before executing the command.

If executed on a field that stores a string value, an error will be reported.

12. hsetnx

Assign values ​​to fields that do not exist in the hash table.

If the hash table does not exist, create a new hash table and perform hset operation.

If the field already exists in the hash table, the operation is invalid.

If the key does not exist, create a new hash table and execute the hsetnx command.

Regarding the application of hash in redis, such as saving user information data and frequently changing information, if you do not want to use traditional k-v objects to store, you can use redis hash.

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