3. Hash type

Introduction

Hash is similar to a small Redis database

A hash can contain multiple key-value pairs

Each key of the hash cannot be repeated and is different. Unordered arrangement

The value can be a string or a numeric value

For a numeric value, you can perform an increment or decrement operation

Hash structure

In the structure below, user represents the key name, which can contain multiple Different key-value pairs

[
    "user":[
        "name1":"yanying1",
        "name2":"yanying2",
        "name3":"yanying3"
    ]
]

How-to

Demo (Command Line + PHP Demo)

Command Line:

First, we add a key-value pair to the hash. If successful, return 1; if the key already exists, return 0

hset hash-key sub-key1 value1 // 返回 1

We add a non-existent key-value pair

hset hash-key sub-key2 value2 // 返回 1

At this time, the keys sub-key1 and sub-key2 already exist in the hash, and then we add Add an identical key sub-key1 to the hash and see what happens:

hset hash-key sub-key1 value1 // 返回 0，由于该键已经存在

Below we get the value of a given key sub-key1 through hget.

hget hash-key sub-key1 // "value1"

Successfully obtained a value. Let’s get all the added elements to see which values ​​were just added

hgetall hash-key

The results are as follows. We found that the first result is the key of the first key-value pair, the second result is the value of the key-value pair, and so on, with every two as a group.

"sub-key1""value1""sub-key2""value2"

Let’s try to delete a key. We will find that if the key previously existed in the hash, then 1 will be returned when deleting it. Otherwise, 0 will be returned.

hdel hash-key sub-key1 // 该键之前存在于散列，返回1

Let’s try to delete sub-key1 again, It is found that when deleting a non-existent key, the return result is 0

hdel hash-key sub-key1

We get all the key-value pairs again to see what is left.

hgetall hash-key

The result is that there are two less results. After all, a key-value pair has just been deleted

"sub-key1""value1"

PHP version demonstration

The first step is to link the redis database

$redis = new Redis();$redis->connect('127.0.0.1', 6379);

We first insert a key-value pair into hash-key hash. 1 means the insertion is successful; 0 element means it already exists

$redis->hset('hash-key','sub-key1','value1'); // int 1，元素插入成功，之前不存在该键

We insert the same key-value pair again

$redis->hset('hash-key','sub-key1','value1'); // int 0，元素插入失败，该键已经存在

For the following demonstration, we continue to insert some other values

$redis->hset('hash-key','sub-key2','value2'); // int 0

Now we use hget to get the value corresponding to the key. Let's try to get the value of sub-key2.

$redis->hget('hash-key','sub-key2'); // 'value2'

After getting one, we try to use hgetall to get all the values ​​​​just inserted to see which key-value pairs are contained in it

$redis->hgetall('hash-key');

The result is an array containing the complete key value

array (size=2)  'sub-key1' => string 'value1' (length=6)  'sub-key2' => string 'value2' (length=6)

After viewing all the key values Right, let's try to delete one of the keys. If the key exists in the hash before, it returns 1. Otherwise, it returns 0

$redis->hdel('hash-key','sub-key1'); // 该键之前存在，返回int 1

We try to delete the sub-key1 key again and find that it returns 0. This means that the key does not exist in the set and the deletion failed

$redis->hdel('hash-key','sub-key1'); // 该键不存在，返回int 0

Next we Use hgetall to check all key-value pairs remaining in the hash

$redis->hgetall('hash-key');

and find that only an array containing one key-value pair is returned.

array (size=1)  'sub-key2' => string 'value2' (length=6)

The reason is that sub-key1 has just been deleted