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.
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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.
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3. hmset
Set multiple field-value pairs into the hash table at the same time.
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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.
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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.
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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.
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Returns the number of successfully deleted fields, excluding ignored fields.
7. hlen
Get the number of fields in the hash table.
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8. hexists
Check whether the specified field of the hash table exists.
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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.
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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.
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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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