Redis Sorted Object Set (Sorted Hashes)

We all know that best way to store object in Redis is through, Redis hashes. And Redis sorted sets are used to keep a sorted set with a give score for each value. What if we need a sorted set of objects? What we need is a “Sorted set of Objects” . Which Redis does not support by default. We came up with a hybrid, simple data structure that a allows sorted object using Redis Hashes and Redis Sorted-sets.

Use of Redis Hashes

Here we will keep a objects as Redis hash. Think of a simple object with several values as shown below.

TICKET1 {
    MERCHANT_ID: 0123456789,
    TIME_STAMP: 00000000000,
    SALE: 12.32
}

This will be saved in the Redis as below

HMSET TICKET1 MERCHANT_ID "0123456789" TIME_STAMP "00000000000" SALE "12.32"

When we need to edit a existing value and add a new value it can be done as below

// Adding a new value
HSET TICKET1 DISCOUNT "0.60"
 
// Set Multiple Values
HMSET TICKET1 DISCOUNT "0.50" SALE "12.60"
 
// Set single Value
HSET TICKET1 SALE "12.50"
 
// RESULT
TICKET1 {
    MERCHANT_ID: 0123456789,
    TIME_STAMP: 00000000000,
    SALE: 12.50,
    DISCOUNT: 0.50
}

Getting full map and some selected value

// Get the full object
HGETALL TICKET1

1) "MERCHANT_ID" 
2) "0123456789" 
3) "TIME_STAMP" 
4) "00000000000" 
...   

// Get set of selected subset of values 
HMGET TICKET1 MERCHANT_ID SALE   
1) "0123456789" 
2) "12.50"   

// get a single value 
HGET DISCOUNT   
1) "0.50"

Whole map or items can be deleted

// Delete one field
HDEL TICKET1 SALE
 
// Delete whole object
DEL TICKET1

There is some more commands in the Redis hash that can help us in this process

HEXISTS	Check for item
HINCRBY	Add to integer value
HINCRBYFLOAT	Add to float value
HKEYS	Return all keys
HLEN	Get number of items
HSCAN	Iterate items
HSETNX	Set item if doesn’t exist
HVALS	Return all values

Use of Redis Sorted Sets

As we said above we need to search with time values and in-order searches. This cannot be done alone by Redis hashes. Here we keep a list of all keys in the Redis hashes as a sorted set. This allow us to get all the maps that came after some time stamp. or between two time stamps. Other than that this allows us to search under topics (EX: get all TICKETS after 00000001 time stamp)

ZADD TICKETS 1459746182 "TICKET1"
ZADD TICKETLINES 1459746192 "TICKETLINE1"
ZADD TICKETLINES 1459746222 "TICKETLINE2"
ZADD TICKETS 1459746282 "TICKET2"
ZADD TICKETS 1459746382 "TICKET3"

Get items under one topic within a given time range

ZRANGE TICKETS 1459746282 -1
1) "TICKET2"
2) "TICKET3"

There is some more commands in the Redis hash that can help us in this process

ZCARD	Get number of items
ZCOUNT	Number of items within score range
ZINCRBY	Add to score
ZLEXCOUNT	Lexico­gra­phical range count
ZRANGE	Get items within rank range
ZLEXRANGE	Get items within lexico­gra­phical range
ZRANGEBYSCORE	Get items within score range
ZRANK	Get item rank
ZREM	Remove item(s)
ZREMRANGEBYLEX	Remove items within lexico­gra­phical range
ZREMRANGEBYRANK	Remove items within rank range
ZREMRANGEBYSCORE	Remove items within score range
ZREVRANGE	ZRANGE in reverse order
ZREVRANGEBYSCORE	ZRANGE­BYSCORE in reverse order
ZREVRANK	ZRANK in reverse order
ZSCAN	Iterate items
ZSCORE	Get item score
ZUNIONSTORE	Store union

 

Last updated by Romesh Maling Perera.