# Hash

Redis hashes are record types structured as collections of field-value pairs. You can use hashes to represent basic objects and to store groupings of counters, among other things.

* [`HSET`](https://redis.io/commands/hset) sets the value of one or more fields on a hash.
* [`HGET`](https://redis.io/commands/hget) returns the value at a given field.
* [`HMGET`](https://redis.io/commands/hmget) returns the values at one or more given fields.
* [`HINCRBY`](https://redis.io/commands/hincrby) increments the value at a given field by the integer provided.

```
HSET "product:501" title "Laptop" price "799" description "Latest model..." stock "150"

(Retrieve title and price for the product)
HMGET "product:501" title price stock

(Decrement stock by 1 when a product is purchased)
HINCRBY "product:501" stock -1 

HMGET "product:501" title price stock

HGETALL "product:501"

HDEL "product:501" "stock"
```

### Use Case: User Session Store

| userid | 1             |
| ------ | ------------- |
| name   | Rachel        |
| ip     | 10.20.133.233 |
| hits   | 1             |

```
HSET usersession:1 userid 1 name Rachel ip 10.20.133.233 hits 1

# One Value
HGET usersession:1 hits

# Multiple Values
HMGET usersession:1 userid name ip hits

# Increment
HINCRBY usersession:1 hits 1

HDEL usersession:1 hits

# What happens when you GET the deleted key?

HMGET usersession:1 userid name ip hits
```

**EXPIRE**

Sets a Key's time to live (TTL). The key will be automatically deleted from Redis once a specific duration (in seconds) has elapsed.

```
EXPIRE usersession:1 10
```

**DEL**

Immediately deletes a key and its associated value from Redis

```
DEL usersession:1
```