Complete Intro to Databases v2

Redis has a few different types of data. We won't go over all of them because most of them cover more advanced use cases, but so you know, here they are:

• Strings (binary safe, so you could write the contents of JPEG here)
  • Technically numbers/integers are implemented as strings
• Lists (i.e. arrays)
• Sets
• Sorted sets (similar to above but everything has a "score" to it so you can grab the top ten values. Think priority queue sort of idea)
• Hashes (think JS object or Python hash)

You've already seen a string. Try running

SET name Brian
TYPE name # string
SET visits 10
TYPE visits # string

Lists

I don't find myself frequently needing lists with Redis, but a good use case may be notifications for a user. Let's say you have a user that has three notifications you need to add.

RPUSH notifications:btholt "Call your mom" "Feed the dog" "Take out trash"
LRANGE notifications:btholt 0 -1

• RPUSH can be thought of as a push on a stack. You're adding thing(s) to the end of a list.
• LRANGE can be thought of as the GET for lists (GET doesn't work on lists). It always requires the indexes you want to get so 0 -1 gets you the whole list. You can give it 1 5 and that will be the 1 index (i.e. the second) element to the 5 index element. Negative numbers count back from the end with -1 being the last element, -2 being the penultimate, etc.

Okay, so let's say btholt dismisses the last item on the list. You could do:

RPOP mylist

• This, like pop on stack, will return the last item on the list and remove it from the list.
• LPOP does the same from the front of the list.
• LPUSH also works as well, adding items to the front.
• LTRIM allows you to truncate a list. If I said LTRIM notifications:btholt 0 5 it'd drop any notifications beyond five. This is useful if we don't let btholt get any more than five notifications at a time.

Hashes

Think of hashes like an object in Redis. Maybe we could represent btholt's user like this:

HSET btholt:profile title "principal program manager" company "Microsoft" city "Seattle" state "WA"
HGET btholt:profile city
HGETALL btholt:profile

Useful if we don't want to have separate keys for all of these. Do note that most of the operators like INCR exist for hashes as well e.g. HINCRBY. See here.

Sets and Sorted Sets

A set is just a group of things. In our case it will be a group of strings which won't have a concept of order. For example, if you had a set of colors. There's no "order" to a set of colors, it's just a group. We could do this:

SADD colors red blue green yellow
SMEMBERS colors
SISMEMBER colors green # true
SISMEMBER colors gold # false
SPOP colors # removes and returns a random element

Redis actually returns 1 for true and 0 for false.

There's another sort of set that's called a sorted set that allows you to add priorities so that you can ask for the top ten things in a list. We won't spend a lot of time on them, but here's a quick demonstration:

ZADD ordinals 3 third
ZADD ordinals 1 first
ZADD ordinals 2 second
ZADD ordinals 10 tenth
ZRANGE ordinals 0 -1

It's basically an array that sorts itself on the fly based on those priorities you give to it.

If you're keen to learn more see here.

JSON

A small note on the JSON type here - most of what you would use JSON for is covered by the other data types. A lot of times I'll just store the raw JSON string as a string because I don't need Redis to operate on the object, just retrieve it when asked. And when I do need more than that, hashes and sets usually cover those cases. But if you need to actually store a JSON object and be able to access properties on the object, there is the JSON type. I've never actually used it in production.

See the docs for more details.

Lots More

I picked a few interesting ones. See more types here.