Posted by: AJ Welch
- Most (But Not All) Objects Use a Key
- Using Namespaces
- Retrieving All Existing Keys
Like other non-relational database engines, wrapping your mind around how Redis handles data structures and associations can sometimes be difficult. This is particularly true when Redis is compared to a more traditional relational databases with quarantined tables, each containing multiple rows and columns to house data.
Since Redis is non-relational, everything in the system is configured with basickey/valuepairs at the simplest level. During development in particular, it can be tricky to keep track of everything that exists in the database already, so in this brief tutorial we’ll cover the method for retrieving allkeysfrom a Redis database with some simple commands.
Most (but not all) objects use a key
For the vast majority of data storage with Redis, data will be stored in a simplekey/valuepair. This is best shown through theredis-cli(command line interface) usingGETandSETcommands.
For example, we may want to store some information aboutbooks, such as thetitleandauthorof a few of our favorites.
>SETtitle"TheHobbit"
OK
>SETauthor"J.R.R.Tolkien"
OKThetitleandauthorare thekeyswe’ve set and the actual string values were specified after. So we can view them withGET, like so:
>GETtitle
"TheHobbit"
>GETauthor
"J.R.R.Tolkien"
Using namespaces
That’s all well and good, but how do we add another book? We can’t reuse the sametitleandauthorkeys or we’ll overwrite the existing data. Instead, we can use namespace syntax by using a:separator and giving eachtitleorauthorentry a unique numerickey:
>SETtitle:1"TheHobbit"
OK
>SETauthor:1"J.R.R.Tolkien"
OK
>SETtitle:2"TheSilmarillion"
OK
>SETauthor:2"TheSilmarillion"
OKNow usingGETrequires adding the unique numerickeyas well:
>GETtitle:1
"TheHobbit"
>GETtitle:2
"TheSilmarillion"
Retrieving all existing keys
As it turns out, everySETcommand we issued above created a new, uniquekeywithin our Redis database. To get a list of all currentkeysthat exist, simply use theKEYScommand:
>KEYS*
1)"title:1"
2)"title:2"
3)"title"
4)"author:2"
5)"author"
6)"author:1"By followingKEYSwith an asterisk (*) – which acts as a wildcard search – we’re asking Redis to retrieve all keys in the system. Thus, we not only see our two originaltitleandauthorkeys but also the four enumerated versions that followed as well.
The syntax followingKEYScan be used to search for specific words or phrases within the key, or the exact match as well. Here we want all keys that contain the text'title':
>KEYS*title*
1)"title:1"
2)"title:2"
3)"title"CAUTION: As mentioned in the official documentation, it is advisable to avoid using theKEYScommand on very large databases, but in particular avoid using it in a production environment. SinceKEYSis returning potentially every key in the system, this can have a dramatic negative impact on performance.
