concept HASH in category redis
This is an excerpt from Manning's book Redis in Action.
Whereas LISTs and SETs in Redis hold sequences of items, Redis HASHes store a mapping of keys to values. The values that can be stored in HASHes are the same as what can be stored as normal STRINGs: strings themselves, or if a value can be interpreted as a number, that value can be incremented or decremented. Figure 1.4 shows a diagram of a hash with two values.
In a lot of ways, we can think of HASHes in Redis as miniature versions of Redis itself. Some of the same commands that we can perform on STRINGs, we can perform on the values inside HASHes with slightly different commands. Try to follow listing 1.4 to see some commands that we can use to insert, fetch, and remove items from HASHes. Table 1.6 describes the commands.
Table 1.6. Commands used on HASH values
Command
What it does
HSET Stores the value at the key in the hash HGET Fetches the value at the given hash key HGETALL Fetches the entire hash HDEL Removes a key from the hash, if it exists For those who are familiar with document stores or relational databases, we can consider a Redis HASH as being similar to a document in a document store, or a row in a relational database, in that we can access or change individual or multiple fields at a time. We’re now one structure from having seen all of the structures available in Redis. Keep reading to learn what ZSETs are and a few things that we can do with them.
If you remember from chapter 3, the Redis SORT call allows us to sort the contents of a LIST or SET, possibly referencing external data. For each article in Fake Garage Startup’s knowledge base, we’ll also include a HASH that stores information about the article. The information we’ll store about the article includes the title, the creation timestamp, the timestamp for when the article was last updated, and the document’s ID. An example document appears in figure 7.4.
