Settings View Source Streaming Caches

Cachex provides the ability to return an Elixir Stream based on the contents of a cache, which is built using a table cursor and Stream.resource/3. This allows you to use any of the Enum or Stream module functions on the entries in a cache, which can be very powerful. By default, Cachex.stream/3 will return a stream over all entries in a cache which are yet to expire (at the time of stream creation). They will be streamed as entry() records, and you can match and do all of the typical record stuff to them assuming you have Cachex.Spec imported:

# for matching
import Cachex.Spec

# store some values in the cache
Cachex.put(:my_cache, "one", 1)
Cachex.put(:my_cache, "two", 2)
Cachex.put(:my_cache, "three", 3)

# 6
:my_cache
|> Cachex.stream!
|> Enum.reduce(0, fn(entry(value: value), total) ->
    total + value
   end)

complex-streaming

Complex Streaming

While the Enum module provides the ability to filter records easily, you can optimize using a match specification. This is a match specification as defined by the Erlang documentation (Cachex does little modification here), and can be passed as the second argument to Cachex.stream/3 to filter. For your convenience, Cachex.Query exposes a few functions designed to assist with query creation. If we take the example above, we can use a query to only sum the odd numbers, without having to filter on the Elixir side, where it would be slower:

# for matching
import Cachex.Spec

# store some values in the cache
Cachex.put(:my_cache, "one", 1)
Cachex.put(:my_cache, "two", 2)
Cachex.put(:my_cache, "three", 3)

# generate our filter to find odd values
filter = { :==, { :rem, :value, 2 }, 1 }

# generate the query using the filter
query = Cachex.Query.create(filter, :value)

# 4
:my_cache
|> Cachex.stream!(query)
|> Enum.sum

Couple of things to mention here; first of all, you can use any of the entry() field names in your matches, and they'll be substituted out automatically. In this case we use :value in our filter, which would compile down to :"$4" instead. You might also have noticed that we can jump directly to Enum.sum/1 here. The second (optional) argument to create/2 controls the format of the stream elements, in this case just streaming the :value field of the entry. If the second argument is not provdided, it'll stream entry records (just like the first example). It should be noted that Cachex.Query.create/2 will automatically bind a filter clause to filter out expired documents. If you wish to run a query on the entire dataset, you can use Cachex.Query.raw/2 instead.