Introduce custom cache client support.

[fr33r]

Description

Introduces support for consumers of work to provide their own cache clients in the event they wish not to use the default in-memory caching. For example, users may provide clients for Redis or Memcache instead if they desire some distributed caching options.

Rationale

Depending on the use cases consumers of this library may be dealing with very large sets of data and performing large scale modifications over that data. Using an in-memory caching solution only is applicable in scenarios where the limits of how many entities to be cached is well defined and is small enough to not overwhelm the system. In all other scenarios, distributed caching is a much safer alternative.

Callouts

In order to achieve this, context.Context had to be introduced on all unit operations. This is because all of the operations would result in issuing remote calls to the cache (using the provided clients), as all operations besides Register result in deleting the corresponding entity from the cache (since it would then be classified as "dirty").

Planned Follow Ups

• Explore the ability to disable caching completely.
• Explore introducing options that automatically convert Redis and Memcache clients to UnitCacheClient.

Suggested Version

v4.0.0-beta.6

Example Usage

db := // ... database ...
cc := // ... cache client such as Redis or Memcache ...

opts = []unit.Option{
  unit.DB(db),
  unit.WithCacheClient(cc), // 🎉
}
u, err := unit.New(opts...)

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (d81ce30) 98.71% compared to head (9976548) 98.72%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #93   +/-   ##
=======================================
  Coverage   98.71%   98.72%           
=======================================
  Files          14       14           
  Lines        1399     1407    +8     
=======================================
+ Hits         1381     1389    +8     
  Misses         14       14           
  Partials        4        4           

Flag	Coverage Δ
v3	98.71% <ø> (ø)
v4	98.72% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
v4/unit.go	100.00% <100.00%> (ø)
v4/unit_cache.go	100.00% <100.00%> (ø)
v4/unit_options.go	99.58% <100.00%> (+<0.01%)	⬆️

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