Database.VCache.Path

Documentation

vcacheSubdir :: ByteString -> VCache -> VCache

VCache implements a simplified filesystem metaphor. Developers can assign a distinct prefix for all PVars created by the VCache, thus modeling namespaces or subdirectories. Assuming the normal advice of opening the VCache only once in the main module, these prefixes enable transparent, modular decomposition of a VCache application without risk of name collisions.

VCache is simplistic about this: a prefix is appended directly. If developers use subdir "foo" followed by "bar", the result is the same as "foobar". Separators are left to local conventions. Consider "foo" and "bar" to model filesystem subdirectories.

Paths have a limited maximum size of ~500 bytes, including the final PVar name. A runtime error may be generated for oversized paths. In practice, this should not be an issue.

Usage Note: Subdirectories allow developers to control risk of namespace collisions between modules or plugins. But they are not intended for domain data! Avoid dynamically creating directories or named PVars based on runtime data. It's better to push most domain logic and schema into the PVar layer, which is subject to rich type safety, GC, potential versioning, and other benefits.

vcacheSubdirM :: ByteString -> VCache -> Maybe VCache

as vcacheSubdir, but returns Nothing if the path is too large.