feat(content): support useCache option

[kwiatkk1]

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

When you have a large number of content files (100+), app startup slows down a lot. It hurts in a development mode (see #694 and #767), but also when you deploy a built app onto a production server.

My proposal is to:

• during build, if target is server: to serialize content's db into a file
• during startup, if not in dev mode: do not walk through content's dir and parse found files, but to load content from a file generated during build

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes (if not applicable, please state why)

[kwiatkk1]

It's in a draft, because:

• it breaks existing tests
• it hasn't got its own tests

But I hope it shows the general idea. I hope you can look at it and say is it something you want to have in the product?
If so, I'll refine this pull-request.

[pi0]

Hi @kwiatkk1 thanks for PR! I think it would be really good idea to use hard-cache to reduce development startup time. I would suggest moving logic load logic into Database.init and use an option to enable hard-cache by constructor or init (maybe cache: true). Also i think we should use generate:done hook since with full-static smart rebuild, we only generate content second time (which needs fresh parsed data)

[kwiatkk1]

Hi @pi0, I made some changes:

• logic hidden behind the useCache flag,
• tests,
• sketch of documentation.

This feature doesn't apply to developer mode or the full static generate -- production build only -- I have no idea how to make it work with content reloading :/

[nozomuikuta]

@kwiatkk1

Your PR has been merged as Nuxt Content v1.15.0!
Thank you so much!