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views: add automatically constructed file location metadata

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When constructing views, metadata is available about the location of the
file in the view's reference branch. Allows incorporating parts of the
directory hierarchy in a view.

For example `git annex view tag=* podcasts/=*` makes a view in the form
tag/showname.

Performance impact: I benchmarked git annex view tag=* in the conference
proceedings repo to take 6.459s before this change, and 6.544s after.

FWIW, I considered making the syntax for this be podcasts/*, which might
be easier for the user to learn. However, I think it's not as good:

* The user has to then juggle two different syntaxes, and podcasts/* will
  be expanded by the shell so they also need to quote it, while podcasts/=*
  is unlikely to be expanded by the shell.
* It would allow for things like podcasts/*/* and *.mp3 which do not
  map well into views.

This commit was sponsored by Aurélien Pinceaux.
This commit is contained in:
Joey Hess 2014-02-22 16:09:00 -04:00
parent 73a5245502
commit 079b35a1a8
8 changed files with 89 additions and 25 deletions
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33
doc/tips/metadata_driven_views.mdwn
View file

@ -24,8 +24,8 @@ metadata:
# git annex metadata --tag done videos/old
# git annex metadata --tag new videos/lotsofcats.ogv
# git annex metadata --tag sound podcasts
# git annex metadata --tag done podcasts/old
# git annex metadata --tag new podcasts/recent
# git annex metadata --tag done podcasts/*/old
# git annex metadata --tag new podcasts/*/recent
So, you had a bunch of different kinds of files sorted into a directory
structure. But that didn't really reflect how you approach the files.
@ -81,9 +81,11 @@ all the way out of all views, you'll be back on the regular git branch you
originally started from. You can also use `git checkout` to switch between
views and other branches.
Beyond simple tags, you can add whatever kinds of metadata you like, and
use that metadata in more elaborate views. For example, let's add a year
field.
## fields
Beyond simple tags and directories, you can add whatever kinds of metadata
you like, and use that metadata in more elaborate views. For example, let's
add a year field.
# git checkout master
# git annex metadata --set year=2014 work/2014
@ -118,4 +120,25 @@ Oh, did you want it the other way around? Easy!
|-- 2014
`-- 2013
## location fields
Let's switch to a view containing only new podcasts. And since the
podcasts are organized into one subdirectory per show, let's
include those subdirectories in the view.
# git checkout master
# git annex view tag=new podcasts/=*
# tree -d
This_Developers_Life
Escape_Pod
GitMinutes
The_Haskell_Cast
StarShipSofa
That's an example of using part of the directory layout of the original
branch to inform the view. Every file gets fields automatically set up
corresponding to the directory it's in. So a file"foo/bar/baz/file" has
fields "/=foo", "foo/=bar", and "foo/bar/=baz". These location fields
can be used the same as other metadata to construct the view.
This has probably only scratched the surface of what you can do with views.