Re: [Monotone-devel] Multiple projects in one database -- branch confusion

[Justin Patrin]

On 12/6/06, Steven E. Harris <address@hidden> wrote:
> Even after using monotone for a while, I'm still confused about how to
> keep multiple projects in a single database. Or, rather, I'm confused
> about what happens when one attempts to mix and merge content from
> separate branches that don't share ancestry.
>
> Say that I start a branch "project.experiment" in my database with
> this file structure:
>
> ,----[ project.experiment ]
> | ./
> | | one.txt
> | | two.txt
> | +-dir/
> |     three.txt
> `----
>
> Later, I start another branch afresh called "project.prototype" in the
> same database with this file structure:
>
> ,----[ project.prototype ]
> | ./
> |   one.txt
> |   four.txt
> `----
>
> These two projects on separate branches were conceived as being
> independent, but now I realize that I'd like to combine them into a
> single source tree (maybe also moving some things around).
>
> Does monotone see any relationship between the two files "./one.txt"?
> They are in the same place with the same name with respect to some
> root directories, but at their conception these two roots had nothing
> to do with one another.

Monotone won't see any relationship until you merge one into the
other. Then it will get a mege conflict when you try to merge them as
they're named the same but do no share any ancestry. This is if you
simply merge them as-is, though.

One way to merge these would be to use merg_into_dir. This allows you
to merge one branch's root into a directory in another branch. So
you'd do:

mtn --db=db.MTN merge_into_dir project.experiment project.prototype experiment

and you'd get:

,----[ project.prototype ]
| ./
|   one.txt
|   four.txt
| +-experiment/
|    one.txt
|    two.txt
|   +-dir/
|      three.txt
`----

> Is it possible to merge these two branches? One idea I had to avoid
> naming conflicts was to first move most of the content of one branch
> under some new root directory, then try merging that into the other
> tree to at least get all the files together in the same branch.

This may work, but may also cause merge conflicts as the same named
file will have been moved in one branhc but not in another. I'm not
sure of this, though. If you're going to do it this way merge_into_dir
is likely your best bet.

> Obviously, I'm confused about whether a single database can hold many
> separate directory trees (with overlapping names), or if all the
> branches are just different views of the same shared tree.

They are only "shared" if they have shared ancestry. If you have 2
branches which were not proagated/branched to/from each other then
they are different. If one was branched from another then merging back
in will use the ancestry to try to merge intelligently.

> What got me thinking about this is the "deleted stays deleted"
> rule. If in my "project.experiment" branch I had at one time created
> then discarded a file "five.txt", but I've started using a file in the
> "project.prototype" branch also called "five.txt", would merging the
> former branch into the latter delete "five.txt" permanently, even
> though they were really separate files to begin with?

No, it would cause a merge conflict since they do not have shared ancestry.

--
Justin Patrin