=head1 NAME

DBIx::Class::Migration::FAQ - Answers to Frequently Asked Questions

=head1 When I run the commandline, I see a lot of debugging output

    SV = IV(0x7fb4e24dc858) at 0x7fb4e24dc868
      REFCNT = 1
      FLAGS = (ROK,READONLY)
      RV = 0x7fb4e0b0ddf8
        SV = PVHV(0x7fb4e24c48a0) at 0x7fb4e0b0ddf8
          REFCNT = 1
          FLAGS = (OBJECT,SHAREKEYS)
          STASH = 0x7fb4e2174a80	"DBI::db"
          ARRAY = 0x0
          KEYS = 0
          FILL = 0
          MAX = 7
          RITER = -1

There's some debugging code somewhere in the L<DBIx::Class::DeploymentHandler>
dependency chain.  We've looked and can't find it :(  A case of beer at the
next YAPC we meet at to whoever can figure it out.

Although if you see this, there's nothing wrong.  The command will work as in
the documentation.  The only issue is that if there's a lot of debugging scroll
by, you might need to page up in your terminal to catch any real error
messages.

B<UPDATE>:  I recieved an email from a contributor who has code dived a bit
and possibly narrowed down the issue.  I thought to report that stuff here.
When L<SQLT::Parser::DBIx::Class> attempts to serialize schemas that are connected
it trys to serialize the connect object information.  This doesn't play so nice
with the way the YAML serializer works, since it does try hard to serialize
objects.

More details in the RT

    ticket: https://rt.cpan.org/Public/Bug/Display.html?id=75394

A possible fix is to change SQLT::Parser::DBIx::Class so that it doesn't try
to serialize that object.  I think this could be a good fix since I don't
think we can properly de serialize a DBI connection reliably.  

=head1 Contributing

Contributing to the project is easy.  First you'd fork the project over at
Github (L<https://github.com/jjn1056/DBIx-Class-Migration>), clone the repo
down to your work environment and install project dependencies:

    cpanm Dist::Zilla
    dzil authordeps | cpanm
    dzil listdeps | cpanm

You should first have a Modern Perl setup, including L<local::lib>.  If you
need help installing Perl and getting started, please take a look at the
Learning Perl website: L<http://learn.perl.org/installing/>

=head1 Dist::Zilla?

I realize L<Dist::Zilla> seems to invoke feelings on nearly religious vigor
(both for and against).  After considering the options I felt using it, but
carefully constraining the use of plugins to the default set was a better
option than what I've done on other projects, which is to have a custom wrapper
on top of L<Module::Install> (you can peek at that if you want over here:
L<https://github.com/jjn1056/Maker>).  I've decided I'd rather not
continue to spend my limited time dealing with dependency and installation
management tools, when there's a rational solution that many people already
embrace available. The only other option is to continue to build and maintain
code for this purpose that nobody else uses, and possibly nobody else
understands.

If a better option with equal or greater maturity and community acceptance
emerges, I'll entertain changing.

If the requirement of typing C<cpanm Dist::Zilla> and using the C<dzil> command
line tool for a limited number of build jobs prevents you from contributing,
I think you are unreasonably stubborn.

If you do contribute to the project, please be aware that I'm not likely to
accept patches that include significant changes to the way I'm using
L<Dist::Zilla>, including using plugins to weave pod, automagically guess
dependencies and generate tests.  I'd prefer to stick to the most simple and
standard Perl practices for building and installing code for the present.

=head1 I don't want my database sandbox files in my source control repository

Having the database sandboxes automatically created in the C<share> directory
is a nice feature, but can clutter your repository history.  You really don't
need that in the source control, since installing and controlling your database
is something each developer who checks out the project should do.

If you are using C<git> you can modify your C<.gitignore>.  If you sandbox is
C<share/myapp-schema.db> or (if you are using the mysql or postgresql sandboxes)
C<share/myapp-schema/> you can add these lines to your C<.gitignore>

    share/musicbase-schema/*
    share/musicbase-schema.db

Other source control systems have similiar approaches (recipies welcome for 
sharing).

=head1 What's the command to run migrations on an existing database?

    dbic-migration -Ilib status \
      --dsn="DBI:mysql:database=test;host=127.0.0.1;port=5142" \
      --user msandbox \
      --password msandbox

Would be the general approach.

=head1 Error: Trouble creating a MySQL Sandbox when running AppArmor

Its been reported that the developer database sandboxing feature doens't
work properly when using AppArmor.  I guess AppArmor considers this a 
security violation.  Currently I don't have a reported workaround other than
to just disable AppArmor, which for developer level machines may or may not
be a problem.

Here's some symptoms of this problem, if you think you may be having it:

In C</var/log/syslog> something like:

    kernel: [18593519.090601] type=1503 audit(1281847667.413:22):
    operation="inode_permission" requested_mask="::r" denied_mask="::r"
    fsuid=0 name="/etc/mysql0/my.cnf" pid=4884 profile="/usr/sbin/mysqld"

If you need AppArmor, you'll have to setup and install MySQL the 'old school
way.'

=head1 Error: "Failed to find share dir for dist..."

You didn't specify a custom C<--target_dir> but forgot to make the C</share>
directory in your project application root.

By default we expect to find a C</share> directory in your primary project root
directory (contains your C<Makefile.PL> or C<dist.ini>, and the C<lib> and C<t>
directories for example) where we will create migrations.  At this time we can't
automatically create this C</share> directory in the same way we can create all
the migration files and directory for you.  You need to create that directory
yourself:

    mkdir share

Patches to fix this, or suggestions welcomed.

=head1 Can I use this even if I don't want to use DBIx::Class?

Not everyone loves using an ORM.  Personally I've found L<DBIx::Class> to be
the only ORM that gets enough out of my way that I prefer it over plain SQL,
and I highly recommend you give it a go.  However if you don't want to, or can
not convince your fellow programers (yet :) ), here's one way to still use this
migrations and fixtures system.  Strictly speaking, we are stilling using
L<DBIx::Class> behind the scenes, just you don't have to know about it or
use it.

You use a subclass of L<DBIx::Class::Schema::Loader> in a namespace for your
application, like:

    package MyApp::Schema;

    use strict;
    use warnings;

    use base 'DBIx::Class::Schema::Loader';

    our $VERSION = 1;

    __PACKAGE__->naming('current');
    __PACKAGE__->use_namespaces(1);
    __PACKAGE__->loader_options( );

    1;

You'd put that in C<lib/MyApp/Schema.pm> along with your other application code.
then just use C<MyApp::Schema> as is discussed in the documentation.  This will
dynamically build a schema for you, as long as you set the schema arguments to
connect to your actual database.  Then everytime someone changes the database
you just up the C<$VERSION> and take it from there.  Obviously this is a bit
more manual effort, but at least you can have the ability to populate to any
given version, manage fixtures, do some sane testing, etc.  Maybe you'll even
be able to convince people to try out L<DBIx::Class>!

By the way, if you wanted, you can always dump the generated version of your
classes using C<make_schema> (see L<DBIx::Class::Migrations/make_schema> and
L<DBIx::Class::Migrations::Script/make_schema>).

=head1 I am using MySQL and when the migration fails, it doesn't ROLLBACK

That's because MySQL does not support transaction DDL.  Even if you have a
transaction, MySQL will silently COMMIT when it bumps into some DDL.

=head1 I need to dump fixtures from a existing database

You don't always have the luxury of building a new database from the start.
For example, you may have an existing database that you want to start to
create migrations for.  In this case you probably want to dump some data
directly from that existing database in order to create fixtures for testing
or for seeding a new database.

L<DBIx::Class::Migration> will let you run the C<dump_all_sets> and C<dump_named_sets>
commands against an unversioned database.  For example:

    dbic-migration -Ilib -SMyApp::Schema dump_all_sets /
      --dsn="dbi:mysql:database=myapp;host=10.0.88.98;port=3306" /
      --username johnn /
      --password $PASSWORD

In this case let's say "dbi:mysql:database=myapp;host=10.0.88.98;port=3306" is
a database that you've been managing manually and it has some data that is useful
for creating your fixture sets.

When you run these commands against an unversioned database you will be warned
because we have no way of being sure what version of the fixture sets you should
be dumping.  We will just assume that whatever the Schema version is, is correct.
This can of course lead to bad or undumpable fixtures should your Schema and the
unversioned DB not match properly.  Buyer beware!

=head1 Error: "`' is not a module name"

Sorry this error is vague and I am working on a fix.  You will get this if you
have failed to provide a C<schema_class>, either by setting it with the -S or
-schema_class commandline option flag:

    dbic-migration -Ilib -SMyApp::Schema
    dbic-migration -Ilib --schema_class MyApp::Schema

or by exporting the %ENV:

    export DBIC_MIGRATION_SCHEMA_CLASS=MyApp::Schema

Or, if you have a custom version of L<DBIx::Class::Migration::Script> as
discussed in the tutorial, you are not providing a good C<schema_class> value.

=head1 Error: "Attribute (schema_class) does not pass the type constraint"

You probably forgot to include your project C<lib> directory in the Perl search
path.  The easiest way to fix this is to use the C<I> or C<lib> command line:
option flag:

    dbic-migration -Ilib -SMyApp::Schema [command]

=head1 When using the Postgresql Sandbox, I get "FATAL: could not create shared memory segment"

There will be more like this:

    FATAL:  could not create shared memory segment: Cannot allocate memory
    DETAIL:  Failed system call was shmget(key=1, size=2138112, 03600).
    HINT:  This error usually means that PostgreSQL's request for a shared memory
    segment exceeded available memory or swap space, or exceeded your kernel's 
    SHMALL parameter.  You can either reduce the request size or reconfigure 
    the kernel with larger SHMALL.  To reduce the request size (currently 2138112
    bytes), reduce PostgreSQL's shared memory usage, perhaps by reducing 
    shared_buffers or max_connections.

The solution is as presented.  Since I prefer not to change my system settings
permanently, just add the following to a little bash script in my application

    sudo sysctl -w kern.sysv.shmall=65536
    sudo sysctl -w kern.sysv.shmmax=16777216

I don't know enough about Postgresql to know if the above settings are good,
but they work for my testing.  Corrections very welcome!  Ideally I'd try to
find a way to offer a patch to L<Test::postgresql>, although this seems to be
limited to people using Macs.

=head1 How to Release

Here's the release steps I currently use, should I eventually find willing
comainters:

=over4

=item Update Version

You need to increment the version in C<dist.ini> and in L<DBIx::Class::Migration>

=item Prepare Changes file

Update the C<Changes> file.  It would be ideal to have been adding to this as
you've gone along, but you should double check.

=item Update Author's list

If there have been new contributors, be sure to give credit

=item Rebuild the README

    pod2markdown < lib/DBIx/Class/Migration.pm > README.mkdn

This will make sure the C<README.mkdn> file in the project root matches the most
recent updates.

=item Check your tests

    AUTHOR_MODE=1 prove -lvr t

=item Update the repository

    git add @stuff_to_add
    git commit -m $message
    git push

=item Make the Distribution

    dzil build
    dzil release
    dzil clean

=item Update the git version tag

I usually don't update and push the tag until we are on CPAN.

    git tag $VERSION -m 'cpan release'
    git push --tags

=back

=head1 AUTHOR

See L<DBIx::Class::Migration> for author information

=head1 COPYRIGHT & LICENSE

See L<DBIx::Class::Migration> for copyright and license information

=cut


