dependencies.diff

diff --git a/lib/Minion/Backend/Pg.pm b/lib/Minion/Backend/Pg.pm
index c6e0ad2..b298c51 100644
--- a/lib/Minion/Backend/Pg.pm
+++ b/lib/Minion/Backend/Pg.pm
@@ -29,11 +29,12 @@ sub enqueue {
 
   my $db = $self->pg->db;
   return $db->query(
-    "insert into minion_jobs (args, attempts, delayed, priority, queue, task)
-     values (?, ?, (now() + (interval '1 second' * ?)), ?, ?, ?)
+    "insert into minion_jobs
+       (args, attempts, delayed, parents, priority, queue, task)
+     values (?, ?, (now() + (interval '1 second' * ?)), ?, ?, ?, ?)
      returning id", {json => $args}, $options->{attempts} // 1,
-    $options->{delay} // 0, $options->{priority} // 0,
-    $options->{queue} // 'default', $task
+    $options->{delay} // 0, $options->{parents} || [],
+    $options->{priority} // 0, $options->{queue} // 'default', $task
   )->hash->{id};
 }
 
@@ -42,12 +43,14 @@ sub finish_job { shift->_update(0, @_) }
 
 sub job_info {
   shift->pg->db->query(
-    'select id, args, attempts, extract(epoch from created) as created,
+    'select id, args, attempts,
+       array(select id from minion_jobs where j.id = any(parents)) as children,
+       extract(epoch from created) as created,
        extract(epoch from delayed) as delayed,
-       extract(epoch from finished) as finished, priority, queue, result,
-       extract(epoch from retried) as retried, retries,
+       extract(epoch from finished) as finished, parents, priority, queue,
+       result, extract(epoch from retried) as retried, retries,
        extract(epoch from started) as started, state, task, worker
-     from minion_jobs where id = ?', shift
+     from minion_jobs as j where id = ?', shift
   )->expand->hash;
 }
 
@@ -120,6 +123,17 @@ sub repair {
   )->hashes;
   $fail->each(sub { $self->fail_job(@$_{qw(id retries)}, 'Worker went away') });
 
+  # Jobs with missing parents
+  $db->query(
+    "update minion_jobs as j
+     set finished = now(), result = to_json('Parent went away'::text),
+       state = 'failed'
+     where state = 'inactive' and parents != '{}'
+       and array_length(parents, 1) != (
+       select count(*) from minion_jobs where id = any(j.parents)
+     )"
+  );
+
   # Old jobs
   $db->query(
     "delete from minion_jobs
@@ -152,7 +166,7 @@ sub stats {
     "select state::text || '_jobs', count(*) from minion_jobs group by state
      union all
      select 'delayed_jobs', count(*) from minion_jobs
-     where state = 'inactive' and delayed > now()
+     where state = 'inactive' and (delayed > now() or parents != '{}')
      union all
      select 'inactive_workers', count(*) from minion_workers
      union all
@@ -187,9 +201,12 @@ sub _try {
     "update minion_jobs
      set started = now(), state = 'active', worker = ?
      where id = (
-       select id from minion_jobs
+       select id from minion_jobs as j
        where delayed <= now() and queue = any (?) and state = 'inactive'
-         and task = any (?)
+         and task = any (?) and (parents = '{}' or array_length(parents, 1) = (
+           select count(*) from minion_jobs as p
+           where p.id = any(j.parents) and p.state = 'finished'
+         ))
        order by priority desc, created
        limit 1
        for update skip locked
@@ -759,3 +776,6 @@ create trigger minion_jobs_notify_workers_trigger
 -- 9 down
 drop trigger if exists minion_jobs_notify_workers_trigger on minion_jobs;
 drop function if exists minion_jobs_notify_workers();
+
+-- 10 up
+alter table minion_jobs add column parents bigint[] default '{}'::bigint[];
diff --git a/t/pg.t b/t/pg.t
index 1a1e7ef..65945b2 100644
--- a/t/pg.t
+++ b/t/pg.t
@@ -24,10 +24,11 @@ my $worker = $minion->repair->worker;
 isa_ok $worker->minion->app, 'Mojolicious', 'has default application';
 
 # Migrate up and down
-is $minion->backend->pg->migrations->active, 9, 'active version is 9';
+is $minion->backend->pg->migrations->active, 10, 'active version is 10';
 is $minion->backend->pg->migrations->migrate(0)->active, 0,
   'active version is 0';
-is $minion->backend->pg->migrations->migrate->active, 9, 'active version is 9';
+is $minion->backend->pg->migrations->migrate->active, 10,
+  'active version is 10';
 
 # Register and unregister
 $worker->register;
@@ -194,8 +195,10 @@ like $batch->[0]{created}, qr/^[\d.]+$/, 'has created timestamp';
 is $batch->[1]{task},      'fail', 'right task';
 is_deeply $batch->[1]{args}, [], 'right arguments';
 is_deeply $batch->[1]{result}, ['works'], 'right result';
-is $batch->[1]{state},      'finished',   'right state';
-is $batch->[1]{priority},   0,            'right priority';
+is $batch->[1]{state},    'finished', 'right state';
+is $batch->[1]{priority}, 0,          'right priority';
+is_deeply $batch->[1]{parents},  [], 'right parents';
+is_deeply $batch->[1]{children}, [], 'right children';
 is $batch->[1]{retries},    1,            'job has been retried';
 like $batch->[1]{created},  qr/^[\d.]+$/, 'has created timestamp';
 like $batch->[1]{delayed},  qr/^[\d.]+$/, 'has delayed timestamp';
@@ -593,6 +596,37 @@ is $minion->job($id4)->info->{result}, 'Non-zero exit status (1)',
   'right result';
 $worker->unregister;
 
+# Job dependencies
+$worker = $minion->worker->register;
+$id     = $minion->enqueue('test');
+$id2    = $minion->enqueue('test');
+$id3    = $minion->enqueue(test => [] => {parents => [$id, $id2]});
+is $minion->stats->{delayed_jobs}, 1, 'one delayed job';
+$job = $worker->dequeue(0);
+is $job->id, $id, 'right id';
+is_deeply $job->info->{children}, [$id3], 'right children';
+is_deeply $job->info->{parents}, [], 'right parents';
+$job2 = $worker->dequeue(0);
+is $job2->id, $id2, 'right id';
+is_deeply $job2->info->{children}, [$id3], 'right children';
+is_deeply $job2->info->{parents}, [], 'right parents';
+ok !$worker->dequeue(0), 'parents are not ready yet';
+$job->finish;
+ok !$worker->dequeue(0), 'parents are not ready yet';
+$job2->finish;
+$job = $worker->dequeue(0);
+is $job->id, $id3, 'right id';
+is_deeply $job->info->{children}, [], 'right children';
+is_deeply $job->info->{parents}, [$id, $id2], 'right parents';
+$id = $minion->enqueue(test => [] => {parents => [-1]});
+ok !$worker->dequeue(0), 'job with missing parent will never be ready';
+$minion->repair;
+like $minion->job($id)->info->{finished}, qr/^[\d.]+$/,
+  'has finished timestamp';
+is $minion->job($id)->info->{state}, 'failed', 'job is no longer active';
+is $minion->job($id)->info->{result}, 'Parent went away', 'right result';
+$worker->unregister;
+
 # Clean up once we are done
 $pg->db->query('drop schema minion_test cascade');