Builds: add a nullable jobset_id foreign key to Jobsets.

Also, adds an explicitly named "builds" accessor to the Jobsets
Schema object, which uses the project/jobset name.

src/sql/hydra.sql

@@ -170,6 +170,7 @@ create table Builds (
     -- Info about the inputs.
     project       text not null,
     jobset        text not null,
+    jobset_id     integer null,
     job           text not null,
 
     -- Info about the build result.
@@ -236,6 +237,7 @@ create table Builds (
     check (finished = 0 or (stoptime is not null and stoptime != 0)),
     check (finished = 0 or (starttime is not null and starttime != 0)),
 
+    foreign key (jobset_id) references Jobsets(id) on delete cascade,
     foreign key (project) references Projects(name) on update cascade,
     foreign key (project, jobset) references Jobsets(project, name) on update cascade,
     foreign key (project, jobset, job) references Jobs(project, jobset, name) on update cascade

src/sql/upgrade-61.sql

@@ -0,0 +1,10 @@
+-- Add the jobset_id columns to the Builds table. This will go
+-- quickly, since the field is nullable. Note this is just part one of
+-- this migration. Future steps involve a piecemeal backfilling, and
+-- then making the column non-null.
+
+ALTER TABLE Builds
+  ADD COLUMN jobset_id integer NULL,
+  ADD FOREIGN KEY (jobset_id)
+      REFERENCES Jobsets(id)
+      ON DELETE CASCADE;