Switch to storing Git repositories in a table

Rather than just storing the URL in the guix_revisions and
load_new_guix_revision_jobs tables. This will help when storing more
information like tags and branches in the future.

guix-data-service/model/git-repository.scm

@@ -0,0 +1,58 @@
+(define-module (guix-data-service model git-repository)
+  #:use-module (ice-9 match)
+  #:use-module (squee)
+  #:export (all-git-repositories
+            git-repository-id->url
+            git-repository-url->git-repository-id
+
+            guix-revisions-and-jobs-for-git-repository))
+
+(define (all-git-repositories conn)
+  (exec-query
+   conn
+   (string-append
+    "SELECT id, label, url FROM git_repositories")))
+
+(define (git-repository-id->url conn id)
+  (match
+      (exec-query
+       conn
+       (string-append
+        "SELECT url FROM git_repositories WHERE id = $1;")
+       (list id))
+    (((url)) url)))
+
+(define (git-repository-url->git-repository-id conn url)
+  (let ((existing-id
+         (exec-query
+          conn
+          (string-append
+           "SELECT id FROM git_repositories WHERE url = '" url "'"))))
+    (match existing-id
+      (((id)) id)
+      (()
+       (caar
+        (exec-query conn
+                    (string-append
+                     "INSERT INTO git_repositories "
+                     "(url) "
+                     "VALUES "
+                     "('" url "') "
+                     "RETURNING id")))))))
+
+(define (guix-revisions-and-jobs-for-git-repository conn git-repository-id)
+  (define query
+    "
+SELECT NULL AS id, load_new_guix_revision_jobs.id AS job_id, commit, source
+FROM load_new_guix_revision_jobs
+WHERE git_repository_id = $1
+UNION
+SELECT id, NULL, commit, NULL
+FROM guix_revisions
+WHERE git_repository_id = $1
+ORDER BY 1 DESC NULLS FIRST, 2 DESC LIMIT 10;")
+
+  (exec-query
+   conn
+   query
+   (list git-repository-id)))