Automatically insert crate_downloads row on crates table insert

Author: Turbo87

migrations/2024-03-04-092044_crate-downloads-table/down.sql

@@ -1 +1,3 @@
+drop trigger insert_crate_downloads_row on crates;
+drop function insert_crate_downloads_row;
 drop table crate_downloads;

migrations/2024-03-04-092044_crate-downloads-table/up.sql

@@ -1,3 +1,5 @@
+-- Create the `crate_downloads` table.
+
 create table crate_downloads
 (
     crate_id  integer          not null
@@ -13,6 +15,21 @@ comment on table crate_downloads is 'Number of downloads per crate. This was ext
 comment on column crate_downloads.crate_id is 'Reference to the crate that this row belongs to.';
 comment on column crate_downloads.downloads is 'The total number of downloads for this crate.';
 
+-- Create a trigger to automatically add a row to `crate_downloads` when a new
+-- crate is inserted into the `crates` table.
+
+create or replace function insert_crate_downloads_row() returns trigger as $$
+begin
+    insert into crate_downloads(crate_id) values (new.id);
+    return new;
+end;
+$$ language plpgsql;
+
+create trigger insert_crate_downloads_row
+    after insert on crates
+    for each row
+execute function insert_crate_downloads_row();
+
 -- The following query can take a couple of seconds so it should be run manually
 -- outside of the migration to prevent the server from taking a long time to
 -- start up while waiting for the migration to complete.