Merge branch 'add-view-helper-functions' of https://github.com/eiknat/lemmy into...

diff --combined migrations/2020-09-07-231141_add_migration_utils/down.sql
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--- /dev/null
--- 2/server/migrations/2020-09-07-231141_add_migration_utils/down.sql
+++ b/migrations/2020-09-07-231141_add_migration_utils/down.sql
@@@ -1,0 -1,1 +1,1 @@@
+ drop schema utils cascade;

diff --combined migrations/2020-09-07-231141_add_migration_utils/up.sql
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--- /dev/null
--- 2/server/migrations/2020-09-07-231141_add_migration_utils/up.sql
+++ b/migrations/2020-09-07-231141_add_migration_utils/up.sql
@@@ -1,0 -1,89 +1,89 @@@
+ create schema utils;
+ 
+ create table utils.deps_saved_ddl
+ (
+   id serial NOT NULL,
+   view_schema character varying(255),
+   view_name character varying(255),
+   ddl_to_run text,
+   CONSTRAINT deps_saved_ddl_pkey PRIMARY KEY (id)
+ );
+ 
+ create or replace function utils.save_and_drop_views(p_view_schema name, p_view_name name)
+     RETURNS void
+     LANGUAGE plpgsql
+     COST 100
+ AS $BODY$
+ 
+ declare
+   v_curr record;
+ begin
+ for v_curr in 
+ (
+   select obj_schema, obj_name, obj_type from
+   (
+   with recursive recursive_deps(obj_schema, obj_name, obj_type, depth) as 
+   (
+     select p_view_schema::name, p_view_name, null::varchar, 0
+     union
+     select dep_schema::varchar, dep_name::varchar, dep_type::varchar, recursive_deps.depth + 1 from 
+     (
+       select ref_nsp.nspname ref_schema, ref_cl.relname ref_name, 
+       rwr_cl.relkind dep_type,
+       rwr_nsp.nspname dep_schema,
+       rwr_cl.relname dep_name
+       from pg_depend dep
+       join pg_class ref_cl on dep.refobjid = ref_cl.oid
+       join pg_namespace ref_nsp on ref_cl.relnamespace = ref_nsp.oid
+       join pg_rewrite rwr on dep.objid = rwr.oid
+       join pg_class rwr_cl on rwr.ev_class = rwr_cl.oid
+       join pg_namespace rwr_nsp on rwr_cl.relnamespace = rwr_nsp.oid
+       where dep.deptype = 'n'
+       and dep.classid = 'pg_rewrite'::regclass
+     ) deps
+     join recursive_deps on deps.ref_schema = recursive_deps.obj_schema and deps.ref_name = recursive_deps.obj_name
+     where (deps.ref_schema != deps.dep_schema or deps.ref_name != deps.dep_name)
+   )
+   select obj_schema, obj_name, obj_type, depth
+   from recursive_deps 
+   where depth > 0
+   ) t
+   group by obj_schema, obj_name, obj_type
+   order by max(depth) desc
+ ) loop
+   if v_curr.obj_type = 'v' then
+     insert into utils.deps_saved_ddl(view_schema, view_name, ddl_to_run)
+     select p_view_schema, p_view_name, 'CREATE VIEW ' || v_curr.obj_schema || '.' || v_curr.obj_name || ' AS ' || view_definition
+     from information_schema.views
+     where table_schema = v_curr.obj_schema and table_name = v_curr.obj_name;
+ 
+     execute 'DROP VIEW' || ' ' || v_curr.obj_schema || '.' || v_curr.obj_name;
+   end if;
+ end loop;
+ end;
+ $BODY$;
+ 
+ create or replace function utils.restore_views(p_view_schema character varying, p_view_name character varying)
+   RETURNS void 
+   LANGUAGE plpgsql
+   COST 100
+ AS $BODY$
+ declare
+   v_curr record;
+ begin
+ for v_curr in 
+ (
+   select ddl_to_run, id 
+   from utils.deps_saved_ddl
+   where view_schema = p_view_schema and view_name = p_view_name
+   order by id desc
+ ) loop
+ begin
+   execute v_curr.ddl_to_run;
+   delete from utils.deps_saved_ddl where id = v_curr.id;
+   EXCEPTION WHEN OTHERS THEN
+       -- keep looping, but please check for errors or remove left overs to handle manually
+         end;
+ end loop;
+ end;
+ $BODY$;