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

migrations/2020-09-07-231141_add_migration_utils/down.sql

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+drop schema utils cascade;

migrations/2020-09-07-231141_add_migration_utils/up.sql

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+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;
+$BODY$;