PG_cannot alter type of a column used by a view or rule_解决被视图依赖问题

一、问题背景

PG数据库：需要对一张表修改字段类型的时候，突然报错了（-_-）

从报错信息大致可以看出：是因为这张表的这个字段，被某个视图使用着

二、解决思路

解决思路：

• 备份依赖
• 修改字段类型
• 恢复依赖

---

2.1、备份依赖

2.1.1、创建备份表

--使用前，先初始化对应的方法
 
CREATE TABLE  deps_saved_ddl (
    deps_id serial NOT NULL, -- 依赖ID
    deps_view_schema varchar(255) NULL, -- SCHEMA
    deps_view_name varchar(255) NULL, -- 被依赖的表名
    deps_ddl_to_run text NULL, -- 依赖的DDL
    deps_version varchar(255) NULL, -- 版本
    is_deleted bpchar(1) NULL DEFAULT 0, -- 是否可删除
    CONSTRAINT deps_saved_ddl_pkey PRIMARY KEY (deps_id)
);
COMMENT ON TABLE  deps_saved_ddl IS '用户修改字段时备份依赖';
 
-- Column comments
 
COMMENT ON COLUMN  deps_saved_ddl.deps_id IS '依赖ID';
COMMENT ON COLUMN  deps_saved_ddl.deps_view_schema IS 'SCHEMA';
COMMENT ON COLUMN  deps_saved_ddl.deps_view_name IS '被依赖的表名';
COMMENT ON COLUMN  deps_saved_ddl.deps_ddl_to_run IS '依赖的DDL';
COMMENT ON COLUMN  deps_saved_ddl.deps_version IS '版本';
COMMENT ON COLUMN  deps_saved_ddl.is_deleted IS '是否可删除';
;

2.1.2、创建备份依赖的存储过程

--创建备份依赖的存储过程
create or replace function deps_save_and_drop_dependencies(p_version varchar, p_view_schema varchar, p_view_name varchar) returns void as
$$
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, 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
  
  insert into deps_saved_ddl(deps_version, deps_view_schema, deps_view_name, deps_ddl_to_run)
  select p_version, p_view_schema, p_view_name, 'COMMENT ON ' ||
  case
  when c.relkind = 'v' then 'VIEW'
  when c.relkind = 'm' then 'MATERIALIZED VIEW'
  else ''
  end
  || ' ' || n.nspname || '.' || c.relname || ' IS ''' || replace(d.description, '''', '''''') || ''';'
  from pg_class c
  join pg_namespace n on n.oid = c.relnamespace
  join pg_description d on d.objoid = c.oid and d.objsubid = 0
  where n.nspname = v_curr.obj_schema and c.relname = v_curr.obj_name and d.description is not null;
  
  insert into deps_saved_ddl(deps_version, deps_view_schema, deps_view_name, deps_ddl_to_run)
  select p_version, p_view_schema, p_view_name, 'COMMENT ON COLUMN ' || n.nspname || '.' || c.relname || '.' || a.attname || ' IS ''' || replace(d.description, '''', '''''') || ''';'
  from pg_class c
  join pg_attribute a on c.oid = a.attrelid
  join pg_namespace n on n.oid = c.relnamespace
  join pg_description d on d.objoid = c.oid and d.objsubid = a.attnum
  where n.nspname = v_curr.obj_schema and c.relname = v_curr.obj_name and d.description is not null;
  
  insert into deps_saved_ddl(deps_version, deps_view_schema, deps_view_name, deps_ddl_to_run)
  select p_version, p_view_schema, p_view_name, 'GRANT ' || privilege_type || ' ON ' || table_schema || '.' || table_name || ' TO ' || grantee
  from information_schema.role_table_grants
  where table_schema = v_curr.obj_schema and table_name = v_curr.obj_name;
  
  if v_curr.obj_type = 'v' then
    insert into deps_saved_ddl(deps_version, deps_view_schema, deps_view_name, deps_ddl_to_run)
    select p_version, 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;
  elsif v_curr.obj_type = 'm' then
    insert into deps_saved_ddl(deps_version, deps_view_schema, deps_view_name, deps_ddl_to_run)
    select p_version, p_view_schema, p_view_name, 'CREATE MATERIALIZED VIEW ' || v_curr.obj_schema || '.' || v_curr.obj_name || ' AS ' || definition
    from pg_matviews
    where schemaname = v_curr.obj_schema and matviewname = v_curr.obj_name;
  end if;
  
  execute 'DROP ' ||
  case
    when v_curr.obj_type = 'v' then 'VIEW'
    when v_curr.obj_type = 'm' then 'MATERIALIZED VIEW'
  end
  || ' ' || v_curr.obj_schema || '.' || v_curr.obj_name;
  
end loop;
end;
$$
LANGUAGE plpgsql;

2.2、修改字段的类型

alter table MD_PART_FAMILY alter column PLATEFORM_SCHEME_ID type text using PLATEFORM_SCHEME_ID::text;
alter table MD_PART_FAMILY alter column PLATEFORM_SCHEME type text using PLATEFORM_SCHEME::text;

2.3、恢复依赖

--创建还原依赖的存储过程
create or replace function deps_restore_dependencies(p_version varchar, p_view_schema varchar, p_view_name varchar) returns void as
$$
declare
  v_curr record;
begin
for v_curr in
(
  select deps_ddl_to_run
  from deps_saved_ddl
  where deps_view_schema = p_view_schema and deps_view_name = p_view_name
  and is_deleted = '0'
  order by deps_id desc
) loop
  execute v_curr.deps_ddl_to_run;
end loop;
update deps_saved_ddl set is_deleted = '1'
where deps_view_schema = p_view_schema and deps_view_name = p_view_name and deps_version = p_version;
end;
$$
LANGUAGE plpgsql;

三、日常调用

-- 备份依赖
select deps_save_and_drop_dependencies('2021072200002', 'md', 'md_plateform_scheme');
-- 修改字段类型
alter table md_plateform_scheme alter column pre_plateform_scheme type text using pre_plateform_scheme::text;
-- 恢复依赖
select md.deps_restore_dependencies('2021072200002', 'md', 'md_plateform_scheme');

'1.表名需要小写'
'2.版本号：日期即可'