Thread: Format generation_expression

Hi,

Currently, I have a problem. I am working on a project with generated columns. I try to implement the generated column feature in the typeorm project. The thing is, I don't want to drop and add a generated column every time the application starts. Therefore I need a way to check whether a generated column expression has changed. 

With select generation_expression from information_schema."columns" c where c.generation_expression is not null; I can retrieve the saved generation expression. However, It seems like Postgres optimizes or changes it. Therefore, it is different.  

Example:

I add a column like this:

alter table company add tsv tsvector generated always as (setweight(to_tsvector('german', coalesce(name, '')), 'A') || setweight(jsonb_to_tsvector('german', keywords::jsonb, '["string"]'),'A')) stored;

Now if I try to retrieve the expression with select c.generation_expression from information_schema."columns" c where c.column_name = 'tsv' and c.table_name = 'company'; it is different. 

Input expression:
setweight(to_tsvector('german', coalesce(title, '')), 'A') || setweight(to_tsvector('german', coalesce(description, '')), 'B');
What I got from postgres:
(setweight(to_tsvector('german'::regconfig, (COALESCE(name, ''::character varying))::text), 'A'::"char") || setweight(jsonb_to_tsvector('german'::regconfig, keywords, '["string"]'::jsonb), 'A'::"char"))

Postgres formats the query in some way. Is there any way to do this manually? 
Like:
magic_function_to_format_sql(`setweight(to_tsvector('german', coalesce(title, '')), 'A') || setweight(to_tsvector('german', coalesce(description, '')), 'B')`) Returns: (setweight(to_tsvector('german'::regconfig, (COALESCE(name, ''::character varying))::text), 'A'::"char") || setweight(jsonb_to_tsvector('german'::regconfig, keywords, '["string"]'::jsonb), 'A'::"char"))

Then I could check if the saved expression is equal to the formatted one. I tried to find information in the documentation. But I had no luck. 

Are you caching the definition some other place in the application stack and checking it later to compare? If so, I would likely alter the table and in the same transaction read the definition as recorded in generation_expression from information_schema.columns. Seems simple enough, but not sure of your overall process.