在视图中动态选择架构名称

Question

I have a view for multiple tables with the same structure but in different schemas:

create table a.persons (
    name text primary key
);
create table b.persons (
    name text primary key
);
create view dynamic_persons as select * from SCHEMA.persons;

I want to be a able to get SCHMEA dynamically from a function or jwt attribute ( current_setting('jwt.claims.schema') for example).
Is it possible to do?

Answer 1

您应该set schema或set search_path to或者select set_config来更改架构，但是视图定义已保存，因此要动态运行它，您将不得不在每次运行时重新创建视图，这没有任何意义。

Answer 2

You can use a table function for that. Create a function, that takes an argument and depending on that argument either queries a.persons or b.persons .

Example:

CREATE TYPE schema_switch AS ENUM ('a', 'b');

CREATE OR REPLACE FUNCTION dynamic_view (_schema schema_switch)
RETURNS TABLE (name text)
AS
$$
DECLARE
  x INT;
BEGIN
  CASE 
    WHEN _schema ='a'
      THEN RETURN QUERY SELECT persons.name
                               FROM a.persons;
    WHEN _schema ='b'
      THEN RETURN QUERY SELECT persons.name
                               FROM b.persons;
  END CASE;
END;
$$
LANGUAGE plpgsql;

Called like dynamic_view('a') would return the records from a.persons , dynamic_view('b') those from b.persons .

In the example I created a new enum type here only allowing 'a' or 'b' for input. That makes it less error prone. But you could of course also do it with a varchar and RAISE an error, if an invalid value was passed. You could also use dynamic SQL to allow passing an arbitrary schema name using RETURN QUERY EXECUTE . But be sure to check the input for sanity then.Like look up pg_catalog.pg_namespace if such a schema exists.

Maybe there is also a possibility doing it with rules instead of a function.