I'll be using Devart's dotConnect. I have two alternatives at this moment
a) To set the user name to the required schema. This has the (little) drawback that forces user configuration for every schema...
With "ALTER ROLE SET" the user name and initial search_path are both explicitly specified and do not need to match...
b) To manually do something like the JDBC driver you mention, but it triggers some questions b.1) To execute the set search_path one must be connected, database name included. I think by that time, the default schema is determined. Or I am wrong, am I?
You are mistaken. When doing it at the connection-level an actual "SET search_path" SQL command is not generated - instead the server simply uses the data present in the connection string to change runtime variables before the connection is made ready for use.
b.2) The search_path is valid for the database or restricted to the connection?
You need to rephrase this question. From a client's perspective everything is restricted to the connection - and a given connection only exists to a single database at any given time.
And if you can avoid top-posting it would be much appreciated.