Suggest using generated columns for Full-Text Search operations

[laurenceisla]

Problem

Complex full-text search cannot be done directly on some cases. For example when using computed fields or if we want to do the FTS to multiple fields at the same time.

Our suggestion in the docs is not correct right now, since it won't use the index created there (#3845 won't fix this since it doesn't include computed fields).

Solution

According to the PostgreSQL docs, there is an option to use generated columns to achieve this:

Another approach is to create a separate tsvector column to hold the output of to_tsvector. To keep this column automatically up to date with its source data, use a stored generated column. This example is a concatenation of title and body, using coalesce to ensure that one field will still be indexed when the other is NULL

So we should suggest using this alternative in the docs.