module ActiveRecord::ConnectionAdapters::PostgreSQL::SchemaStatements

def schema_search_path=(schema_csv)

This should be not be called manually but set in database.yml.

See: https://www.postgresql.org/docs/current/static/ddl-schemas.html
Names beginning with $ have to be quoted (e.g. $user => '$user').
Sets the schema search path to a string of comma-separated schema names. 
def schema_search_path=(schema_csv)
  if schema_csv
    execute("SET search_path TO #{schema_csv}", "SCHEMA")
    @schema_search_path = schema_csv
  end
end