问题
This should be SO simple. I want to retrieve the nextval of a sequence... it's not a default value... it's not a primary key... it's not a foreign key. In rare cases, I need a sequence number for a user supplied value.
I've tried the following:
@nextid = ActiveRecord::Base.connection.execute("SELECT nextval('xscrpt_id_seq')")
and what I get back is:
#<PG::Result:0x007fe668a854e8 @connection=#<PG::Connection:0x00000003aeff30>>
And by using
@nextid[0]["nextval"]
I can get the correct value, but it doesn't seem like the right way to approach the problem. I've searched, I read "Pro Active Record", which said to use:
M_script.find_by_sql("SELECT nextval('xscript_id_seq')")
but, that didn't work.
Any hints on the "correct" (Rails way) to retrieve a nextval from a sequence in ROR, would be very appreciated!
回答1:
I believe
ActiveRecord::Base.connection.execute("SELECT nextval('xscrpt_id_seq')")
is the correct solution. As I said in my original question, I checked the book "Pro Active Record" and it is their recommended solution. I'm still not exactly sure how ActiveRecord is making the connection, or if there's any maintenance I need to do (such as closing it).
ActiveRecord used to have a "next_sequence_number" method, but that has been deprecated.
回答2:
You probably want to use select_value and sequence_name:
Xscrpt.connection.select_value("select nextval('#{Xscrpt.sequence_name}')").to_i
回答3:
This works too:
@seq = Smodelname.find_by_sql(" select seq_name.nextval as id from dual ")[0][:id]
来源：https://stackoverflow.com/questions/17954524/retrieve-the-nextval-from-a-sequence-using-activerecord-in-ruby-on-rails-3-2-14