Обсуждение: Possible problems with cyclic references
Hi all, me again. I've been looking at the doc's again (must stop doing that!) I've been looking at the 'references' clause to implement referential integrity. My problem is that I'm wanting to create a cyclic reference, and was wondering what problems this may cause, e.g. when restoring from a pg_dump. I have a region table (rregion character(2), rname varchar(40), rliasson int4). I have a teams table (ttid int4, tregion character(2) references region(rregion),...) I have a members table (mid int4, mteam references teams(tid),.........) Pretty straight forward so far, a member must be a part of a team and a team must be in a region. My problem is that I want to set rliasson as a reference to members (mid) as the Regional Liasson Officer for each region is a member. -- Gary Stainburn This email does not contain private or confidential material as it may be snooped on by interested government parties for unknown and undisclosed purposes - Regulation of Investigatory Powers Act, 2000
Gary Stainburn wrote: > Hi all, me again. > > I've been looking at the doc's again (must stop doing that!) > > I've been looking at the 'references' clause to implement referential > integrity. My problem is that I'm wanting to create a cyclic reference, and > was wondering what problems this may cause, e.g. when restoring from a > pg_dump. > > I have a region table (rregion character(2), rname varchar(40), rliasson > int4). > I have a teams table (ttid int4, tregion character(2) references > region(rregion),...) > I have a members table (mid int4, mteam references teams(tid),.........) > > Pretty straight forward so far, a member must be a part of a team and a team > must be in a region. My problem is that I want to set rliasson as a > reference to members (mid) as the Regional Liasson Officer for each region is > a member. No problem. pg_dump outputs commands to disable referential integrity checks during the restore. And you could even make rliasson NOT NULL. All you have to do then is to have the constraints INITIALLY DEFERRED andinsert all the cyclic rows in one transaction. Add the constraint to the region table with ALTER TABLE after creating the members table. Jan -- #======================================================================# # It's easier to get forgiveness for being wrong than for being right. # # Let's break this rule - forgive me. # #================================================== JanWieck@Yahoo.com # _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com
Hi Jan, Thanks for the additional info. I did, having already posted the msg, tru to create the references, but found that it would not let me do that as I was trying to create a reference to a table that didn't exist yet. I ended up setting up a one-way reference, running pg_dump to see how to set up the reference after creating the tables (it uses create triggers), and then changing/adding these lines to my create script. Your way seems much nicer. Gary On Monday 23 July 2001 3:18 pm, Jan Wieck wrote: > Gary Stainburn wrote: > > Hi all, me again. > > > > I've been looking at the doc's again (must stop doing that!) > > > > I've been looking at the 'references' clause to implement referential > > integrity. My problem is that I'm wanting to create a cyclic reference, > > and was wondering what problems this may cause, e.g. when restoring from > > a pg_dump. > > > > I have a region table (rregion character(2), rname varchar(40), rliasson > > int4). > > I have a teams table (ttid int4, tregion character(2) references > > region(rregion),...) > > I have a members table (mid int4, mteam references teams(tid),.........) > > > > Pretty straight forward so far, a member must be a part of a team and a > > team must be in a region. My problem is that I want to set rliasson as a > > reference to members (mid) as the Regional Liasson Officer for each > > region is a member. > > No problem. pg_dump outputs commands to disable referential > integrity checks during the restore. > > And you could even make rliasson NOT NULL. All you have to do > then is to have the constraints INITIALLY DEFERRED and insert > all the cyclic rows in one transaction. > > Add the constraint to the region table with ALTER TABLE after > creating the members table. > > > Jan > > -- > > #======================================================================# > # It's easier to get forgiveness for being wrong than for being right. # > # Let's break this rule - forgive me. # > #================================================== JanWieck@Yahoo.com # > > > > _________________________________________________________ > Do You Yahoo!? > Get your free @yahoo.com address at http://mail.yahoo.com -- Gary Stainburn This email does not contain private or confidential material as it may be snooped on by interested government parties for unknown and undisclosed purposes - Regulation of Investigatory Powers Act, 2000