Comments on: Rails has and belongs to many (habtm) demystified

By: has_and_belongs_to_many relationship not associating both ways - Programmers Goodies

Sun, 21 Aug 2011 14:52:48 +0000

[...] Is the has_and_belongs_to_many present in both models? It sounds like it is not, whereas it should be: [...]

By: marc_andre

marc_andre — Thu, 03 Mar 2011 21:38:06 +0000

Nice post. I noticed you didn't label the checkboxes for the OS, you may want to edit your post to make the UI more user-friendly. See also http://giraffesoft.ca/blog/200...

By: Learning Ruby – Drop Down Lists in One to Many Relationships « Tunaslut

Wed, 12 May 2010 18:47:06 +0000

[...] here for some good reading on relationships in [...]

By: mike

mike — Wed, 10 Mar 2010 02:20:33 +0000

Thank you very much for your effort in putting this info up. I have a love/hate relationship with rails, and I do the exact same thing every time I do habtm in rails. I have bookmarked this page for future reference…thanks again! (deciphering rails' convention with habtm when you have ModelThing and ModelStuff. where do the underscores go and what/where gets pluralized? NARGH!)

By: Michael

Michael — Fri, 27 Mar 2009 20:00:23 +0000

@Clint: I am no expert, either. I have never used the "rescue []" myself, so I'll have to crack open and irb session and explore some more on this one. Thanks for the tip! as for the check for an item existing in a list, I hear that detect is faster than include, but I have not verified. An example:

<%= check_box_tag("browser[os_list][#{os.id}]", "1", 
             @browser.oses.detect{|d| d == os}) %>

You probably know this, but one thing to watch out for when assigning new associations is to remember that the user can opt to remove existing assocations, so that's why I do the delete all. I used to write a lot of code to detect and add/remove but found the code getting far more complicated than if I just simply cleared the list and add the chosen associations afresh.

By: Clint

Clint — Thu, 26 Mar 2009 17:52:52 +0000

I’m not an expert, but wouldn’t this do the same thing?

def update_oses
oses.delete_all
self.oses << Os.find(os_list.keys) rescue []
end

I often do this to add new associates to users for instance but have wondered if it was the most efficient.

user.browsers << browser unless user.browsers.include?(browser)