Hi,
I''m trying to understand belongs_to and has_many etc... I understand
the
relationship but I''m trying to figure how this can help me
for example I have two tables
i have 2 tables called mothers and another called childrens
in this childrens model i have this
###Childrens model
belongs_to: mother
..
..
####
now in the
children controller
I want to retrive the mother name currently I''m doing this way
def index ##show all the childrens and their mother''s name
@childrens = Childrens.find(
:all,
:select=>"mothers.name AS mother_name, childrens.* ",
:join=>"LEFT JOIN mothers ON mothers.id = childrens.mother_id"
)
end
I was just curious because of the belongs_to I can skip this left join
on tables
--
Posted via http://www.ruby-forum.com/.
If you have set up the associations (belongs_to and has_many) then if you have a Child object child you can just say child.mother to get the mother. Similarly if you have a mother object you can say mother.children to get the children. It is all done by magic. Colin 2009/5/12 Anthony Ward <rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>> > Hi, > > I''m trying to understand belongs_to and has_many etc... I understand the > relationship but I''m trying to figure how this can help me > > for example I have two tables > i have 2 tables called mothers and another called childrens > in this childrens model i have this > > ###Childrens model > belongs_to: mother > .. > .. > > #### > now in the > children controller > I want to retrive the mother name currently I''m doing this way > > def index ##show all the childrens and their mother''s name > @childrens = Childrens.find( > :all, > :select=>"mothers.name AS mother_name, childrens.* ", > :join=>"LEFT JOIN mothers ON mothers.id = childrens.mother_id" > ) > end > > I was just curious because of the belongs_to I can skip this left join > on tables > -- > Posted via http://www.ruby-forum.com/. > > > >--~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
Hi thanks works like a charm! but i''m just curious performance wise when I look at mongrel it seems that there are two queries first the children.all() then for each record it does a new query for mother get name... now is that as quick compare to juts one query with a left join and get all the data in children(). Colin Law wrote:> If you have set up the associations (belongs_to and has_many) then if > you > have a Child object child you can just say child.mother to get the > mother. > Similarly if you have a mother object you can say mother.children to get > the > children. It is all done by magic. > Colin > > 2009/5/12 Anthony Ward <rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>-- Posted via http://www.ruby-forum.com/.
2009/5/12 Anthony Ward <rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>> > Hi > > thanks works like a charm! > > but i''m just curious performance wise > when I look at mongrel it seems that there are two queries > first the children.all() > then for each record it does a new query for mother get name... > > now is that as quick compare to juts one query with a left join and get > all the data in children(). >If you know you are going to be accessing the associated objects use :include in the find to tell Rails to fetch all the data in one query, so something like @children = Child.find(:all, :include => :mother) By the way, I think the class should be Child, the table children and the controller children_controller. Rails should know that children is the plural of child. If you are really building a database of family relationships then you might want to search for a thread here a few weeks ago about how to organise the db. There were some very interesting ideas discussed. Colin> > > Colin Law wrote: > > If you have set up the associations (belongs_to and has_many) then if > > you > > have a Child object child you can just say child.mother to get the > > mother. > > Similarly if you have a mother object you can say mother.children to get > > the > > children. It is all done by magic. > > Colin > > > > 2009/5/12 Anthony Ward <rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> > > -- > Posted via http://www.ruby-forum.com/. > > > >--~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
Hi thank you so if I use the include how do i just retrieve the name then example this is using the "magic way" @children do |child| ... print child.mother.name end -- Posted via http://www.ruby-forum.com/.
2009/5/12 Anthony Ward <rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>> > Hi thank you > > so if I use the include > how do i just retrieve the name thenDo you mean you want a query finding the child, including the mother.namebut not the other mother fields? I do not know whether you can do that. I think the overhead of fetching all columns is going to be rather small. Colin> > > example this is using the "magic way" > > @children do |child| > > ... print child.mother.name > > end > > > > -- > Posted via http://www.ruby-forum.com/. > > > >--~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
If you want to retrieve just the name, than use the :select option with your find: @children = Child.find(:all, :include => :mother, :select => ''name'') On May 12, 11:04 am, Colin Law <clan...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org> wrote:> 2009/5/12 Anthony Ward <rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> > > > > > Hi thank you > > > so if I use the include > > how do i just retrieve the name then > > Do you mean you want a query finding the child, including the > mother.namebut not the other mother fields? I do not know whether you > can do that. I > think the overhead of fetching all columns is going to be rather small. > Colin > > > > > example this is using the "magic way" > > > @children do |child| > > > ... print child.mother.name > > > end > > > -- > > Posted viahttp://www.ruby-forum.com/.
2009/5/12 pharrington <xenogenesis-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>> > If you want to retrieve just the name, than use the :select option > with your find: > > @children = Child.find(:all, :include => :mother, :select => ''name'') >Does that select child.name or mother.name? Colin> > On May 12, 11:04 am, Colin Law <clan...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org> wrote: > > 2009/5/12 Anthony Ward <rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> > > > > > > > > > Hi thank you > > > > > so if I use the include > > > how do i just retrieve the name then > > > > Do you mean you want a query finding the child, including the > > mother.namebut not the other mother fields? I do not know whether you > > can do that. I > > think the overhead of fetching all columns is going to be rather small. > > Colin > > > > > > > > > example this is using the "magic way" > > > > > @children do |child| > > > > > ... print child.mother.name > > > > > end > > > > > -- > > > Posted viahttp://www.ruby-forum.com/. > > >--~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
Yeah I deleted that post immediately after because that selects child.name. Something like :select => "mothers.name AS mother_name" would probably work, but just ugly AND then you''d need a mother_name virtual attribute in the Child model, making things rather needlessly horrific. I really can''t think of a good way (without raw SQL) to do this in one query either. On May 12, 3:33 pm, Colin Law <clan...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org> wrote:> 2009/5/12 pharrington <xenogene...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> > > > > > If you want to retrieve just the name, than use the :select option > > with your find: > > > @children = Child.find(:all, :include => :mother, :select => ''name'') > > Does that select child.name or mother.name? > Colin > > > > > On May 12, 11:04 am, Colin Law <clan...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org> wrote: > > > 2009/5/12 Anthony Ward <rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> > > > > > Hi thank you > > > > > so if I use the include > > > > how do i just retrieve the name then > > > > Do you mean you want a query finding the child, including the > > > mother.namebut not the other mother fields? I do not know whether you > > > can do that. I > > > think the overhead of fetching all columns is going to be rather small. > > > Colin > > > > > example this is using the "magic way" > > > > > @children do |child| > > > > > ... print child.mother.name > > > > > end > > > > > -- > > > > Posted viahttp://www.ruby-forum.com/.
OK I''m dumb; you definitely don''t need a virtual attribute for that (not really sure what i was thinking), but its still ugly probably not worth doing. On May 12, 4:49 pm, pharrington <xenogene...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:> Yeah I deleted that post immediately after because that selects > child.name. Something like :select => "mothers.name AS mother_name" > would probably work, but just ugly AND then you''d need a mother_name > virtual attribute in the Child model, making things rather needlessly > horrific. I really can''t think of a good way (without raw SQL) to do > this in one query either. > > On May 12, 3:33 pm, Colin Law <clan...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org> wrote: > > > 2009/5/12 pharrington <xenogene...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> > > > > If you want to retrieve just the name, than use the :select option > > > with your find: > > > > @children = Child.find(:all, :include => :mother, :select => ''name'') > > > Does that select child.name or mother.name? > > Colin > > > > On May 12, 11:04 am, Colin Law <clan...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org> wrote: > > > > 2009/5/12 Anthony Ward <rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> > > > > > > Hi thank you > > > > > > so if I use the include > > > > > how do i just retrieve the name then > > > > > Do you mean you want a query finding the child, including the > > > > mother.namebut not the other mother fields? I do not know whether you > > > > can do that. I > > > > think the overhead of fetching all columns is going to be rather small. > > > > Colin > > > > > > example this is using the "magic way" > > > > > > @children do |child| > > > > > > ... print child.mother.name > > > > > > end > > > > > > -- > > > > > Posted viahttp://www.ruby-forum.com/.