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Student

2007-Sep-17 23:37 UTC

DISTINCT?

This should be easy, but I''m stumped...

class X < ActiveRecord::Base
  belongs_to :y
end
class Y < ActiveRecord::Base
  has_many :x
end

The y table has a column names.  The x table has a column value.  I
want the list of values in x for the name "Location" in y.  Yes, there
are many repetitions.

I can probably hack together an SQL statement to do this without too
much trouble, but the point of using rails is kinda to avoid that when
we can, right?

Student


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Conrad Taylor

2007-Sep-18 00:15 UTC

head link

Re: DISTINCT?

Hi, if you would like to obtain the x collection of y, you simply need to do
the following:

renaming y to teacher

renaming x to student

Now, we can say the following:

a_teacher.students

Good luck,

-Conrad

On 9/17/07, Student
<blogger-gRoFi9f2ETe4oY6Ej3vMAKxOck334EZe@public.gmane.org>
wrote:>
>
> This should be easy, but I''m stumped...
>
> class X < ActiveRecord::Base
>   belongs_to :y
> end
> class Y < ActiveRecord::Base
>   has_many :x
> end
>
> The y table has a column names.  The x table has a column value.  I
> want the list of values in x for the name "Location" in y.  Yes,
there
> are many repetitions.
>
> I can probably hack together an SQL statement to do this without too
> much trouble, but the point of using rails is kinda to avoid that when
> we can, right?
>
> Student
>
>
> >
>
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Student

2007-Sep-18 03:14 UTC

head link

Re: DISTINCT?

No, I''m looking for the names of the teachers who teach fifth grade.

On Sep 17, 7:15 pm, "Conrad Taylor"
<conra...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> Hi, if you would like to obtain the x collection of y, you simply need to
do
> the following:
>
> renaming y to teacher
>
> renaming x to student
>
> Now, we can say the following:
>
> a_teacher.students
>
> Good luck,
>
> -Conrad
>
> On 9/17/07, Student
<blog...-gRoFi9f2ETe4oY6Ej3vMAKxOck334EZe@public.gmane.org> wrote:
>
>
>
> > This should be easy, but I''m stumped...
>
> > class X < ActiveRecord::Base
> >   belongs_to :y
> > end
> > class Y < ActiveRecord::Base
> >   has_many :x
> > end
>
> > The y table has a column names.  The x table has a column value.  I
> > want the list of values in x for the name "Location" in y. 
Yes, there
> > are many repetitions.
>
> > I can probably hack together an SQL statement to do this without too
> > much trouble, but the point of using rails is kinda to avoid that when
> > we can, right?
>
> > Student

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Student

2007-Sep-18 03:20 UTC

head link

Re: DISTINCT?

No, I''m looking for the names of all of the teachers who are teaching
students that are in the fifth grade.  (The students are in the fifth
grade.)

On Sep 17, 7:15 pm, "Conrad Taylor"
<conra...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> Hi, if you would like to obtain the x collection of y, you simply need to
do
> the following:
>
> renaming y to teacher
>
> renaming x to student
>
> Now, we can say the following:
>
> a_teacher.students
>
> Good luck,
>
> -Conrad
>
> On 9/17/07, Student
<blog...-gRoFi9f2ETe4oY6Ej3vMAKxOck334EZe@public.gmane.org> wrote:
>
>
>
> > This should be easy, but I''m stumped...
>
> > class X < ActiveRecord::Base
> >   belongs_to :y
> > end
> > class Y < ActiveRecord::Base
> >   has_many :x
> > end
>
> > The y table has a column names.  The x table has a column value.  I
> > want the list of values in x for the name "Location" in y. 
Yes, there
> > are many repetitions.
>
> > I can probably hack together an SQL statement to do this without too
> > much trouble, but the point of using rails is kinda to avoid that when
> > we can, right?
>
> > Student

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Student

2007-Sep-18 12:37 UTC

head link

Re: DISTINCT?

No, I''m looking for the first names of the students of the band
teachers.

On Sep 17, 7:15 pm, "Conrad Taylor"
<conra...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> Hi, if you would like to obtain the x collection of y, you simply need to
do
> the following:
>
> renaming y to teacher
>
> renaming x to student
>
> Now, we can say the following:
>
> a_teacher.students
>
> Good luck,
>
> -Conrad
>
> On 9/17/07, Student
<blog...-gRoFi9f2ETe4oY6Ej3vMAKxOck334EZe@public.gmane.org> wrote:
>
>
>
> > This should be easy, but I''m stumped...
>
> > class X < ActiveRecord::Base
> >   belongs_to :y
> > end
> > class Y < ActiveRecord::Base
> >   has_many :x
> > end
>
> > The y table has a column names.  The x table has a column value.  I
> > want the list of values in x for the name "Location" in y. 
Yes, there
> > are many repetitions.
>
> > I can probably hack together an SQL statement to do this without too
> > much trouble, but the point of using rails is kinda to avoid that when
> > we can, right?
>
> > Student

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Bob Showalter

2007-Sep-18 12:59 UTC

head link

Re: DISTINCT?

On 9/17/07, Student
<blogger-gRoFi9f2ETe4oY6Ej3vMAKxOck334EZe@public.gmane.org>
wrote:>
> This should be easy, but I''m stumped...
>
> class X < ActiveRecord::Base
>   belongs_to :y
> end
> class Y < ActiveRecord::Base
>   has_many :x
> end
>
> The y table has a column names.  The x table has a column value.  I
> want the list of values in x for the name "Location" in y.  Yes,
there
> are many repetitions.
You first find the Y row for "Location":

   row = Y.find_by_names(''Location'')

That returns nil if there is no such row. If there are multiple rows,
it returns only the first. If you want all matches, you need to use

   rows = Y.find_all_by_names(''Location'')

Then all the associated X rows can be found via the "x" method of the
Y object:

   results = row.x.collect :&value

(n.b. the normal convention is to use the plural form in has_many;
i.e. "has_many :xs")

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Bob Showalter

2007-Sep-18 13:06 UTC

head link

Re: DISTINCT?

On 9/18/07, Student
<blogger-gRoFi9f2ETe4oY6Ej3vMAKxOck334EZe@public.gmane.org>
wrote:>
> No, I''m looking for the first names of the students of the band
> teachers.
That doesn''t match your original description of the problem.

Why not give us the actual models, columns, etc. It''s hard to think in
terms of x''s and y''s.

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Student

2007-Sep-18 13:17 UTC

head link

Re: DISTINCT?

So I see.  </blush>

class Subprojectattr < ActiveRecord::Base
  belongs_to :attribute
end
class Attribute < ActiveRecord::Base
  has_many :subprojectattrs
end

So I want the list of Subprojectattr.valueStrs when spa.attribute.name
== "Location".  Yes, this is a legacy database, so I cannot fix the
organizational problems via schema changes.

Student


On Sep 18, 8:06 am, "Bob Showalter"
<showa...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> On 9/18/07, Student
<blog...-gRoFi9f2ETe4oY6Ej3vMAKxOck334EZe@public.gmane.org> wrote:
>
>
>
> > No, I''m looking for the first names of the students of the
band
> > teachers.
>
> That doesn''t match your original description of the problem.
>
> Why not give us the actual models, columns, etc. It''s hard to
think in
> terms of x''s and y''s.

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Student

2007-Sep-18 13:31 UTC

head link

Re: DISTINCT?

BTW, I get the results I want with the following sql:

SELECT     dbo.subProjectAttr.valueStr
FROM         dbo.subProjectAttr INNER JOIN
                      dbo.attribute ON dbo.subProjectAttr.attributeId
= dbo.attribute.attributeId
WHERE     (dbo.attribute.name = ''Location'')
GROUP BY dbo.subProjectAttr.valueStr

As I said, however, the idea is to avoid having to put this stuff in
directly.

On Sep 18, 8:17 am, Student
<blog...-gRoFi9f2ETe4oY6Ej3vMAKxOck334EZe@public.gmane.org>
wrote:> So I see.  </blush>
>
> class Subprojectattr < ActiveRecord::Base
>   belongs_to :attribute
> end
> class Attribute < ActiveRecord::Base
>   has_many :subprojectattrs
> end
>
> So I want the list of Subprojectattr.valueStrs when spa.attribute.name
> == "Location".  Yes, this is a legacy database, so I cannot fix
the
> organizational problems via schema changes.
>
> Student
>
> On Sep 18, 8:06 am, "Bob Showalter"
<showa...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > On 9/18/07, Student
<blog...-gRoFi9f2ETe4oY6Ej3vMAKxOck334EZe@public.gmane.org> wrote:
>
> > > No, I''m looking for the first names of the students of
the band
> > > teachers.
>
> > That doesn''t match your original description of the problem.
>
> > Why not give us the actual models, columns, etc. It''s hard to
think in
> > terms of x''s and y''s.

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