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Posted by hornedw on 09/01/06 06:14
Jerry Stuckle wrote:
> hornedw wrote:
> > Jerry
> >
> > I was trying to set it up where when a person clicks on books the page
> > would reload and then display Books and then Nonfiction and Fiction
> > would appear under it. Like below
> > Books (35)
> > Electronics(23)
> >
> > The number inside the parenthesis being the number of products in that
> > category. When Books is clicked on, it would display the following
> > Books(35)
> > Fiction(18)
> > Nonfiction(17)
> > Electronics(23)
> >
> > It does not necessaryly have to be spaced over. I may use bulleted list
> > or something like that. The main two things I was trying to do was use
> > the modfied preorder tree algorithm and to have it display the main
> > category and then display the main category and its subcategories and
> > then the rest of the categories on the page. I was debating on whether
> > doing it this way or something similar to the way it is done at
> > Amazon.com on their categories.
> >
> > David
> > Jerry Stuckle wrote:
> >
> >>hornedw wrote:
> >>
> >>>the category table should look like the following. it did not display
> >>>very well in the first message
> >>>
> >>>catid, name,lft,rgt
> >>>1, home,1,1
> >>>2, books,2,17
> >>>4, fiction,3,10
> >>>5, nonfiction, 11,16
> >>>3, electronics,18, 37
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>hornedw wrote:
> >>>
> >>>
> >>>>I have been working on a ecommerce website for myself. What I needed
> >>>>some assistance on was when i was trying to display the
> >>>>categories/subcategories for the different products.
> >>>>I decided to use the modified preorder tree transversal algorithm. What
> >>>>I wanted was on the first page is to display the catogories as follows
> >>>>
> >>>>Books (35)
> >>>>Electronics(23)
> >>>>
> >>>>The number inside the parenthesis being the number of products in that
> >>>>category. When Books is clicked on, it would display the following
> >>>>
> >>>>Books(35)
> >>>> Fiction(18)
> >>>> Nonfiction(17)
> >>>>Electronics(23)
> >>>>
> >>>>In my MYSQL database table, I have the fields catid, name, lft and
> >>>>rgt. For example for the three categories mentioned above I have the
> >>>>following entries
> >>>>
> >>>>catid name lft rgt
> >>>>1 home 1 1
> >>>>2 books 2 17
> >>>>4 fiction 3 10
> >>>>5 nonfiction 11 16
> >>>>3 electronics 18 37
> >>>>
> >>>>
> >>>>The first category home was just used to represent the main root of the
> >>>>whole tree. If anyone could give me some assistance, it would be much
> >>>>appreciated. Thank you in advance.
> >>>
> >>>
> >>I guess I'm confused. How do you link from "fiction" or "nonfiction" to
> >>books?
> >>
> >>This way of doing it looks quite confusing to me.
> >>
> >>
> >>--
> >>==================
> >>Remove the "x" from my email address
> >>Jerry Stuckle
> >>JDS Computer Training Corp.
> >>jstucklex@attglobal.net
> >>==================
> >
> >
>
> Yes, I'm aware of what you're trying to do. What I'm confused about is
> how, from the information you provided, the system is supposed to know
> that fiction and nonfiction fall under books. The example you have
> doesn't show any way to determine if something is a top level category
> or a subcategory - and if the latter, which is its parent category.
>
> P.S. Please don't top post.
>
> --
> ==================
> Remove the "x" from my email address
> Jerry Stuckle
> JDS Computer Training Corp.
> jstucklex@attglobal.net
> ==================
I got most of my information from
http://dev.mysql.com/tech-resources/articles/hierarchical-data.html
Under the section where it says "Nested Set"
I will try to explain using the example I gave.
I noticed on my example that the rgt value for home should have been 38
Here is the datbase values I had in my previous post
catid, name,lft,rgt
> >>>1, home,1,38
> >>>2, books,2,17
> >>>4, fiction,3,10
> >>>5, nonfiction, 11,16
> >>>3, electronics,18, 37
Basically this algorithm sets up the data you are working in as a tree
diagram.Each block has a left and right value. You start on the left of
the root of the tree and go around the diagram and number the blocks. .
If the item has a child, you will number the parent's left value and
the child's left value. If the item is a child, you wll number the left
value and then go to the right value of the child. The difference
between the right and left value of a child is always 1. Once you have
given the child its right value, you will go back up the tree and give
the parent its right value Once you have reached the main parent under
the root, you go to the next main parent that is under the root. You
continue this until you have given the last main parent its right value
and then you give the root its right value.
In the example above, Home has the biggest difference between its right
and left values and therefore is the root. Books is the first main
parent category. The left and right values of fiction and nonfiction
fall between the left and right values of books. That is how books is
the parent category of fiction and nonfiction. Electronics is another
main category in the table. The list I gave above is not a full list
of al the categories and subcategories For example, I do not have any
child subcategories listed. I know this not a very good explanation,
but the website listed above may be of greater help of explaining what
I am trying to do.
David
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