# Two questions about data structures

**URL:** <https://www.ruby-forum.com/t/two-questions-about-data-structures/62662>\
**Category:** Ruby\
**Created:** [June 7, 2006, 3:13am UTC](https://www.ruby-forum.com/t/two-questions-about-data-structures/62662 "2006-06-07T03:13:55Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![Tim\_U](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/90db22/32.png) [@Tim\_U](https://www.ruby-forum.com/u/Tim_U)\
**Post date:** [June 7, 2006, 3:13am UTC](https://www.ruby-forum.com/t/two-questions-about-data-structures/62662/1 "2006-06-07T03:13:55Z")

</div>

I am building an application and would like the groups advice on the  
following two scenarios.

1. I have a table about an entity and there are a LOT of options about  
this entitiy. For example isLeftHanded? isRedHaired? doesLikeRedRoses?  
doesHatePolenta? etc. What is the best way to keep these kinds of  
binary information about an entity? Is there any harm in just adding  
binary fields? Should I use a large number field and OR all the time  
(does limit the number of options per field and makes for messy SQL  
though). Should I have a text field with delimited data in it? Should  
I join a separate table?

2. related to above: I need to keep other types of prefs that don’t  
apply to all entitities of a type. For example:  
preferedInvoiceFormat, clientURL etc. The tricky thing is that it  
would be nice to have some defaults so that if a preference was not  
specified for a client then a global one could be used. It gets even  
more tricky when you have something like this. product, location,  
package, client, price. The idea is that a product will cost  
different amounts depending on who is ordering it, where and as a part  
of which package. Again there should be a way to specify defaults  
like so widget, \*, \*, _,10.00 or ,alabama,,_,20.00. I the first  
example unless otherwise specified all widgets cost 10 dollars. In the  
second example unless otherwise specified all products in alabama cost  
20 dollars.

Has anybody dealt with data like this and if so how.

---

<div class="post-metadata">

**Author:** ![Tim\_U](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/90db22/32.png) [@Tim\_U](https://www.ruby-forum.com/u/Tim_U)\
**Post date:** [June 7, 2006, 11:06am UTC](https://www.ruby-forum.com/t/two-questions-about-data-structures/62662/2 "2006-06-07T11:06:30Z")

</div>

Tim U. wrote:

> I have a table about an entity and there are a LOT of options about  
> this entitiy. For example isLeftHanded? isRedHaired? doesLikeRedRoses?  
> doesHatePolenta? etc. What is the best way to keep these kinds of  
> binary information about an entity? Is there any harm in just adding  
> binary fields? Should I use a large number field and OR all the time  
> (does limit the number of options per field and makes for messy SQL  
> though). Should I have a text field with delimited data in it? Should  
> I join a separate table?

Do you want a class to represent such an entity?

class Entity  
def initialize  
@opts = {:left\_handed =\> false, :red\_haired =\> true}  
end

```
 def method_missing(name, *args)
   key = name.to_s[0..-2].to_sym
   case name.to_s
   when /\?$/
     @opts[key]
   when /=$/
     @opts[key] = args.first
   when /!$/
     @opts[key] = !@opts[key]
   else
     super
   end
 end

```

end

entity = Entity.new  
entity.red\_haired? =\> true  
entity.red\_haired!  
entity.red\_haired? =\> false  
entity.left\_handed? =\> false  
entity.left\_handed = true  
entity.left\_handed? =\> true

Furthermore, you could make the class smarter by allowing the options to  
be symbols that reference other options, i.e.

# `right\_handed’ will be the opposite of

# `left\_handed’.

entity.right\_handed = :left\_handed!

entity.female = :male!

# `hippie’ will have the same value

# as `long\_haired’

entity.hippie = :long\_haired

And perhaps even allow procs:

entity.hippie = proc{|opts| opts[:long\_haired] and  
opts[:likes\_hendrix]}

You could use #respond\_to? to determine the type of the value.

Cheers,  
Daniel

---

<div class="post-metadata">

**Author:** ![Tim\_U](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/90db22/32.png) [@Tim\_U](https://www.ruby-forum.com/u/Tim_U)\
**Post date:** [June 7, 2006, 11:54am UTC](https://www.ruby-forum.com/t/two-questions-about-data-structures/62662/3 "2006-06-07T11:54:13Z")

</div>

I’m such a nice guy…

class Entity  
def initialize  
@opts = {:left\_handed =\> false, :red\_haired =\> true}  
end

```
 def method_missing(name, *args)
   key = name.to_s[0..-2].to_sym
   case name.to_s
   when /\?$/
     value = @opts[key]
     if value.respond_to? :to_sym
       if value.to_s =~ /!$/
         !@opts[value.to_s[0..-2].to_sym]
       else
         @opts[value.to_sym]
       end
     elsif value.respond_to? :to_proc
       instance_eval(&value)
     else
       value
     end
   when /=$/
     @opts[key] = args.first
   when /!$/
     @opts[key] = !@opts[key]
   else
     super
   end
 end

```

end

entity = Entity.new  
entity.likes\_hendrix = true  
entity.long\_haired = true  
entity.hippie = proc{long\_haired? and likes\_hendrix?}  
entity.hippie? =\> true

Cheers,  
Daniel

---

<div class="post-metadata">

**Author:** ![Tim\_U](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/90db22/32.png) [@Tim\_U](https://www.ruby-forum.com/u/Tim_U)\
**Post date:** [June 8, 2006, 1:31pm UTC](https://www.ruby-forum.com/t/two-questions-about-data-structures/62662/4 "2006-06-08T13:31:09Z")

</div>

I understand what you are doing I think. It’s a neat solution. But how  
do I store that stuff in a database?

---

<div class="post-metadata">

**Author:** ![Tim\_U](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/90db22/32.png) [@Tim\_U](https://www.ruby-forum.com/u/Tim_U)\
**Post date:** [June 7, 2006, 11:54am UTC](https://www.ruby-forum.com/t/two-questions-about-data-structures/62662/5 "2006-06-07T11:54:50Z")

</div>

I was thinking more about how to save all those options in the  
database and still be able to manipulate them via activerecord. One  
thing I could do of course is to stream the options to yaml and store  
that but that strikes as me as beeing a bit too rubyish. What I mean  
is that if the data is to be used by something else (say a report  
engine) then it won’t do any good to store it in a yaml blob.

Another thing I though of was to use some database specific XML  
thingie. I know postgres can store XML and query it with xpath but  
again that strikes me as beeing a bit too specific.

---

<div class="post-metadata">

**Author:** ![Tim\_U](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/90db22/32.png) [@Tim\_U](https://www.ruby-forum.com/u/Tim_U)\
**Post date:** [June 8, 2006, 1:56pm UTC](https://www.ruby-forum.com/t/two-questions-about-data-structures/62662/6 "2006-06-08T13:56:03Z")

</div>

Tim U. wrote:

> I understand what you are doing I think. It’s a neat solution. But how  
> do I store that stuff in a database?

@opts contains the keys and the boolean values (if you go for the  
extended version, you may have to go through the values and turn the  
symbols and procs into booleans.) I’m not sure what kind of database  
structure you have, but those could be used as name-value pairs of some  
sort. That’s how I’d do it.

Cheers,  
Daniel