Ruby Data Structure Query Abstractions/Patterns

[Nicholas Van Weerdenburg]

Hi all,

I've written a small ruby application that uses YAML and the
associated hash/array Ruby structure.

I am now looking to do some query-like actions on the basic ruby data
structure. I'm wondering if there are any packages of
query-abstractions that make sense for Ruby in a generalized sort-of
way. E.g. XPath and XQuery for XML, SQL for RDMS, etc.

Currently I've written my structure-parsing code with a few of my
cases, and I'm starting to refactor with blocks and lambdas in order
to keep duplication low and offer an easily configurable higher-level
of abstraction. Now the code is starting to pressure me to create a
simple query language. Maybe I should go to a ruby db or sqlite, but I
expect I ultimately only need the most basic functionality.

Any suggestions or recommendations?

Thanks,
Nick

 

[PA]

Any suggestions or recommendations?

Not quite sure how well this would fit with Ruby, but you may want to
take a look at SODA [1] which could be used to query generic object
graphs.

In addition, you may want to consider EOQualifier for, er,
"inspiration":

http://developer.apple.com/documentation/WebObjects/Reference/API/com/
webobjects/eocontrol/EOQualifier.html

Cheers,

PA.

[1] http://sodaquery.sourceforge.net/

 

[Robert Klemme]

Hi all,

I've written a small ruby application that uses YAML and the
associated hash/array Ruby structure.

I am now looking to do some query-like actions on the basic ruby data
structure. I'm wondering if there are any packages of
query-abstractions that make sense for Ruby in a generalized sort-of
way. E.g. XPath and XQuery for XML, SQL for RDMS, etc.

Currently I've written my structure-parsing code with a few of my
cases, and I'm starting to refactor with blocks and lambdas in order
to keep duplication low and offer an easily configurable higher-level
of abstraction. Now the code is starting to pressure me to create a
simple query language. Maybe I should go to a ruby db or sqlite, but I
expect I ultimately only need the most basic functionality.

Any suggestions or recommendations?

Another thought: maybe you can even use Ruby itself. I mean, one can
produce quite readable select expressions in Ruby and we have
Enumerable#all?, #any? etc. You might want to add some functionality for
recursive traversal though.

Kind regards

robert

 

[Sam Roberts]

Quoteing (e-mail address removed), on Thu, Jan 06, 2005 at 03:26:22AM +0900:

Hi all,

I've written a small ruby application that uses YAML and the
associated hash/array Ruby structure.

I am now looking to do some query-like actions on the basic ruby data
structure. I'm wondering if there are any packages of
query-abstractions that make sense for Ruby in a generalized sort-of
way. E.g. XPath and XQuery for XML, SQL for RDMS, etc.

This is why you might want to consider XML... then you can just USE
XPath.

Sam

 

[Nicholas Van Weerdenburg]

Thanks. Both links are very interesting.

Regards,
Nick

Any suggestions or recommendations?

Not quite sure how well this would fit with Ruby, but you may want to
take a look at SODA [1] which could be used to query generic object
graphs.

In addition, you may want to consider EOQualifier for, er,
"inspiration":

http://developer.apple.com/documentation/WebObjects/Reference/API/com/
webobjects/eocontrol/EOQualifier.html

Cheers,

PA.

[1] http://sodaquery.sourceforge.net/

 

[Nicholas Van Weerdenburg]

Another thought: maybe you can even use Ruby itself. I mean, one can
produce quite readable select expressions in Ruby and we have
Enumerable#all?, #any? etc. You might want to add some functionality for
recursive traversal though.

Kind regards

robert

I like the idea of using Ruby, and have been extending my code in that
manner. However, XML becomes interesting soon because of it's DOM
traversal capabilities.

I'm also wondering if I'm missing some common Ruby/Perl/Python idiom
for handling in-memory data-structure traversal in a more abstract
way, but so far it doesn't look like it.

Does it make sense to have a general data-structure traversal/query
api in a language like Ruby?

Thanks,
Nick

 

[Nicholas Van Weerdenburg]

Quoteing (e-mail address removed), on Thu, Jan 06, 2005 at 03:26:22AM +0900:


This is why you might want to consider XML... then you can just USE
XPath.

Sam

This is looking like the most reasonable choice at the moment- though
not the most fun, so I may continue with a Ruby solution for now.

Thanks,
Nick

 

[Sam Roberts]

Quoteing (e-mail address removed), on Thu, Jan 06, 2005 at 01:20:40PM +0900:

This is looking like the most reasonable choice at the moment- though
not the most fun, so I may continue with a Ruby solution for now.

I don't know, what's not fun about XML?

Rant: for years the world fills up with adhoc 1/2 solutions to data
structuring, then people decide that reinventing the wheel is dumb, and
make XML, and start adding tons of useful tools to it, like query
languages. The folks come along and say 'its too big and complicated"
and start again... There will soon be a YPath (YAML query language),
mark my words!

Ok, I feel better.

That aside, it sounds kind of cool making a rubyish query language for
ruby data structures... maybe XPath from Rexml could actually be abused
for your purpose, or used to implement a similar language?

Have fun!
Sam

 

[gabriele renzi]

PA ha scritto:

Any suggestions or recommendations?

Not quite sure how well this would fit with Ruby, but you may want to
take a look at SODA [1] which could be used to query generic object
graphs.

In addition, you may want to consider EOQualifier for, er, "inspiration":

http://developer.apple.com/documentation/WebObjects/Reference/API/com/
webobjects/eocontrol/EOQualifier.html

Cheers,

PA.

[1] http://sodaquery.sourceforge.net/

also, JXPath allows XPAth to be applied to generic graphs, maybe of interest

 

[Robert Klemme]

I like the idea of using Ruby, and have been extending my code in that
manner. However, XML becomes interesting soon because of it's DOM
traversal capabilities.

I'm also wondering if I'm missing some common Ruby/Perl/Python idiom
for handling in-memory data-structure traversal in a more abstract
way, but so far it doesn't look like it.

Does it make sense to have a general data-structure traversal/query
api in a language like Ruby?

I'd say yes, but maybe only for certain types (DOM tree nodes) - not
necessarily for general Hash, Array and the like. OTOH you can cook up
something quite easily though:

class Object
def traverse() yield self end
end

module Enumerable
def traverse(&b)
each {|o| o.traverse(&b)}
end
end

class Hash
def traverse(&b)
each {|k,v| v.traverse(&b)}
end
end

Note that this does not take care of looks in the object graph. To do that,
you need to do a bit more:

class Object
def traverse(context = {}) context[self.id] ||= (yield self; true) end
end

module Enumerable
def traverse(context = {}, &b)
unless context[self.id]
context[self.id] = true
each {|o| o.traverse(context, &b)}
end
end
end

class Hash
def traverse(context = {}, &b)
unless context[self.id]
context[self.id] = true
each {|k,v| v.traverse(context, &b)}
end
end
end

Kind regards

robert

 

[Sam Roberts]

Quoteing (e-mail address removed), on Thu, Jan 06, 2005 at 02:46:30PM +0900:

Since you did not include any smileys ...

(1) Having a uniform and extensible concrete syntax for tree structures is
great
(2) Having a whole set of uniform manipulations on (1) is great
(3) Insisting on applying (1) to the concrete syntax of (2) is absurd and
the result, ugly

I don't know what (3) is talking about. The syntax of XPath isn't XML.
It's a domain-specific language inside XML, much as regexs are a
domain-specific language inside ruby.

Just about every (computer) language has a natural underlying tree
structure, with lots of cross-tree links. So, should we now start to write
our Ruby using XML ?

No, nor YAML, has anybody suggested doing so?

Sam

 

[Nicholas Van Weerdenburg]

I like the idea of using Ruby, and have been extending my code in that
manner. However, XML becomes interesting soon because of it's DOM
traversal capabilities.

I'm also wondering if I'm missing some common Ruby/Perl/Python idiom
for handling in-memory data-structure traversal in a more abstract
way, but so far it doesn't look like it.

Does it make sense to have a general data-structure traversal/query
api in a language like Ruby?

I'd say yes, but maybe only for certain types (DOM tree nodes) - not
necessarily for general Hash, Array and the like. OTOH you can cook up
something quite easily though:

class Object
def traverse() yield self end
end

module Enumerable
def traverse(&b)
each {|o| o.traverse(&b)}
end
end

class Hash
def traverse(&b)
each {|k,v| v.traverse(&b)}
end
end

Note that this does not take care of looks in the object graph. To do that,
you need to do a bit more:

class Object
def traverse(context = {}) context[self.id] ||= (yield self; true) end
end

module Enumerable
def traverse(context = {}, &b)
unless context[self.id]
context[self.id] = true
each {|o| o.traverse(context, &b)}
end
end
end

class Hash
def traverse(context = {}, &b)
unless context[self.id]
context[self.id] = true
each {|k,v| v.traverse(context, &b)}
end
end
end

Kind regards

robert

That looks pretty good.

Thanks,
Nick

 

[Nicholas Van Weerdenburg]

Well, my analogy to writing Ruby was off the mark, but I suppose I was doing
my rant to your "what's not to like about XML" rant. Because (3) is
definitely something I dislike about the XML (and it sounds like you would
agree too).

I had trouble understanding point 3, but I'm guessing your point was
that XSLT shouldn't be an XML dialect, but rather a proper language?

Similar to:
http://www.martinfowler.com/bliki/MovingAwayFromXslt.html

Nick