how to build up the library..

[Marco Leise]

Am 07.10.2011, 09:26 Uhr, schrieb Russel Winder <russel at russel.org.uk>:

> On Fri, 2011-10-07 at 08:49 +0200, Jacob Carlborg wrote:
> [ . . . ]
>> I think it's important to support the range interface (or if it's
>> simpler, the array interface). I think ActiveRecord has a good high
>> level API which allows to lazily evaluate SQL queries.
>>
>> persons = Person.all # no query is performed here
>> persons = persons.where("name = 'Joe'") # or here
>>
>> persons.each do |p| # The actual query is performed here
>>      # do something with each Person
>> end
>>
>> I don't think it would be strange to see something like this:
>>
>> Person.where("age > 10").map{ |p| p.name } # using "map" on an SQL query
>
> Not just Ruby an Rails with ActiveRecord.  Groovy/Grails/GORM does what
> is basically the same.  Python cannot do the same in the same way Ruby
> and Groovy can, but it has it equivalent (augmented with SQLAlchemy).
> Basically it comes down to constructing dynamic queries using the
> dynamic and MOP nature of the languages.  The crucial keyword here is
> Builder.  The trick is that what looks like function call is actually
> interpreted via the builder/MOP as the construction of a data structure,
> which then creates the query on demand -- with template placeholder
> filling as required.
>
> Does D have the reflection capabilities to do this in any way, shape or
> form similar tp the way the dynamic languages do it?

This has already been done in D. There is a nice library that assembles  
queries at compile time and fetches results lazily into structs. The name?  
Sorry, I forgot. But the author will probably show up here.