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March 24, 2008
Rails-like Model in D (making it "automagical")
I've been throwing ideas around in my head for my pet project, ConYard (http://www.fsdev.net/wiki/conyard), and I'm not sure how to implement this in D.  I don't really know how to implement it in any language, so I thought I'd ask for some advice.

I want to create a model system similar to, though perhaps not necessarily as "automagical" as the models from Ruby on Rails.  I want a system that the programmer can extend to create a database-independent object that serializes to a database.  The problem I'm grappling with is how to make it so that the user doesn't have to hand-code everything, and can make the implementation more readable.

I'm not sure how to handle the model's fields.  I want the fields to be D types, eg. char[] and int and float and all that.  I also want for those types to serialize to the SQL database, without the user having to write all that nonsense by hand.

I need a way to somehow flag a field in a model as an element that needs to be serialized to a database.  From there it's fairly simple work of writing code that makes SQL statements based on input.  It's so simple, it scares me into over complicating it.

I'm not sure how to start about this.  I was thinking of some kind of static this () statement that the user has to fill in, and somehow "register" all the elements (that'll be in the database).  Then calls to functions that push/pull data to/from the database could call another function that the user doesn't have to touch, which takes all those elements from the model instance and generates the SQL queries (or uses a previously generated one) to make the data move.

It still seems like a lot of overhead to me, like a lot of boring stuff that the programmer has to type in all the time.  Imagine a library where you have to do something annoying like registerElement(IntElement(this.myfield)); in a static constructor all the time?  (IntElement would be some kind of element class that would know how to take a D int and make it to a SQL int, and then you could possibly write your own to take types that you make and translate them into SQL types, or serializations that fit into SQL types, etc).

There must be a better way.  I've scanned through the D 1.00 specification document a few times and come up dry.  If anyone has any suggestions of things I might try, or even examples of techniques that I could use, I'd really appreciate it!
March 24, 2008
Re: Rails-like Model in D (making it "automagical")
So, you have a year of time and are interrested to implement a RAD 
system around enterprise patterns ?  :)

Rails :
As you know Rails is based on the active record pattern.
I found it remarkable that all "actice record" implementations (I know 
about) are script based. Ruby, Groovy, PHP.

I am sceptical regarding a pure D implementation. Maybe embedding MiniD 
  is a reasonable solution.

But you want RAD / DWT / Tango :

My advice is a) not to use the active record pattern and b) wait for DWT 
3.4  // google SWT 3.4 databinding

To create a RAD you have to bind the GUI elements like entry fields, 
checkboxes etc. to a db entity. (at least)
IMO The only reasonable solution is using the MVC pattern. Beside, it is 
not nessesary to sepereate View Controler.
In other words the good ol' Subject-Observer pattern. I can imagine that 
 probabely Tango's Signal-Slot can be used too. (Have to think about)

What to use instead of active record ?
DAO Data Access Objects, have a look at the Java implementation. or 
google for Java DAO

In general DAO is build arround the 1) Singleton pattern and 2) the 
factory pattern. (IMO the prototype pattern is the better choice)
DDBI is somewhat similar.

Consider code generation . In other words you need a tool to scan the DB 
System tables and generate D source code - classes which implement ORM 
using the factory method pattern (ORM ->object relational mapping).

The best source reagarding real world pattern is :
http://www.dofactory.com/Patterns/Patterns.aspx
(C# code. Allmost a piece of cake to port)

Sorry, for this unstructured message, but actually I have nearly zero 
time for programming. Bjoern






Chris Miller schrieb:
> I've been throwing ideas around in my head for my pet project, ConYard (http://www.fsdev.net/wiki/conyard), and I'm not sure how to implement this in D.  I don't really know how to implement it in any language, so I thought I'd ask for some advice.
> 
> I want to create a model system similar to, though perhaps not necessarily as "automagical" as the models from Ruby on Rails.  I want a system that the programmer can extend to create a database-independent object that serializes to a database.  The problem I'm grappling with is how to make it so that the user doesn't have to hand-code everything, and can make the implementation more readable.
> 
> I'm not sure how to handle the model's fields.  I want the fields to be D types, eg. char[] and int and float and all that.  I also want for those types to serialize to the SQL database, without the user having to write all that nonsense by hand.
> 
> I need a way to somehow flag a field in a model as an element that needs to be serialized to a database.  From there it's fairly simple work of writing code that makes SQL statements based on input.  It's so simple, it scares me into over complicating it.
> 
> I'm not sure how to start about this.  I was thinking of some kind of static this () statement that the user has to fill in, and somehow "register" all the elements (that'll be in the database).  Then calls to functions that push/pull data to/from the database could call another function that the user doesn't have to touch, which takes all those elements from the model instance and generates the SQL queries (or uses a previously generated one) to make the data move.
> 
> It still seems like a lot of overhead to me, like a lot of boring stuff that the programmer has to type in all the time.  Imagine a library where you have to do something annoying like registerElement(IntElement(this.myfield)); in a static constructor all the time?  (IntElement would be some kind of element class that would know how to take a D int and make it to a SQL int, and then you could possibly write your own to take types that you make and translate them into SQL types, or serializations that fit into SQL types, etc).
> 
> There must be a better way.  I've scanned through the D 1.00 specification document a few times and come up dry.  If anyone has any suggestions of things I might try, or even examples of techniques that I could use, I'd really appreciate it!
March 24, 2008
Re: Rails-like Model in D (making it "automagical")
DAO Java :
http://java.sun.com/blueprints/corej2eepatterns/Patterns/DataAccessObject.html

at the eof the document you'll find a ref. to the  :
Factory Method [GoF] and Abstract Factory [GoF]

You can use the link in the prev. msg. to see a real world implementation;
hth Bjoern
March 24, 2008
Re: Rails-like Model in D (making it "automagical")
Bjoern schrieb:
> But you want RAD / DWT / Tango :
> 
> My advice is a) not to use the active record pattern and b) wait for DWT 
> 3.4  // google SWT 3.4 databinding

Data binding is a JFace technology.
"JFace Data Binding 1.0 was releaseed with Eclipse 3.3"

http://www.eclipse.org/swt/R3_4/new_and_noteworthy.html
http://wiki.eclipse.org/index.php/JFace_Data_Binding

I don't see how this is a requirement or even related to a "Rail-like 
Model in D" ? So, why "wait for DWT 3.4" ?
March 24, 2008
Re: Rails-like Model in D (making it "automagical")
Frank Benoit schrieb:
> Bjoern schrieb:
>> But you want RAD / DWT / Tango :
>>
>> My advice is a) not to use the active record pattern and b) wait for 
>> DWT 3.4  // google SWT 3.4 databinding
> 
> Data binding is a JFace technology.
> "JFace Data Binding 1.0 was releaseed with Eclipse 3.3"
> 
> http://www.eclipse.org/swt/R3_4/new_and_noteworthy.html


> http://wiki.eclipse.org/index.php/JFace_Data_Binding
quote :
....The core concepts behind the project are Observables and Bindings. 
We provide IObservable implementations for SWT, JFace, and JavaBeans....
end quote
Means IMO :
Binding interfaces have to be be stripped out.

> 
> I don't see how this is a requirement or even related to a "Rail-like 
> Model in D" ? So, why "wait for DWT 3.4" ?
> 

I am wrong with "waiting for 3.4." Sorry :(

However, this discussion also touches DWT event-handling. (your msg on 
Digitalmars.dwt) and it seems to me that the suggested implementation is 
 working well even in case that you have to deal with new, binding- 
related events.

As said,not much time for programming. I am restaurating my "farm" and 
the barnes
March 24, 2008
Re: Rails-like Model in D (making it "automagical")
Chris Miller wrote:
> I've been throwing ideas around in my head for my pet project, ConYard (http://www.fsdev.net/wiki/conyard), and I'm not sure how to implement this in D.  I don't really know how to implement it in any language, so I thought I'd ask for some advice.
> 
> I want to create a model system similar to, though perhaps not necessarily as "automagical" as the models from Ruby on Rails.  I want a system that the programmer can extend to create a database-independent object that serializes to a database.  The problem I'm grappling with is how to make it so that the user doesn't have to hand-code everything, and can make the implementation more readable.
> 
> I'm not sure how to handle the model's fields.  I want the fields to be D types, eg. char[] and int and float and all that.  I also want for those types to serialize to the SQL database, without the user having to write all that nonsense by hand.
> 
> I need a way to somehow flag a field in a model as an element that needs to be serialized to a database.  From there it's fairly simple work of writing code that makes SQL statements based on input.  It's so simple, it scares me into over complicating it.
> 
> I'm not sure how to start about this.  I was thinking of some kind of static this () statement that the user has to fill in, and somehow "register" all the elements (that'll be in the database).  Then calls to functions that push/pull data to/from the database could call another function that the user doesn't have to touch, which takes all those elements from the model instance and generates the SQL queries (or uses a previously generated one) to make the data move.
> 
> It still seems like a lot of overhead to me, like a lot of boring stuff that the programmer has to type in all the time.  Imagine a library where you have to do something annoying like registerElement(IntElement(this.myfield)); in a static constructor all the time?  (IntElement would be some kind of element class that would know how to take a D int and make it to a SQL int, and then you could possibly write your own to take types that you make and translate them into SQL types, or serializations that fit into SQL types, etc).
> 
> There must be a better way.  I've scanned through the D 1.00 specification document a few times and come up dry.  If anyone has any suggestions of things I might try, or even examples of techniques that I could use, I'd really appreciate it!

Ruby ( and Python ) both have run-time reflection built in to their 
language. D does not. I would suggest to you that emulating RAD 
programming with a language which does not have built-in support for 
run-time reflection will be a very hard task for you to accomplish.
March 24, 2008
Re: Rails-like Model in D (making it "automagical")
Edward Diener wrote:

> Chris Miller wrote:
>> I've been throwing ideas around in my head for my pet project, ConYard
>> (http://www.fsdev.net/wiki/conyard), and I'm not sure how to implement
>> this in D.  I don't really know how to implement it in any language, so I
>> thought I'd ask for some advice.
>> 
>> I want to create a model system similar to, though perhaps not
>> necessarily as "automagical" as the models from Ruby on Rails.  I want a
>> system that the programmer can extend to create a database-independent
>> object that serializes to a database.  The problem I'm grappling with is
>> how to make it so that the user doesn't have to hand-code everything, and
>> can make the implementation more readable.
>> 
>> I'm not sure how to handle the model's fields.  I want the fields to be D
>> types, eg. char[] and int and float and all that.  I also want for those
>> types to serialize to the SQL database, without the user having to write
>> all that nonsense by hand.
>> 
>> I need a way to somehow flag a field in a model as an element that needs
>> to be serialized to a database.  From there it's fairly simple work of
>> writing code that makes SQL statements based on input.  It's so simple,
>> it scares me into over complicating it.
>> 
>> I'm not sure how to start about this.  I was thinking of some kind of
>> static this () statement that the user has to fill in, and somehow
>> "register" all the elements (that'll be in the database).  Then calls to
>> functions that push/pull data to/from the database could call another
>> function that the user doesn't have to touch, which takes all those
>> elements from the model instance and generates the SQL queries (or uses a
>> previously generated one) to make the data move.
>> 
>> It still seems like a lot of overhead to me, like a lot of boring stuff
>> that the programmer has to type in all the time.  Imagine a library where
>> you have to do something annoying like
>> registerElement(IntElement(this.myfield)); in a static constructor all
>> the time?  (IntElement would be some kind of element class that would
>> know how to take a D int and make it to a SQL int, and then you could
>> possibly write your own to take types that you make and translate them
>> into SQL types, or serializations that fit into SQL types, etc).
>> 
>> There must be a better way.  I've scanned through the D 1.00
>> specification document a few times and come up dry.  If anyone has any
>> suggestions of things I might try, or even examples of techniques that I
>> could use, I'd really appreciate it!
> 
> Ruby ( and Python ) both have run-time reflection built in to their
> language. D does not. I would suggest to you that emulating RAD
> programming with a language which does not have built-in support for
> run-time reflection will be a very hard task for you to accomplish.

Not a terribly hard thing to get around, given the correct tools.

-- 
Lars Ivar Igesund
blog at http://larsivi.net
DSource, #d.tango & #D: larsivi
Dancing the Tango
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