Re: [Vala] vala libgda LINQ

[Daniel Espinosa <esodan gmail com>]

2013/12/3 Juarez Rudsatz <juarezr gmail com>

> I checked the samples and some parts of the code.
> Nice work. :-)
>
> Regarding language support, it seems to remain a good amount of work to be
> done yet.
Do you mean Vala features right?

> I'm counting the language features that will be necessary:
> - Object serialization
Are you mean write some where. For XML serialization we have Vala's GXml
project[1]. On GXml's serialization branch, you'll find my work on GObject
serialization to XML, comparable with .NET but, I think more flexible[2].

> - Anonymous types
- Expression and type introspection
> - Type aliasing...
> - Syntax changes
>
>
> At the end a Collection have objects with a set of properties, a SELECT
expression is a filter of that set of objects and a set of properties. They
could be stored in a DbRecord (as for libgda's GdaData [3] ) to save memory
and adding something like "Methods_With_Syntax_Support" [4] , Vala compiler
could transform:

     var selection = select name, salary from employees where id = "123";
     stdout.printf (@"$(selection.name) / $(selection.salary)");

to:
       var _tmp_ = new ArrayList<Employee> ();
       _tmp_.add_all ( ((Traversable) employees).filter(
                              (g)=>{ return id.equals (g) true : false; });
       var selection = ((Selectable) _tmp_).get_fields ("name", "salary");
       if (selection.size != 1)
          throw new SelectableError.MULTIPLE_VALUES_TO_SINGLE ("...");
       var _tmp2_ = selection[0].get_field("name");
       var _tmp3_ = selection[0].get_field("salary");
       stdout.printf (@"$(_tmp2_) / $(_tmp3_)");

> What level of support you are planning?
Because I haven't used LINQ before, I don't know most of its features. Just
think about to allow:

a) Use a SQL like syntax to filter objects and properties, by adding
support to Vala compiler to generate corresponding Vala or C code
b) Object collection must implement at least Gee.Collection and its items
must be Gee.Comparable and Selectable
c) Add a Selectable interface to Gee to allow introspect objects properties
and create a Collection with desired DbRecord set of values.

I don't think mimic LINQ is correct. May we can do better, but is necessary
to define use cases.

The only one I have in mind is:

a) select {list-of-fields} from {collection-object} where {condition}

For this simple expression Vala's compiler should generate required code to:

a) Check for collection-object is a GObject implementing Gee.Collection and
its elements must be Gee.Comparable and Selectable
b) Check for list-of-fields are public properties in collection-object
c) Check for condition is using collection-object 's public properties
d) Generate a Predicate<G> delegate function to find object required objects
e) Fill a Gee.Collection with filtered objects
f) Generate a Gee.Collection from Selectable, that produce rows and
values/columns (with name=properties' name)

> It would be well received by upstream developers?
Really don't know. I'm CC to Vala and Gee lists to hear them about this
idea.

> I'm planning a new architecture for ouro next applications and considering
> vala. But the type safety and language support are the strengths of linq we
> really appreciate.
>
> I'm planning to help someway, but I have a long way yet to be produtive.
>
> Regards
>
> Juarez
[1] https://git.gnome.org/browse/gxml
[2] https://git.gnome.org/browse/gxml/log/?h=serialization
[3] https://git.gnome.org/browse/libgda/tree/libgda/data
[4]
https://wiki.gnome.org/Projects/Vala/Tutorial#Methods_With_Syntax_Support



>  Em 03/12/2013 16:35, "Daniel Espinosa" <esodan gmail com> escreveu:
>
> You can see a preview of my work on current stable libgda.
> > I've finished interfaces and implementations under GdaData name space.
> >
> > I've added some documentation just use --enable-vala-extensions --gtk-doc
> > (some other switches are required) to see it installed.
> >
> > Missed Selectable interface or implementation.
> >
> > I would like to add syntax support on Vala compiler in order to have LINQ
> > like one.
> >
> > For now is very easy to access to data using GdaData objects, see unit
> > tests for more examples.
> > El dic 3, 2013 10:03 a.m., "Juarez Rudsatz" <juarezr gmail com> escribió:
> >
> > > Hi,
> > >
> > > I found that you have been working in a possible implementation of LINQ
> > > in vala [1].
> > > I see that you have made good progress regarding this support.
> > > I want to know what is the current status.
> > > What's missing yet? How is the work for getting basic support ?
> > >
> > > Regards
> > >
> > > Juarez
> > >
> > > [1]
> > > https://mail.gnome.org/archives/vala-list/2011-December/msg00140.html


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