Re: Gee 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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