Re: [boost] Interest in an ODBC library?

From: Brock Peabody (brock.peabody_at_[hidden])
Date: 2005-08-27 09:55:38

> On Behalf Of Corwin Joy

> Actually what I am talking about here is the situation where
> the user specifies the type of the target data at compile
> time.

I think what we have with the binding language isn't so much type safety
as it is type consistency.  If you specify that two fields are related
with the binding language, we can ensure at compile time that they are
the same types, for example.

You could continue this with the query building language:

 field<std::string> name("Name");
 field<double> salary("Salary");

 BindEmployee(Employee &Emp, Bindings &cols) {
     cols[name] >> emp.Name;
     cols[salary] >> emp.Salary;
 }

   //compile time error
 std::string criteria = make_criteria(name == salary);

Of course this is a little clumsy especially in that you lose automatic
type deduction but maybe it would be worth it in some cases.

> Personally, I quite like using operators for the binding syntax rather
> than
> function calls since I think this make it much easier to read what is
> going
> on.

I agree.

> Here is a second quickie example
> 
> // simple example for Local bindings ... read a map
> 
> map<string, double> ReadDataLocalBCASingleField()
> {
>     typedef pair<string, double> rowtype;    rowtype row;  //
prototype

We've been down some of the same paths.  As it turns out almost
everything I read from a database is read into a map.  I got so tired of
doing this that I finally wrote a map_pair_type<> template.

> row
> object to guide binding process    // declare our bindings locally
> 
>     DBView<rowtype> view("EMPLOYEES",
>         BCA(row, COLS["Name"] >> row.first && COLS["Salary"] >>
row.second
> )
>     );
> 
>     // copy the doubles from the view into the vector and return
>     map<string, double> results(view.begin(), view.end());
>     return results;
> }

In my language this looks like:

 const serializer<rowtype> ser =
   table("EMPLOYEES") [
      field("Name") = &rowtype::first,
      field("Salary") = &rowtype::second
   ];

 return ser.load<map<string, double> >(database);

Very similar!