Re: [boost] sqlpp11: SQL for C++

Subject: Re: [boost] sqlpp11: SQL for C++
From: Roland Bock (rbock_at_[hidden])
Date: 2013-11-11 15:14:39

On 2013-11-11 16:30, Bjorn Reese wrote:
> On 11/09/2013 11:03 PM, Roland Bock wrote:
>
>> recently put it on github, and I would really like to hear from you guys
>> whether this is something that could be interesting for you personally
>> or for boost?
>
> I think it could be a very useful addition.
Thanks :-)
>
> There are two potential extensions that may be worth considering. I do
> not consider these extensions required for adoption in Boost, but it may
> be a good idea to at least have given them some thought.
>
> First, make sqlpp11 work on arbitrary data structures. For instance, SQL
> is just one data provider in LINQ.
I haven't given this much thought yet, but I believe that this should be
possible by using a different connector. sqlpp11 itself has no idea
about evaluating the query. In particular, it does not know anything
about database connections.
It constructs a query for you which you then can run. And if your result
has the correct type, you can interpret it using sqlpp11's result object.

Whether the evaluation happens with a database, or by analyzing some XML
or JSON, is totally up to the connector.

Of course, as mentioned elsewhere, it might be useful to create a query
representation which is not a string in those cases :-)
>
> Second, consider adding streaming SQL. Rx is an example of this. This
> could be done with a Boost.Asio integration.
>
>   http://rx.codeplex.com/
I just heard about Rx for the first time the other day, so let me see if
I get the idea right: Instead of querying a database or a given XML
file, you evaluate the query against a stream of incoming data. If a row
matches, you call a callback with the selected data?

If that's the general idea, I think that can be done as well: A library
for evaluating incoming data would get some representation of the
template expression and maybe the result_row type.

In my opinion, both extensions could be done in additional libraries
that make use of the query expressions generated by sqlpp11. A few
additions to the interface should be sufficient.

>
>>    * define types representing tables and columns,
>
> There seems to be room for improvement here. You should consider an
> integration with Boost.Fusion. This way you can avoid having to build
> a code generator.

There seems to be a great deal of demand for using Boost.Fusion for the
Table/Column types.

It would be great if someone could lend me a hand with this. I am going
to update the information in the wiki on what kind information sqlpp11
requires asap (hopefully this weekend).

PS:
In the mail you forwarded me this morning you also asked if I were aware
of N3612?

  http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3612.pdf

Yes, and I agree with most of the described requirements and wanted to
throw my hat in the ring. Personally, I believe that the EDSL-approach
is the way to pursue. Falling back to string based is always possible, a
library like sqlpp11 does not prevent that.