On 11/12/13, 2:17 PM, Roland Bock wrote:
On 2013-11-12 10:00, Matthijs Möhlmann wrote:
On 11/12/13, 4:26 AM, Tim Keitt wrote:
On Sat, Nov 9, 2013 at 4:03 PM, Roland Bock <rbock@eudoxos.de> wrote:
Hi,
over the last four or five years I developed several SQL libraries for C++. With C++11 I was finally able to create an SQL library that meets my own expectations and requirements. It is being used in production, I 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?
https://github.com/rbock/sqlpp11 https://github.com/rbock/sqlpp11/wiki
sqlpp11 is a template library representing an embedded domain specific language (EDSL) that allows you to
* define types representing tables and columns, * construct type safe queries checked at compile time for syntax errors, type errors, name errors and even some semantic errors, * interpret results by iterating over query-specific structs with appropriately named and typed members.
This results in several benefits, e.g.
* the library user operates comfortably on structs and functions, * the compiler reports many kinds of errors long before the code enters unit testing or production, * the library hides the gory details of string construction for queries and interpreting string based results returned by select calls. I.e. you don't need to use strings in query construction where you wouldn't use them in SQL and there is no need to use positional arguments or to parse strings when obtaining fields from a result row (the latter being true unless you do not know which columns to select at compile time).
The library supports both static and dynamic queries. The former offers greater benefit in terms of type and consistency checking. The latter makes it easier to construct queries on the flight.
Specific traits of databases (e.g. unsupported or non-standard features) are known at compile time as well. This way, the compiler can tell the developer at compile time if a query is not accepted by the database (e.g. if a feature is missing). And the library can form the query in the correct manner, for instance if the engine uses concat instead of operator|| to concatenate strings.
Two Examples: ============= Static Select: -------------- // selecting zero or more results, iterating over the results for (const auto& row : db.run( select(foo.name, foo.hasFun) .from(foo) .where(foo.id > 17 and foo.name.like("%bar%")))) { if (row.name.is_null()) std::cerr << "name will convert to empty string" << std::endl; std::string name = row.name; // text fields are implicitly convertible to string bool hasFun = hasFun; // bool fields are implicitly convertible to bool }
Dynamic Select: ---------------- auto s = dynamic_select(db, tab.foo).dynamic_columns().from(tab); if (userWantsBar) s.add_column(tab.bar); for(const auto& row : run(s)) { std::cerr << "row.foo: " << row.foo; if (userWantsBar) std::cerr << "row.bar" << row.at("bar"); std::cerr << std::endl; };
Please let me know your questions/thoughts/suggestions/rants. Contributions welcome, of course :-)
This is an interesting thread and I thought I'd comment.
I am a pretty heavy user of postgresql/postgis (spatial extension) in my work. I wrote the first R package to access postgresql and contributed to the current R DBI package. I did a proof-of-concept (= not very pretty ;-) embedding of the Boost Graph Library in postgresql replacing local storage with prepared queries called on demand.
I have to say when I look at this, I don't really want to learn another SQL. I am perfectly happy to send query strings to the database and let it parse them. I can debug these separate from my C++ code. I think for complex queries (recursive with anyone?) it would be quite difficult to get the C++ right.
What I would really like is a mapping of binary cursors to iterator concepts + easy type-safe endian-aware customizable data conversion. But that's my bias. I've always liked mapping on-demand data to common interfaces.
But your use cases are probably different and I can see how this would be very useful to some.
THK
Hi,
Isn't libpqxx then not what you are looking for? I know its specifically written for PostgreSQL.
http://pqxx.org/development/libpqxx/
Regards, Matthijs
It also string based, isn't it? For those who'd like to experiment with sqlpp11 and postgreSQL: I just received a mail that there is a first connector library for postgreSQL available:
https://github.com/pbondo/sqlpp11-connector-postgresql
Regards,
Roland
It is string based yes. Nice, I'll experiment with that. Regards, Matthijs