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

On 2013-11-11 01:47, Larry Evans wrote:

On 11/10/13 18:02, Larry Evans wrote:

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On 11/09/13 16:03, Roland Bock wrote:

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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

[snip] The code here:

https://github.com/rbock/sqlpp11/blob/master/include/sqlpp11/table_base.h

contains:

template struct table_base_t : public ColumnSpec::_name_t::template _member_t>... {...};

which looks like it declares a table row, where the columns come from ColumnSpec...

In understanding how the library works, this is probably one of the crucial parts. As you guessed correctly, it declares the innards of a table class. The somewhat convoluted looking inheritance adds columns as members to the class. The column_t instantiates a column class with all required information like the value type, whether it can be NULL, its textual representation, etc. The ColumnSpec also contains a template like this: template<typename T> struct _member_t { T foo; }; Inheriting from an instance of this template adds a member with the respective name (foo in this example) to derived class. Thus, the code you cited adds objects representing columns as appropriately named members to the table class. The same technique is used when creating aliases for expressions, using selects as pseudo tables and constructing result row classes.

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What's confusing to me is the code here:

https://github.com/rbock/sqlpp11/wiki/Tables

contains, what I assume are the ColumnSpecs; however, there's no column_t, there's only column_type. Does table_base.h have a typo?

OOPS. I see it now:

https://github.com/rbock/sqlpp11/blob/master/include/sqlpp11/column.h

I guess that part of the confusion is due to names. I know that the code has inconsistent use of _type and _t suffix, which certainly doesn't help and is on my list of todos. Having column_t and a member class _column_type is probably also adding to the confusion. Maybe renaming _column_type to _column_traits_t would be better? Best regards, Roland