MWSupport for custom data types in dbo library
Added by Michael Wagner over 16 years ago
How can I implement a custom data type in addition to the types already supported by the dbo library? In particular I would need a boolean type that I can map to a PostgreSQL "boolean" type. I created a class "BooleanType" that inherits from the sql_value_traits class but now I am stuck:
class BooleanType : public dbo::sql_value_traits< bool, void >
...
...
Is there any example around?
Many thanks,
Michael
Replies (2)
KD RE: Support for custom data types in dbo library - Added by Koen Deforche over 16 years ago
Hey Michael,
The traits class should describe properties about your particular type through specialization for your type:
Header file:
template<>
struct sql_value_traits<bool, void>
{
static const bool specialized = true;
static const char *type(SqlConnection *conn, int size);
static void bind(bool v, SqlStatement *statement, int column, int size);
static bool read(bool& v, SqlStatement *statement, int column, int size);
};
Implementation:
const char *sql_value_traits<bool>::type(SqlConnection *conn, int size)
{
return "boolean not null";
}
void sql_value_traits<bool>::bind(bool v,
SqlStatement *statement, int column,
int size)
{
statement->bind(column, static_cast<int>(v ? 1 : 0));
}
bool sql_value_traits<bool>::read(bool& v,
SqlStatement *statement, int column,
int size)
{
int value;
bool notNull = statement->getResult(column, &value);
if (notNull)
v = value;
return notNull;
}
I think the bool type could actually be supported by the library itself...
MW RE: Support for custom data types in dbo library - Added by Michael Wagner over 16 years ago
You guys are really helpful, thanks a lot!!!
Another way that I tried works as well since the PostgreSQL "boolean" can be mapped to a string:
Header:
...
private:
std::string transparent_;
public:
template
void persist(Action& a)
{
dbo::field(a, transparent_, "transparent"); // "transparent" column is of type "boolean"
...
}
CPP:
...
void Layer::setTransparent(bool transparent)
{
transparent_ = transparent ? "true" : "false";
}
bool Layer::getTransparent()
{
return transparent_ = "true" ? true : false;
}