template < class T >

class TypeHandler

Library: Data
Package: DataCore
Header: Poco/Data/TypeHandler.h


Converts Rows to a Type and the other way around. Provide template specializations to support your own complex types.

Take as example the following (simplified) class: class Person { private: std::string _lastName; std::string _firstName; int _age; public: const std::string& getLastName(); [...] // other set/get methods (returning const reference), a default constructor, [...] // optional < operator (for set, multiset) or function operator (for map, multimap) };

The TypeHandler must provide a custom bind, size, prepare and extract method:

template <> class TypeHandler<struct Person> { public: static std::size_t size() {

return 3; // lastName + firstname + age occupy three columns


static void bind(std::size_t pos, const Person& obj, AbstractBinder::Ptr pBinder, AbstractBinder::Direction dir) {

// the table is defined as Person (LastName VARCHAR(30), FirstName VARCHAR, Age INTEGER(3))
// Note that we advance pos by the number of columns the datatype uses! For string/int this is one.
poco_assert_dbg (!pBinder.isNull());
TypeHandler<std::string>::bind(pos++, obj.getLastName(), pBinder, dir);
TypeHandler<std::string>::bind(pos++, obj.getFirstName(), pBinder, dir);
TypeHandler<int>::bind(pos++, obj.getAge(), pBinder, dir);


static void prepare(std::size_t pos, const Person& obj, AbstractPreparator::Ptr pPreparator) {

// the table is defined as Person (LastName VARCHAR(30), FirstName VARCHAR, Age INTEGER(3))
poco_assert_dbg (!pPreparator.isNull());
TypeHandler<std::string>::prepare(pos++, obj.getLastName(), pPreparator);
TypeHandler<std::string>::prepare(pos++, obj.getFirstName(), pPreparator);
TypeHandler<int>::prepare(pos++, obj.getAge(), pPreparator);


static void extract(std::size_t pos, Person& obj, const Person& defVal, AbstractExtractor::Ptr pExt) {

// defVal is the default person we should use if we encunter NULL entries, so we take the individual fields
// as defaults. You can do more complex checking, ie return defVal if only one single entry of the fields is null etc...
poco_assert_dbg (!pExt.isNull());
std::string lastName;
std::string firstName;
int age = 0;
// the table is defined as Person (LastName VARCHAR(30), FirstName VARCHAR, Age INTEGER(3))
TypeHandler<std::string>::extract(pos++, lastName, defVal.getLastName(), pExt);
TypeHandler<std::string>::extract(pos++, firstName, defVal.getFirstName(), pExt);
TypeHandler<int>::extract(pos++, age, defVal.getAge(), pExt);

} };

Note that the TypeHandler template specialization must always be declared in the namespace Poco::Data. Apart from that no further work is needed. One can now use Person with into and use clauses.


Direct Base Classes: AbstractTypeHandler

All Base Classes: AbstractTypeHandler

Member Summary

Member Functions: bind, extract, prepare, size

Inherited Functions: operator =


Member Functions

bind static inline

static void bind(
    std::size_t pos,
    const T & obj,
    AbstractBinder::Ptr pBinder,
    AbstractBinder::Direction dir

extract static inline

static void extract(
    std::size_t pos,
    T & obj,
    const T & defVal,
    AbstractExtractor::Ptr pExt

prepare static inline

static void prepare(
    std::size_t pos,
    const T & obj,
    AbstractPreparator::Ptr pPreparator

size static inline

static std::size_t size();