我可以将 const 对象传递给 ODB 中的 db.persist 吗?
Can I pass a const object to db.persist in ODB?
我正在尝试 ODB ORM,我必须坚持使用一个接口,所以我需要获取一个 const 对象并将其持久化。我不确定 ODB API 是否允许保留 const 对象,因为某些部分似乎为此做好了准备,但它不起作用。
我在这里收到来自 gcc 的错误:
void OdbReportRW::write_object(const MyObject &my_object)
{
odb::core::transaction t{db->begin()};
db->persist(my_object);
t.commit();
}
这是错误,我认为它说 my_object 不应该是 const:
In file included from /usr/local/include/odb/database.hxx:632:0,
from odb_report.hpp:21,
from src/vcf/odb_report.cpp:18:
/usr/local/include/odb/database.txx: In instantiation of ‘typename odb::object_traits<T>::id_type odb::database::persist_(T&) [with T = const MyObject; odb::database_id DB = (odb::database_id)5u; typename odb::object_traits<T>::id_type = long unsigned int]’:
/usr/local/include/odb/database.ixx:167:45: required from ‘typename odb::object_traits<T>::id_type odb::database::persist(const T&) [with T = MyObject; typename odb::object_traits<T>::id_type = long unsigned int]’
src/vcf/odb_report.cpp:134:26: required from here
/usr/local/include/odb/database.txx:38:39: error: no matching function for call to ‘odb::object_traits_impl<MyObject, (odb::database_id)5u>::persist(odb::database&, const MyObject&)’
object_traits::persist (*this, obj);
^
/usr/local/include/odb/database.txx:38:39: note: candidate is:
In file included from src/vcf/odb_report.cpp:27:0:
my-object-error-odb.hxx:247:5: note: static void odb::access::object_traits_impl<MyObject, (odb::database_id)1u>::persist(odb::database&, odb::access::object_traits<MyObject>::object_type&)
persist (database&, object_type&);
^
my-object-odb.hxx:247:5: note: no known conversion for argument 2 from ‘const MyObject’ to ‘odb::access::object_traits<MyObject>::object_type& {aka MyObject&}’
与 clang 相同的错误,更具描述性:
In file included from src/vcf/odb_report.cpp:18:
In file included from inc/vcf/odb_report.hpp:21:
In file included from /usr/local/include/odb/database.hxx:632:
/usr/local/include/odb/database.txx:38:36: error: binding of reference to type 'object_type' (aka 'MyObject') to a value of type 'const MyObject' drops qualifiers
object_traits::persist (*this, obj);
^~~
/usr/local/include/odb/database.ixx:167:12: note: in instantiation of function template specialization 'odb::database::persist_<const MyObject, 5>' requested here
return persist_<const T, id_common> (obj);
^
src/vcf/odb_report.cpp:134:13: note: in instantiation of function template specialization 'odb::database::persist<MyObject>' requested here
db->persist(my_object);
^
inc/vcf/error-odb.hxx:247:37: note: passing argument to parameter here
persist (database&, object_type&);
^
但是,我可以在数据库接口(来自 odb)中看到提供了两种类型的 persist:reference 和 const reference(以及其他带指针的):
// in odb/database.hxx
template <typename T>
typename object_traits<T>::id_type
persist (T& object);
template <typename T>
typename object_traits<T>::id_type
persist (const T& object);
我看到当 class 中没有要持久化的默认构造函数(这里是 MyObject)时,会引发类似的错误(对于 find
,而不是 persist
),但它是在那里,所以这不是问题。我已经检查过默认构造函数只在生成的代码中生成一个额外的方法find
。
它在我的 write_object
方法中删除了 const 说明符,但正如我所说,我必须坚持使用接口。
有任何持久化 const 对象的想法吗?
更彻底地阅读文档我发现了这个 (http://www.codesynthesis.com/products/odb/doc/manual.xhtml#3.8):
The first persist() function expects a constant reference to an instance being persisted. The second function expects a constant object pointer. Both of these functions can only be used on objects with application-assigned object ids (Section 14.4.2, "auto").
事实上,我正在使用 auto
数据库处理 ID 的说明符:
// class MyObject
#pragma db id auto
unsigned long id_;
看来我不能同时使用 auto id 和 const 引用。
我正在尝试 ODB ORM,我必须坚持使用一个接口,所以我需要获取一个 const 对象并将其持久化。我不确定 ODB API 是否允许保留 const 对象,因为某些部分似乎为此做好了准备,但它不起作用。
我在这里收到来自 gcc 的错误:
void OdbReportRW::write_object(const MyObject &my_object)
{
odb::core::transaction t{db->begin()};
db->persist(my_object);
t.commit();
}
这是错误,我认为它说 my_object 不应该是 const:
In file included from /usr/local/include/odb/database.hxx:632:0,
from odb_report.hpp:21,
from src/vcf/odb_report.cpp:18:
/usr/local/include/odb/database.txx: In instantiation of ‘typename odb::object_traits<T>::id_type odb::database::persist_(T&) [with T = const MyObject; odb::database_id DB = (odb::database_id)5u; typename odb::object_traits<T>::id_type = long unsigned int]’:
/usr/local/include/odb/database.ixx:167:45: required from ‘typename odb::object_traits<T>::id_type odb::database::persist(const T&) [with T = MyObject; typename odb::object_traits<T>::id_type = long unsigned int]’
src/vcf/odb_report.cpp:134:26: required from here
/usr/local/include/odb/database.txx:38:39: error: no matching function for call to ‘odb::object_traits_impl<MyObject, (odb::database_id)5u>::persist(odb::database&, const MyObject&)’
object_traits::persist (*this, obj);
^
/usr/local/include/odb/database.txx:38:39: note: candidate is:
In file included from src/vcf/odb_report.cpp:27:0:
my-object-error-odb.hxx:247:5: note: static void odb::access::object_traits_impl<MyObject, (odb::database_id)1u>::persist(odb::database&, odb::access::object_traits<MyObject>::object_type&)
persist (database&, object_type&);
^
my-object-odb.hxx:247:5: note: no known conversion for argument 2 from ‘const MyObject’ to ‘odb::access::object_traits<MyObject>::object_type& {aka MyObject&}’
与 clang 相同的错误,更具描述性:
In file included from src/vcf/odb_report.cpp:18:
In file included from inc/vcf/odb_report.hpp:21:
In file included from /usr/local/include/odb/database.hxx:632:
/usr/local/include/odb/database.txx:38:36: error: binding of reference to type 'object_type' (aka 'MyObject') to a value of type 'const MyObject' drops qualifiers
object_traits::persist (*this, obj);
^~~
/usr/local/include/odb/database.ixx:167:12: note: in instantiation of function template specialization 'odb::database::persist_<const MyObject, 5>' requested here
return persist_<const T, id_common> (obj);
^
src/vcf/odb_report.cpp:134:13: note: in instantiation of function template specialization 'odb::database::persist<MyObject>' requested here
db->persist(my_object);
^
inc/vcf/error-odb.hxx:247:37: note: passing argument to parameter here
persist (database&, object_type&);
^
但是,我可以在数据库接口(来自 odb)中看到提供了两种类型的 persist:reference 和 const reference(以及其他带指针的):
// in odb/database.hxx
template <typename T>
typename object_traits<T>::id_type
persist (T& object);
template <typename T>
typename object_traits<T>::id_type
persist (const T& object);
我看到当 class 中没有要持久化的默认构造函数(这里是 MyObject)时,会引发类似的错误(对于 find
,而不是 persist
),但它是在那里,所以这不是问题。我已经检查过默认构造函数只在生成的代码中生成一个额外的方法find
。
它在我的 write_object
方法中删除了 const 说明符,但正如我所说,我必须坚持使用接口。
有任何持久化 const 对象的想法吗?
更彻底地阅读文档我发现了这个 (http://www.codesynthesis.com/products/odb/doc/manual.xhtml#3.8):
The first persist() function expects a constant reference to an instance being persisted. The second function expects a constant object pointer. Both of these functions can only be used on objects with application-assigned object ids (Section 14.4.2, "auto").
事实上,我正在使用 auto
数据库处理 ID 的说明符:
// class MyObject
#pragma db id auto
unsigned long id_;
看来我不能同时使用 auto id 和 const 引用。