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Diffstat (limited to 'libodb/odb/prepared-query.hxx')
| -rw-r--r-- | libodb/odb/prepared-query.hxx | 201 |
1 files changed, 201 insertions, 0 deletions
diff --git a/libodb/odb/prepared-query.hxx b/libodb/odb/prepared-query.hxx new file mode 100644 index 0000000..7cac6da --- /dev/null +++ b/libodb/odb/prepared-query.hxx @@ -0,0 +1,201 @@ +// file : odb/prepared-query.hxx +// license : GNU GPL v2; see accompanying LICENSE file + +#ifndef ODB_PREPARED_QUERY_HXX +#define ODB_PREPARED_QUERY_HXX + +#include <odb/pre.hxx> + +#include <odb/forward.hxx> // odb::core +#include <odb/traits.hxx> +#include <odb/result.hxx> +#include <odb/statement.hxx> + +#include <odb/details/export.hxx> +#include <odb/details/shared-ptr.hxx> + +namespace odb +{ + class LIBODB_EXPORT prepared_query_impl: public details::shared_base + { + public: + virtual + ~prepared_query_impl (); + + prepared_query_impl (connection&); + + // Verify this prepared query and the specified transaction use the + // same connection. + // + virtual bool + verify_connection (transaction&); + + bool cached; + connection& conn; + const char* name; + details::shared_ptr<statement> stmt; + details::shared_ptr<result_impl> (*execute) (prepared_query_impl&); + + private: + prepared_query_impl (const prepared_query_impl&); + prepared_query_impl& operator= (const prepared_query_impl&); + + // Doubly-linked list of results. + // + // prev_ == 0 means we are the first element. + // next_ == 0 means we are the last element. + // next_ == this means we are not on the list. + // + protected: + friend class connection; + + void + list_remove (); + + prepared_query_impl* prev_; + prepared_query_impl* next_; + }; + + template <typename T> + struct prepared_query + { + // Cached version. + // + explicit + prepared_query (prepared_query_impl* impl = 0): impl_ (impl) {} + + // Uncached version. + // + explicit + prepared_query (const details::shared_ptr<prepared_query_impl>& impl) + : impl_ (impl.get ()) + { + impl_->_inc_ref (); + } + + result<T> + execute (bool cache = true) + { + typedef + typename result_base<T, class_traits<T>::kind>::result_impl_type + derived_type; + + details::shared_ptr<result_impl> ri (impl_->execute (*impl_)); + result<T> r ( + details::shared_ptr<derived_type> ( + static_cast<derived_type*> (ri.release ()))); + + if (cache) + r.cache (); + + return r; + } + + typename object_traits<T>::pointer_type + execute_one () + { + return execute (false).one (); + } + + bool + execute_one (T& object) + { + return execute (false).one (object); + } + + T + execute_value () + { + // Compiler error pointing here? The object must be default- + // constructible in order to use the return-by-value API. + // + T o; + execute (false).value (o); + return o; + } + + const char* + name () const + { + return impl_->name; + } + + typedef odb::statement statement_type; + + statement_type& + statement () const + { + return *impl_->stmt; + } + + typedef prepared_query_impl* prepared_query::*unspecified_bool_type; + operator unspecified_bool_type () const + { + return impl_ ? &prepared_query::impl_ : 0; + } + + public: + ~prepared_query () + { + if (impl_ != 0 && !impl_->cached && impl_->_dec_ref ()) + delete impl_; + } + + prepared_query (const prepared_query& x) + : impl_ (x.impl_) + { + if (!impl_->cached) + impl_->_inc_ref (); + } + + prepared_query& + operator= (const prepared_query& x) + { + if (impl_ != x.impl_) + { + if (impl_ != 0 && !impl_->cached && impl_->_dec_ref ()) + delete impl_; + + impl_ = x.impl_; + + if (!impl_->cached) + impl_->_inc_ref (); + } + + return *this; + } + + private: + // Ideally, we would just use shared_ptr to manage the impl object. + // However, there is a problem if the prepared query is cached on + // the connection and the connection is released early when the + // transaction is committed or rolled back. In this case, the + // prepared_query object might still be around pointing to impl. If + // this connection and the prepared query are then used by another + // thread while we release the impl object, then we have a race + // condition. + // + // To work around this problem we will simply "reference" the impl + // object without counting if the prepared query is cached. For + // transition from pointer to reference, see cache_query_() in + // connection.cxx. + // + // You may also observe that in order to know whether this is a + // cached prepared query or not, we have to read the cached data + // member in the impl object. This does not cause a race because, + // unlike the reference count, this member is immutable once set + // to true. + // + friend class connection; + prepared_query_impl* impl_; + }; + + namespace common + { + using odb::prepared_query; + } +} + +#include <odb/post.hxx> + +#endif // ODB_PREPARED_QUERY_HXX |