Add odb::connection class

This abstract class represents a connection to the database. One can
use it to start a transaction or to execute a native statement out
of a transaction.

Before we had concrete connection classes in the database runtime
libraries (e.g., odb::mysql::connection). Now these classes derive
from odb::connection.

1 files changed, 18 insertions, 5 deletions

diff --git a/odb/database.hxx b/odb/database.hxx
index bc7a10b..c4458d9 100644
--- a/odb/database.hxx
+++ b/odb/database.hxx
@@ -15,6 +15,7 @@
 #include <odb/forward.hxx>
 #include <odb/query.hxx>
 #include <odb/result.hxx>
+#include <odb/connection.hxx>
 #include <odb/exceptions.hxx>
 
 #include <odb/details/export.hxx>
@@ -152,19 +153,31 @@ namespace odb
     unsigned long long
     execute (const std::string& statement);
 
-    virtual unsigned long long
-    execute (const char* statement, std::size_t length) = 0;
+    unsigned long long
+    execute (const char* statement, std::size_t length);
+
+    // Transactions.
+    //
+  public:
+    transaction_impl*
+    begin ();
 
-    // Transaction API.
+    // Connections.
     //
   public:
-    virtual transaction_impl*
-    begin () = 0;
+    connection_ptr
+    connection ();
 
   protected:
     database ();
 
   protected:
+    typedef odb::connection connection_type;
+
+    virtual connection_type*
+    connection_ () = 0;
+
+  protected:
     template <typename T>
     typename object_traits<T>::id_type
     persist_ (const typename object_traits<T>::pointer_type&);