From 0fba3bc7e0747e23ca2698e0acc82e80b569e531 Mon Sep 17 00:00:00 2001
From: Constantin Michael <constantin@codesynthesis.com>
Date: Tue, 5 Jul 2011 13:02:03 +0200
Subject: Implement PostgreSQL specific fetch operations for select_statement

---
 odb/pgsql/statement.cxx | 70 +++++++++++++++++++++++++++++++++----------------
 odb/pgsql/statement.hxx | 52 ++++++++++++++++++++++++++++--------
 2 files changed, 89 insertions(+), 33 deletions(-)

diff --git a/odb/pgsql/statement.cxx b/odb/pgsql/statement.cxx
index 233519c..b06646e 100644
--- a/odb/pgsql/statement.cxx
+++ b/odb/pgsql/statement.cxx
@@ -282,7 +282,25 @@ namespace odb
                       native_binding& native_cond,
                       binding& data)
         : statement (conn, name, stmt, types, types_count),
-          cond_ (cond),
+          cond_ (&cond),
+          native_cond_ (native_cond),
+          data_ (data),
+          row_count_ (0),
+          current_row_ (0)
+
+    {
+    }
+
+    select_statement::
+    select_statement (connection& conn,
+                      const std::string& name,
+                      const std::string& stmt,
+                      const Oid* types,
+                      std::size_t types_count,
+                      native_binding& native_cond,
+                      binding& data)
+        : statement (conn, name, stmt, types, types_count),
+          cond_ (0),
           native_cond_ (native_cond),
           data_ (data),
           row_count_ (0),
@@ -295,7 +313,9 @@ namespace odb
     execute ()
     {
       result_.reset ();
-      bind_param (native_cond_, cond_);
+
+      if (cond_ != 0)
+        bind_param (native_cond_, *cond_);
 
       result_.reset (PQexecPrepared (conn_.handle (),
                                      name_.c_str (),
@@ -314,44 +334,50 @@ namespace odb
       current_row_ = 0;
     }
 
+    void select_statement::
+    free_result ()
+    {
+      result_.reset ();
+      row_count_ = 0;
+      current_row_ = 0;
+    }
+
+    bool select_statement::
+    next ()
+    {
+      if (current_row_ <= row_count_)
+        ++current_row_;
+
+      return current_row_ <= row_count_;
+    }
+
     select_statement::result select_statement::
-    fetch ()
+    load ()
     {
-      if (current_row_ >= row_count_)
+      if (current_row_ > row_count_)
         return no_data;
 
       PGresult* h (result_.get ());
 
-      if (bind_result (data_.bind, data_.count, h, current_row_))
-      {
-        ++current_row_;
-        return success;
-      }
-
-      return truncated;
+      assert (current_row_ > 0);
+      return bind_result (data_.bind, data_.count, h, current_row_ - 1) ?
+        success : truncated;
     }
 
     void select_statement::
-    refetch ()
+    reload ()
     {
-      assert (current_row_ < row_count_);
+      assert (current_row_ > 0);
+      assert (current_row_ <= row_count_);
 
       if (!bind_result (data_.bind,
                         data_.count,
                         result_.get (),
-                        current_row_++,
+                        current_row_ - 1,
                         true))
         assert (false);
     }
 
-    void select_statement::
-    free_result ()
-    {
-      result_.reset ();
-      row_count_ = 0;
-      current_row_ = 0;
-    }
-
     //
     // insert_statement
     //
diff --git a/odb/pgsql/statement.hxx b/odb/pgsql/statement.hxx
index 146a34f..09779b4 100644
--- a/odb/pgsql/statement.hxx
+++ b/odb/pgsql/statement.hxx
@@ -36,14 +36,6 @@ namespace odb
       void
       deallocate ();
 
-    protected:
-      statement (connection&,
-                 const std::string& name,
-                 const std::string& stmt,
-                 const Oid* types,
-                 std::size_t types_count);
-
-    protected:
       // Adapt an ODB binding to a native PostgreSQL parameter binding.
       //
       static void
@@ -63,6 +55,13 @@ namespace odb
                    bool truncated = false);
 
     protected:
+      statement (connection&,
+                 const std::string& name,
+                 const std::string& stmt,
+                 const Oid* types,
+                 std::size_t types_count);
+
+    protected:
       connection& conn_;
       std::string name_;
 
@@ -85,6 +84,14 @@ namespace odb
                         native_binding& native_cond,
                         binding& data);
 
+      select_statement (connection& conn,
+                        const std::string& name,
+                        const std::string& stmt,
+                        const Oid* types,
+                        std::size_t types_count,
+                        native_binding& native_cond,
+                        binding& data);
+
       // Common select interface expected by the generated code.
       //
     public:
@@ -112,24 +119,47 @@ namespace odb
       // Load next row columns into bound buffers.
       //
       result
-      fetch ();
+      fetch ()
+      {
+        return next () ? load () : no_data;
+      }
 
       // Reload truncated columns into bound buffers.
       //
       void
-      refetch ();
+      refetch ()
+      {
+        reload ();
+      }
 
       // Free the result set.
       //
       void
       free_result ();
 
+      // Finer grained control of PostgreSQL-specific interface that
+      // splits fetch() into next() and load().
+      //
+    public:
+      // Return false if there is no more rows. You should call next()
+      // until it returns false or, alternatively, call free_result ().
+      // Otherwise the statement will remain unfinished.
+      //
+      bool
+      next ();
+
+      result
+      load ();
+
+      void
+      reload ();
+
     private:
       select_statement (const select_statement&);
       select_statement& operator= (const select_statement&);
 
     private:
-      binding& cond_;
+      binding* cond_;
       native_binding& native_cond_;
 
       binding& data_;
-- 
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