From 51a01cfebf933d270bf7b7fadb0fb3ca3b7a4cd5 Mon Sep 17 00:00:00 2001
From: Michael Shepanski <michael@codesynthesis.com>
Date: Thu, 6 Nov 2014 16:33:35 +1100
Subject: Implement {query,execute}_{one,value}() shortcut functions

Useful in situations where the query is know to return at most one element
(*_one) or exactly one element (*_value).
---
 query/driver.cxx | 50 +++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 41 insertions(+), 9 deletions(-)

(limited to 'query/driver.cxx')

diff --git a/query/driver.cxx b/query/driver.cxx
index fbd148d..aec8ac8 100644
--- a/query/driver.cxx
+++ b/query/driver.cxx
@@ -22,17 +22,21 @@ typedef odb::query<person> query;
 typedef odb::result<person> result;
 
 static void
-print (result& r)
+print (person& p)
 {
-  for (result::iterator i (r.begin ()); i != r.end (); ++i)
-  {
-    cout << i->first () << " ";
+  cout << p.first () << " ";
 
-    if (!i->middle ().null ())
-      cout << i->middle ().get () << " ";
+  if (!p.middle ().null ())
+    cout << p.middle ().get () << " ";
 
-    cout << i->last () << " " << i->age () << endl;
-  }
+  cout << p.last () << " " << p.age () << endl;
+}
+
+static void
+print (result& r)
+{
+  for (result::iterator i (r.begin ()); i != r.end (); ++i)
+    print (*i);
 
   cout << endl;
 }
@@ -90,7 +94,6 @@ main (int argc, char* argv[])
       //
       /*
       person p ("", "", 0);
-
       for (result::iterator i (r.begin ()); i != r.end (); ++i)
       {
         i.load (p);
@@ -103,6 +106,35 @@ main (int argc, char* argv[])
       t.commit ();
     }
 
+    // Use query_one() as a shortcut when there's no more than one element
+    // in the result.
+    //
+    {
+      transaction t (db->begin ());
+
+      auto_ptr<person> p (db->query_one<person> (query::age == 21));
+
+      if (p.get () != 0)
+      {
+        print (*p);
+        cout << endl;
+      }
+
+      // Or we can load the state into an existing object.
+      //
+      /*
+      person p ("", "", 0);
+
+      if (db->query_one<person> (query::age == 21, p))
+      {
+        print (p);
+        cout << endl;
+      }
+      */
+
+      t.commit ();
+    }
+
     // Query that shows how to combine expressions with &&, ||, and !
     // as well as use paranthesis to control evaluation order.
     //
-- 
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