From 2fbd31985a169c9c6a212460a01d0a78805933e3 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Sun, 2 Oct 2011 17:07:20 +0200
Subject: If query substituting placeholder is empty, pass true expression
 instead

This allows uniform usage of views both with and without any extra
conditions. Also optimize some common cases so that we don't have
useless WHERE TRUE clauses or (...) AND (TRUE) expressions.
---
 odb/relational/source.cxx |  2 +-
 odb/relational/source.hxx | 20 +++++++++++++++-----
 2 files changed, 16 insertions(+), 6 deletions(-)

(limited to 'odb/relational')

diff --git a/odb/relational/source.cxx b/odb/relational/source.cxx
index 5dfc15a..fe23ac9 100644
--- a/odb/relational/source.cxx
+++ b/odb/relational/source.cxx
@@ -499,7 +499,7 @@ namespace relational
 
                 if (tt == CPP_CLOSE_PAREN)
                 {
-                  r += 'q';
+                  r +=  "q.empty () ? query_base_type::true_expr : q";
                   *placeholder = true;
                 }
                 else
diff --git a/odb/relational/source.hxx b/odb/relational/source.hxx
index fbe9b1c..4d120db 100644
--- a/odb/relational/source.hxx
+++ b/odb/relational/source.hxx
@@ -3082,8 +3082,8 @@ namespace relational
               if (p != string::npos)
               {
                 ph = true;
-                os << strlit (string (vq.literal, 0, p + 1))
-                   << " + q + "
+                os << strlit (string (vq.literal, 0, p + 1)) << " +" << endl
+                   << "(q.empty () ? query_base_type::true_expr : q) +" << endl
                    << strlit (string (vq.literal, p + 2));
               }
               else
@@ -3564,14 +3564,17 @@ namespace relational
                 if (p != string::npos)
                 {
                   ph = true;
-                  os << strlit (string (vq.literal, 0, p + 1))
-                     << " + q + "
+                  os << strlit (string (vq.literal, 0, p + 1))<< " +" << endl
+                     << "(q.empty () ? query_base_type::true_expr : q) +" << endl
                      << strlit (string (vq.literal, p + 2));
                 }
                 else
                   os << strlit (vq.literal);
+
+                os << ");";
               }
               else
+              {
                 // Output the pragma location for easier error tracking.
                 //
                 os << "// From " <<
@@ -3581,7 +3584,14 @@ namespace relational
                    << translate_expression (
                      c, vq.expr, vq.scope, vq.loc, "query", &ph).value;
 
-              os << ");";
+                os << ");";
+
+                // Optimize the query if it had a placeholder. This gets
+                // rid of useless clauses like WHERE TRUE.
+                //
+                if (ph)
+                  os << "c.optimize ();";
+              }
 
               if (!ph)
                 os << "c += q;";
-- 
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