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.

2 files changed, 142 insertions, 58 deletions

diff --git a/odb/sqlite/query.cxx b/odb/sqlite/query.cxx
index 16d8cc2..c3fd31e 100644
--- a/odb/sqlite/query.cxx
+++ b/odb/sqlite/query.cxx
@@ -128,6 +128,10 @@ namespace odb
     // query
     //
 
+    // query
+    //
+    const query query::true_expr (true);
+
     query::
     query (const query& q)
         : clause_ (q.clause_),
@@ -197,6 +201,56 @@ namespace odb
       parameters_->add (p);
     }
 
+    static bool
+    check_prefix (const string& s)
+    {
+      string::size_type n;
+
+      // It is easier to compare to upper and lower-case versions
+      // rather than getting involved with the portable case-
+      // insensitive string comparison mess.
+      //
+      if (s.compare (0, (n = 5), "WHERE") == 0 ||
+          s.compare (0, (n = 5), "where") == 0 ||
+          s.compare (0, (n = 6), "SELECT") == 0 ||
+          s.compare (0, (n = 6), "select") == 0 ||
+          s.compare (0, (n = 8), "ORDER BY") == 0 ||
+          s.compare (0, (n = 8), "order by") == 0 ||
+          s.compare (0, (n = 8), "GROUP BY") == 0 ||
+          s.compare (0, (n = 8), "group by") == 0 ||
+          s.compare (0, (n = 6), "HAVING") == 0 ||
+          s.compare (0, (n = 6), "having") == 0)
+      {
+        // It either has to be an exact match, or there should be
+        // a whitespace following the keyword.
+        //
+        if (s.size () == n || s[n] == ' ' || s[n] =='\t')
+          return true;
+      }
+
+      return false;
+    }
+
+    void query::
+    optimize ()
+    {
+      // Remove a single TRUE literal or one that is followe by one of
+      // the other clauses. This avoids usless WHERE clauses like
+      //
+      // WHERE TRUE GROUP BY foo
+      //
+      clause_type::iterator i (clause_.begin ()), e (clause_.end ());
+
+      if (i != e && i->kind == clause_part::boolean && i->bool_part)
+      {
+        clause_type::iterator j (i + 1);
+
+        if (j == e ||
+            (j->kind == clause_part::native && check_prefix (j->part)))
+          clause_.erase (i);
+      }
+    }
+
     const char* query::
     clause_prefix () const
     {
@@ -204,33 +258,8 @@ namespace odb
       {
         const clause_part& p (clause_.front ());
 
-        if (p.kind == clause_part::native)
-        {
-          const string& s (p.part);
-          string::size_type n;
-
-          // It is easier to compare to upper and lower-case versions
-          // rather than getting involved with the portable case-
-          // insensitive string comparison mess.
-          //
-          if (s.compare (0, (n = 5), "WHERE") == 0 ||
-              s.compare (0, (n = 5), "where") == 0 ||
-              s.compare (0, (n = 6), "SELECT") == 0 ||
-              s.compare (0, (n = 6), "select") == 0 ||
-              s.compare (0, (n = 8), "ORDER BY") == 0 ||
-              s.compare (0, (n = 8), "order by") == 0 ||
-              s.compare (0, (n = 8), "GROUP BY") == 0 ||
-              s.compare (0, (n = 8), "group by") == 0 ||
-              s.compare (0, (n = 6), "HAVING") == 0 ||
-              s.compare (0, (n = 6), "having") == 0)
-          {
-            // It either has to be an exact match, or there should be
-            // a whitespace following the keyword.
-            //
-            if (s.size () == n || s[n] == ' ' || s[n] =='\t')
-              return "";
-          }
-        }
+        if (p.kind == clause_part::native && check_prefix (p.part))
+          return "";
 
         return "WHERE ";
       }
@@ -244,7 +273,9 @@ namespace odb
       string r;
 
       for (clause_type::const_iterator i (clause_.begin ()),
-             end (clause_.end ()); i != end; ++i)
+             end (clause_.end ());
+           i != end;
+           ++i)
       {
         char last (!r.empty () ? r[r.size () - 1] : ' ');
 
@@ -281,10 +312,62 @@ namespace odb
             r += p;
             break;
           }
+        case clause_part::boolean:
+          {
+            if (last != ' ' && last != '(')
+              r += ' ';
+
+            r += i->bool_part ? "1" : "0";
+            break;
+          }
         }
       }
 
       return clause_prefix () + r;
     }
+
+    query
+    operator&& (const query& x, const query& y)
+    {
+      // Optimize cases where one or both sides are constant truth.
+      //
+      bool xt (x.const_true ()), yt (y.const_true ());
+
+      if (xt && yt)
+        return x;
+
+      if (xt)
+        return y;
+
+      if (yt)
+        return x;
+
+      query r ("(");
+      r += x;
+      r += ") AND (";
+      r += y;
+      r += ")";
+      return r;
+    }
+
+    query
+    operator|| (const query& x, const query& y)
+    {
+      query r ("(");
+      r += x;
+      r += ") OR (";
+      r += y;
+      r += ")";
+      return r;
+    }
+
+    query
+    operator! (const query& x)
+    {
+      query r ("NOT (");
+      r += x;
+      r += ")";
+      return r;
+    }
   }
 }
diff --git a/odb/sqlite/query.hxx b/odb/sqlite/query.hxx
index c712b58..a3c63ba 100644
--- a/odb/sqlite/query.hxx
+++ b/odb/sqlite/query.hxx
@@ -121,14 +121,17 @@ namespace odb
         {
           column,
           param,
-          native
+          native,
+          boolean
         };
 
         clause_part (kind_type k): kind (k) {}
         clause_part (kind_type k, const std::string& p): kind (k), part (p) {}
+        clause_part (bool p): kind (boolean), bool_part (p) {}
 
         kind_type kind;
         std::string part;
+        bool bool_part;
       };
 
       query ()
@@ -142,7 +145,7 @@ namespace odb
       query (bool v)
         : parameters_ (new (details::shared) query_params)
       {
-        clause_.push_back (clause_part (clause_part::native, v ? "1" : "0"));
+        clause_.push_back (clause_part (v));
       }
 
       explicit
@@ -203,6 +206,26 @@ namespace odb
       parameters () const;
 
     public:
+      bool
+      empty () const
+      {
+        return clause_.empty ();
+      }
+
+      static const query true_expr;
+
+      bool
+      const_true () const
+      {
+        return clause_.size () == 1 &&
+          clause_.front ().kind == clause_part::boolean &&
+          clause_.front ().bool_part;
+      }
+
+      void
+      optimize ();
+
+    public:
       template <typename T>
       static val_bind<T>
       _val (const T& x)
@@ -370,36 +393,14 @@ namespace odb
       return r;
     }
 
-    inline query
-    operator&& (const query& x, const query& y)
-    {
-      query r ("(");
-      r += x;
-      r += ") AND (";
-      r += y;
-      r += ")";
-      return r;
-    }
+    query
+    operator&& (const query&, const query&);
 
-    inline query
-    operator|| (const query& x, const query& y)
-    {
-      query r ("(");
-      r += x;
-      r += ") OR (";
-      r += y;
-      r += ")";
-      return r;
-    }
+    query
+    operator|| (const query&, const query&);
 
-    inline query
-    operator! (const query& x)
-    {
-      query r ("NOT (");
-      r += x;
-      r += ")";
-      return r;
-    }
+    query
+    operator! (const query&);
 
     // query_column
     //