Fix serialization of empty dynamic_where

It was serialized with a dummy expression, which turned out to be
problematic for some vendors, see #282

include/sqlpp11/where.h

@@ -256,6 +256,10 @@ namespace sqlpp
       static_check_t<not std::is_same<Database, void>::value, assert_where_dynamic_used_with_dynamic_statement_t>,
       check_where_t<Expression>>;
 
+  template <typename Database>
+  using check_where_empty_dynamic_t = static_combined_check_t<
+      static_check_t<not std::is_same<Database, void>::value, assert_where_dynamic_used_with_dynamic_statement_t>>;
+
   // NO WHERE YET
   template <bool WhereRequired>
   struct no_where_t
@@ -338,10 +342,11 @@ namespace sqlpp
         return _where_impl<_database_t>(Check{}, expression);
       }
 
-      auto dynamic_where() const -> _new_statement_t<check_where_dynamic_t<_database_t, boolean_operand>,
-                                                     where_t<_database_t, boolean_operand>>
+      auto dynamic_where() const
+          -> _new_statement_t<check_where_empty_dynamic_t<_database_t>, where_t<_database_t, unconditional_t>>
       {
-        return dynamic_where(::sqlpp::value(true));
+        return {static_cast<const derived_statement_t<Policies>&>(*this),
+                where_data_t<_database_t, unconditional_t>{unconditional_t{}}};
       }
 
     private:
@@ -378,6 +383,24 @@ namespace sqlpp
     }
   };
 
+  template <typename Context, typename Database>
+  struct serializer_t<Context, where_data_t<Database, unconditional_t>>
+  {
+    using _serialize_check = consistent_t;
+    using T = where_data_t<Database, unconditional_t>;
+
+    static Context& _(const T& t, Context& context)
+    {
+      if (t._dynamic_expressions.empty())
+      {
+        return context;
+      }
+      context << " WHERE ";
+      interpret_list(t._dynamic_expressions, " AND ", context);
+      return context;
+    }
+  };
+
   template <typename Context>
   struct serializer_t<Context, where_data_t<void, unconditional_t>>
   {
@@ -403,6 +426,13 @@ namespace sqlpp
     return statement_t<Database, no_where_t<false>>().dynamic_where(std::forward<T>(t));
   }
 
+  template <typename Database>
+  auto dynamic_where(const Database & /*unused*/)
+      -> decltype(statement_t<Database, no_where_t<false>>().dynamic_where())
+  {
+    return statement_t<Database, no_where_t<false>>().dynamic_where();
+  }
+
   inline auto unconditionally() -> decltype(statement_t<void, no_where_t<false>>().unconditionally())
   {
     return statement_t<void, no_where_t<false>>().unconditionally();

test_serializer/CMakeLists.txt

@@ -26,12 +26,13 @@ set(test_serializer_names
 	As
 	Blob
 	CustomQuery
-  ForUpdate
-  From
-  In
-  Insert
+	DynamicWhere
+	ForUpdate
+	From
+	In
+	Insert
 	TableAlias
-  Where
+	Where
   )
 
 create_test_sourcelist(test_serializer_sources test_serializer_main.cpp ${test_serializer_names})

test_serializer/DynamicWhere.cpp

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2016-2019, Roland Bock
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ *  * Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+ * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "compare.h"
+#include "Sample.h"
+#include <sqlpp11/sqlpp11.h>
+
+#include <iostream>
+
+int DynamicWhere(int, char*[])
+{
+  const auto bar = test::TabBar{};
+  auto db = MockDb{};
+
+  compare(__LINE__, dynamic_where(db), "");
+  compare(__LINE__, dynamic_where(db, bar.gamma), " WHERE tab_bar.gamma");
+
+  {
+    auto statement = sqlpp::dynamic_where(db);
+    statement.where.add(without_table_check(bar.gamma));
+    compare(__LINE__, statement, " WHERE tab_bar.gamma");
+  }
+
+  {
+    auto statement = dynamic_where(db, bar.gamma);
+    statement.where.add(without_table_check(bar.gamma));
+    compare(__LINE__, statement, " WHERE tab_bar.gamma AND tab_bar.gamma");
+  }
+
+  return 0;
+}

tests/Update.cpp

@@ -66,6 +66,9 @@ int Update(int, char*[])
   auto values = [&t]() { return std::make_tuple(t.delta += t.alpha, t.beta = "no cake this time"); };
 
   db(update(t).set(t.delta = sqlpp::verbatim<sqlpp::integer>("17+4")).unconditionally());
+  db(update(t)
+         .set(t.delta = sqlpp::verbatim<sqlpp::integer>("17+4"))
+         .where(sqlpp::verbatim<sqlpp::text>("'hansi'") == "hansi"));
   db(update(t).set(t.delta = sqlpp::null).unconditionally());
   db(update(t).set(t.delta = sqlpp::default_value).unconditionally());