fixup! Support evaluation of DateTime.Now on db side

Add an option for failing or falling back in case of lack of dialect
support

Author: fredericDelaporte

doc/reference/modules/configuration.xml

@@ -734,14 +734,39 @@ var session = sessions.OpenSession(conn);
                             <para>
                                 The new pre-evaluation allows them to be converted to HQL function calls which will be run on the db
                                 side. This allows by example to retrieve the server time instead of the client time, or to generate
-                                GUIDs for each row instead of an unique one for all rows. (This does not happen if the dialect does
-                                not support the required HQL function.)
+                                GUIDs for each row instead of an unique one for all rows.
                             </para>
                             <para>
                                 The new pre-evaluation will likely be enabled by default in the next major version (6.0).
                             </para>
                         </entry>
                     </row>
+                    <row>
+                        <entry>
+                            <literal>linqtohql.fallback_on_preevaluation</literal>
+                        </entry>
+                        <entry>
+                            When the new pre-evaluation is enabled, should methods which translation is not supported by the current
+                            dialect fallback to pre-evaluation? Defaults to <literal>false</literal>.
+                            <para>
+                                <emphasis role="strong">eg.</emphasis> 
+                                <literal>true</literal> | <literal>false</literal>
+                            </para>
+                            <para>
+                                When this fallback option is enabled while legacy pre-evaluation is disabled, properties or functions
+                                like <literal>DateTime.Now</literal> or <literal>Guid.NewGuid()</literal> used in Linq expressions
+                                will not fail when the dialect does not support them, but will instead be pre-evaluated.
+                            </para>
+                            <para>
+                                When this fallback option is disabled while legacy pre-evaluation is disabled, properties or functions
+                                like <literal>DateTime.Now</literal> or <literal>Guid.NewGuid()</literal> used in Linq expressions
+                                will fail when the dialect does not support them.
+                            </para>
+                            <para>
+                                This option has no effect if the legacy pre-evaluation is enabled.
+                            </para>
+                        </entry>
+                    </row>
                     <row>
                         <entry>
                             <literal>sql_exception_converter</literal>