Fix DD4hep compilation

Alignment/AlignKernel/AlignKernel/DetectorElement.h

@@ -107,6 +107,27 @@ namespace LHCb::Alignment {
           de.applyToAllChildren(
               [&func]( LHCb::Detector::DeIOV item ) { func( LHCb::Alignment::DetectorElement{item} ); } ) );
     }
+
+    LHCb::Alignment::DetectorElement getChild( const std::string& part ) {
+#ifdef USE_DD4HEP
+      LHCb::Detector::detail::DeIOVObject* det{nullptr};
+      m_data.applyToAllChildren( [&det, &part]( LHCb::Detector::DeIOV item ) {
+        if ( item.name() == part ) det = item.access();
+      } );
+      if ( det ) return LHCb::Detector::DeIOV( det );
+#else
+      auto it = std::find_if( m_data->childBegin(), m_data->childEnd(), [&part]( const ::IDetectorElement* item ) {
+        auto& name = item->name();
+        return name.length() > part.length() && name.substr( name.length() - part.length() ) == part &&
+               name[name.length() - part.length() - 1] == '/';
+      } );
+      if ( it != m_data->childEnd() ) return dynamic_cast<const ::DetectorElement*>( *it );
+#endif
+      throw GaudiException( "WriteAlignmentConditions : unable to find requested element : no child named " + part +
+                                " was found in " + name(),
+                            "GetElementsToBeAligned:", StatusCode::FAILURE );
+    }
+
     auto size() const { DELEGATE2( de->childIDetectorElements().size(), de.size() ); }
 
     bool operator==( const DetectorElement& other ) const { return m_data == other.m_data; }