code: public static String whereVersion(Class<?> entityClass) {
          Set<EntityColumn> columnSet = EntityHelper.getColumns(entityClass);
          boolean hasVersion = false;
          String result = "";
          for (EntityColumn column : columnSet) {
              if (column.getEntityField().isAnnotationPresent(Version.class)) {
                  if (hasVersion) {
                      throw new VersionException(entityClass.getCanonicalName() + " 中包含多个带有 @Version 注解的字段，一个类中只能存在一个带有 @Version 注解的字段!");
                  }
                  hasVersion = true;
                  result = " AND " + column.getColumnEqualsHolder();
              }
          }
          return result;
      }
docs: 乐观锁字段条件
  
  @param entityClass
  @return