MySQL query example explanation through instantiated object parameters

public static string QueryByEntity<T>(T t) where T : new()
{ string resultstr = string.Empty;
  MySqlDataReader reader = null; try
  {
    Type type = typeof(T);
    PropertyInfo[] properties = type.GetProperties(); string select = string.Format("Select * from {0} {1}", type.Name, "{0}"); string where = string.Empty; foreach (PropertyInfo property in properties)
    { var value = t.GetPropertyValue<T>(property); if (value != null && !value.Equals(property.GetDefaultValue()))
      { if (string.IsNullOrEmpty(where))
        { where = string.Format(" where {0}='{1}' ", property.Name, value);
        } else
        { where = string.Format("{0} and {1} = '{2}'", where, property.Name, value);
        }
      }
    } select = string.Format(select, where);
 
    MySqlConnection connection = OpenConnection(); if (connection == null) return resultstr;
    MySqlCommand _sqlCom = new MySqlCommand(select, connection);
    reader = _sqlCom.ExecuteReader();
    List<T> tList = new List<T>(); while (reader.Read())
    {
      T t1 = new T(); foreach (PropertyInfo property in properties)
      { if (!string.IsNullOrEmpty(reader[property.Name].ToString()))
        {
          property.SetMethod.Invoke(t1, new object[] { reader[property.Name] });
        }
      }
      tList.Add(t1);
    }
    resultstr = JsonConvert.SerializeObject(tList);
  } catch (Exception ex)
  {
    Logging.Error(string.Format("Query database failed, {0}", ex.Message));
  } finally
  { if (reader != null)
    {
      reader.Close();
      reader.Dispose();
    }
  } return resultstr;
}internal static class ObjectExtend
{ public static object GetPropertyValue<T>(this object obj, PropertyInfo property)
  {
    Type type = typeof(T);
    PropertyInfo propertyInfo = type.GetProperty(property.Name); if (propertyInfo != null)
    { return propertyInfo.GetMethod.Invoke(obj, null);
    } return null;
  } public static object GetDefaultValue(this PropertyInfo property)
  { return property.PropertyType.IsValueType ? Activator.CreateInstance(property.PropertyType) : null;
  }
}