How to Change a Page Title in a Database

[guixingzhe]

I have created a repeat template, which title is @ Today xxx, in a datebase. The method UpdateProperty is used for change Title. But something wrong after run the method, that is body.properties.Title.title[0].mention.date.start should be defined. So I try to adding a RichTextMention property to solve it , and the proplem occurs

internal class DailyTrackerPage
    {
        public string Title { get; set; }
        public bool? Done { get; set; }
        public DateTime CreatedTime { get; set; }
        public RichTextMention Mention { get; set; }
        public DailyTrackerPage(Page page)
        {
            CreatedTime = page.CreatedTime;
            Done = page.Properties[nameof(Done)] is FormulaPropertyValue formula ? formula.Formula.Boolean : default;
            TitlePropertyValue? title1 = page.Properties[nameof(Title)] as TitlePropertyValue;
            Mention = title1.Title.FirstOrDefault() is RichTextMention mention ? mention : default;
            DateTime dateTime = Convert.ToDateTime(Mention.PlainText);
            Mention.Mention.Date = new DatePropertyValue { Date = new Date { Start = dateTime } };
            Title = page.Properties[nameof(Title)] is TitlePropertyValue title
                ? string.Join(null, title.Title.Select(x => x.PlainText))
                : string.Empty;
        }
    }

private static async Task UpdateProperty(Page? page)
        {
            if (page != null)
            {
                DailyTrackerPage trackerPage = new(page);
                var newTitle = new List<RichTextBase> { { trackerPage.Mention }, { new RichTextBase { PlainText = "Voc30" } } };
                if (trackerPage.Title.Contains("Voc"))
                {
                    await Console.Out.WriteLineAsync($"Title{trackerPage.Title} ID：{page.Id}").ConfigureAwait(false);
                    await MyClient.Client.Pages.UpdatePropertiesAsync(page.Id, new Dictionary<string, PropertyValue>
                    {
                        { "Title", new TitlePropertyValue() { Title =  newTitle } }
                    }).ConfigureAwait(false);
                }
            }
        }