我有 c# android 應用程序。我有一個表單，其中包含一些字段 jobno、路線、成本，當用戶填寫表單并按保存時，信息將存儲在應用程序的 SQLite 數據庫中。我想做的是在 if 檢查記錄是否存在時添加一個 if 語句；如果沒有添加條目，則不添加記錄。這是用戶單擊保存按鈕時的代碼。    Record photo = new Record()    {        Jobno = jobno.Text,        route= route.Text,        cost= cost.Text,        Timestamp = timestamp.Timestamp,    };    using (SQLite.SQLiteConnection conn = new SQLite.SQLiteConnection(App.DB_PATH))    {        //check if records exist        conn.CreateTable<Record>();        var numberofrows = conn.Insert(record);        if (numberofrows > 0)        {            DisplayAlert("Success", "record has been saved successfully", "Ok");            MainImage.Source = " ";        }        else        {            DisplayAlert("Failure", "Error occoured while saving record", "Try again");        }    }如何添加 if 語句以僅在不存在時添加新記錄。提前致謝編輯問題    using (SQLite.SQLiteConnection conn = new SQLite.SQLiteConnection(App.DB_PATH))    {        //check if records exist        conn.CreateTable<Record>();        var items = conn.Table<Record>().Where(array => array.Jobno == photo.Jobno && array.Applicationletter == photo.Applicationletter && array.Signno == photo.Signno);        if (items == null)        {            var numberofrows = conn.Insert(photo);            if (numberofrows > 0)            {                DisplayAlert("Success", "record has been saved successfully", "Ok");                MainImage.Source = " ";            }            else            {                DisplayAlert("Failure", "Error occoured while saving record", "Try again");            }        }        else        {            DisplayAlert("Failure", "Photo already exist", "ok");        }        //clear the notes field        notesentry.Text = "";    }