将datetime插入为字符串C＃SQL-server

Question

I have a SQL-server and a column called CitizenshipDate . That column is of type datetime in the SQL.

However, the problem is that it can have the value '0' which is NOT a datetime value but rather a string value.

So what I'm trying to do is to handle it as a string in C# when inserting it values but get the error:

Conversion failed when converting datetime from character string.

I get that error because I'm trying to insert string into a datetime in the SQL-server.

Here is my code:

 class Person {
       public string PersonalIdentityNumber { get; set; }
       public string SpecialIdentityNumber { get; set; }
       public string FirstName { get; set; }
       public string LastName { get; set; }
       public string CitizenshipDate { get; set; }

}



  List<FolkbokforingspostTYPE> deserializedList = new List<FolkbokforingspostTYPE>();
            deserializedList = Deserialize<List<FolkbokforingspostTYPE>>();


            var myPersons = Deserialize<List<FolkbokforingspostTYPE>>()
                .Select(x => new Person
                {
                    PersonalIdentityNumber = x.Personpost.PersonId.PersonNr,
                    SpecialIdentityNumber = x.Personpost.PersonId.Tilltalsnamnsmarkering != null ? x.Personpost.PersonId.Tilltalsnamnsmarkering : null, 
                    LastName = x.Personpost.Namn.Efternamn,
                    FirstName = x.Personpost.Namn.Fornamn,
                    CitizenshipDate = x.Personpost.Medborgarskap != null ? x.Personpost.Medborgarskap.Medborgarskapsdatum : null             

                });



            string connetionString = null;


            SqlDataAdapter adpter = new SqlDataAdapter();
            DataSet ds = new DataSet();
            XmlReader xmlFile;



            connetionString = "Data Source=tsrv2062;Initial Catalog=Bums;User ID=BumsUser;Password=2tusen7Bums";


            xmlFile = XmlReader.Create("navetout.xml", new XmlReaderSettings());
            ds.ReadXml(xmlFile);


            using (var connection = new SqlConnection(connetionString))
            {
                connection.Open();
                DateTime datum = DateTime.Now;
                string LastChangedBy = "System";

                foreach (Person p in myPersons)
                {

                    SqlCommand command1 = Avreg(p.UnregistrationReason, p.GivenNameNumber,p.ProtectedIdentity, p.CitizenshipDate, connection);


                    command1.Parameters.AddWithValue("@PersonalIdentityNumber", string.Format("{0}{1}", p.PersonalIdentityNumber, p.SpecialIdentityNumber));
                    command1.Parameters.AddWithValue("@FirstName", p.FirstName);
                    command1.Parameters.AddWithValue("@LastName", p.LastName);
                    command1.ExecuteNonQuery();

                    Console.WriteLine(string.Format("{0}{1}", p.PersonalIdentityNumber, p.SpecialIdentityNumber));


                }
            }

            Console.WriteLine("Done");


           // }// Put a break-point here, then mouse-over PersonalIdentityNumber...  deserializedList contains everything if you need it
           //catch (Exception)
           // {

           //     throw;
           // }
            Console.ReadKey();
        }

        public static SqlCommand Avreg(string s, string t, string p, string c, SqlConnection connection)
        {
            var query = "UPDATE Seamen SET FirstName = @FirstName, "+
                "LastName = @LastName, "+

            SqlCommand command1;


//Here is the `CitizenshipDate` 
            if (c == "0")
            {
                query += ", CitizenshipDate = '0'";
                command1 = new SqlCommand(query, connection);
                command1.Parameters.Clear();



            }
            else
            {
                query += ", CitizenshipDate = @CitizenshipDate";
                command1 = new SqlCommand(query, connection);
                command1.Parameters.Clear();
                command1.Parameters.AddWithValue("@CitizenshipDate", c ?? DBNull.Value.ToString());

            }


//Ignore these if statements
             if ((!string.IsNullOrEmpty(s)) && !string.IsNullOrEmpty(t))
            {

            }
            else
            {

                    query += ", GivenNameNumber = @GivenNameNumber WHERE PersonalIdentityNumber = @PersonalIdentityNumber";
                    t = "00";
                    command1 = new SqlCommand(query, connection);
                    command1.Parameters.Clear();
                    command1.Parameters.AddWithValue("@GivenNameNumber", t ?? DBNull.Value.ToString());

                    return command1;

            }
             return command1;
        }

Please note that I cannot change the type in the database. I somehow need a way to insert the value from String. Can someone help ?

Answer 1

If the column does not allow nulls, then you can use NULL to represent "0", and then in code, when loading the record, replace NULL with "0" in the UI. Or, if you do allow NULLS and need another value to represent "0", you can use an arbitrary date you wouldn't normally use like '1/1/1753' (the lowest value for SQL datetime) or '1/1/1900' (lowest for smalldatetime) or something like that. Any date that is these dates represents "0". So the conversion to "0" happens within the app, not stored in the database.

Answer 2

If your column supports null you can fix it like this:

        if (c == "0")
        {
            query += ", CitizenshipDate = NULL--instead of '0'";

If it does not support NULL values you will have to insert a default value such as DateTime.MinValue.