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Insert empty DateTime from C# into FoxPro

I am trying to insert an empty DateTime into a FoxPro database using DbParameter in C#. Our application marries FoxPro data along with SQL Server and .NET models/data.
My current issue is that most of our DateTime types in C# are not nullable, nor should they be. However, most of our legacy data in FoxPro are empty dates (shown as ' / / : : '). I am trying to do an insert into the FoxPro table where I do a check to see if the .NET DateTime meets certain criteria, then inserts an empty date. This last part has proven to be a nightmare.
What I have tried so far:
.Parameters.Add(string.Empty, new DateTime())
The above understandably inserts 01/01/0001 but is not what we want.
.Parameters.Add(string.Empty, "{}")
.Parameters.Add(string.Empty, "{:://}")
.Parameters.Add(string.Empty, "{//}")
.Parameters.Add(string.Empty, "'{}'")
The above all result in
System.Data.OleDb.OleDbException: 'Data type mismatch'.
which makes sense because I'm trying to send a string to a field with DateTime type.
Does anyone know how to insert an empty DateTime into FoxPro?

If I'm understanding you correctly, you're not using a DbParameter, but rather an OleDbParameter, and you're adding them through the OleDbParameterCollection.Add method?
If so, consider that you are using the overload that is .Add(String, Object), and you could instead use the overload that is .Add(String, OleDbType):
.Parameters.Add(string.Empty, OleDbType.Date)
The default value of an OleDbParameter is null, so you don't need to do anything more for your empty dates.
Also, depending on how the column is defined in your FoxPro database schema, it may be appropriate to pass OleDbType.Date, OleDbType.DBDate, OleDbType.DBTime, or OleDbType.DBTimeStamp. The full list of OleDB types is documented here, but I'm not entirely certain how they align to FoxPro's data types.

I believe your second example is close, but you have the Date and Time portions reversed.
It should be .Parameters.Add(string.Empty, "{//::}")
The // represent the Date portion, and the :: the Time portion.

Not sure of your SQL-Insert statement for VFP, but you MAY need to adjust it and do TWO different inserts. One IF a date exists, another if it does not.
For the one that does NOT have a date, I would hard-enter the following (for example where the "?" are the parameter place-holders)
insert into yourTable ( fld1, fld2,..., YourDateField ) values ( ?, ?, ..., ctot('') )
the function CTOT() means character to datetime and an empty string will comply with expected VFP Date/time field.

Work for me.
Parameters.AddWithValue("CreateDate", new DateTime(1899,12,30,0,0,0));

c# SQL Server : DATETIME datatype

I am writing a unit test which stores an object with a DateTime parameter into a DATETIME2 SQL Server database column. I then create a temporary DateTime object called new_date_time and set that value to DateTime.Now.
The new_date_time value is then used to update the previous value and the SQL query to do this completes successfully.
When re-reading the object back from the database I receive the correct datetime values for days/hours/minutes but the .Ticks value is different from the new_date_time variables .Ticks property. The value returned from the read call returns the last 4 digits of the .Ticks property as zeros.
Why is this rounding occurring making my Assert.AreEqual fail?? :)
Thanks

I guess you are using Parameters.AddWithValue when writing the date to Sql Server. From MSDN the inferred type of a CLR DateTime is SqlDbType.DateTime and not SqlDbType.DateTime2 so the precision is being lost when writing your date to the database.
Explicitly setting the type to datetime2 will solve the issue. For example:
command.Parameters.AddWithValue("#now", DateTime.Now).SqlDbType =
SqlDbType.DateTime2;
Edit
#marc_s makes a good point with his comment:
You should read (and embrace!) Can we stop using AddWithValue() already?
To avoid these kind of issues from biting you, you could get into the habit of using the Add method on the parameters collection which takes the SqlDbType in some overloads and then set the Value property on that rather than using the AddWithValue method:
command.Parameters.Add("#now", SqlDbType.DateTime2).Value = DateTime.Now;

Maybe your database field is not storing your entire DateTime.Now value, because it's not precise enough. Why don't you simply compare your dates after you've formatted them as you like?
eg: (untested):
var databaseDate = d1.ToString("MM/dd/yyyy HH:mm:ss.fff");
var tempDate = d2.ToString("MM/dd/yyyy HH:mm:ss.fff");
Assert.AreEqual(databaseDate, tempDate);
I tested: using Linq To Entities My DateTime.Now is correctly saved to my datetime2(7) and equality test return True.
Are you sure you're passing your correct datetime value to the database? without truncating it?

Error when trying to update values in database

I have the following c#/Query:
TrackDuration =TimeSpan.Parse( Request.Form["TrackDuration"].ToString());
string InsertQuery = string.Format("UPDATE tblTracks SET TrackLength={0}, TrackDuration='{1}', TrackName='{2}',TrackDescription='{3}',TrackMap='{4}',DifficultLevel={5},OverallHeight={6},IsCircular='{7}', ForBeginners='{8}',StartPoint='{9}',ParkingPlace='{10}',SeasonOfYear={11},TrackLocation={12}, Images='{13}' WHERE UserID={14}",
TrackLength, TrackDuration, TrackName, TrackDescription, TrackMap, DifficultID, OverallHeight, IsCircular, ForBeginners, StartPoint, ParkingPlace, SeasonID, AreaID, ImageList, UserID);
But I got this error message:
Syntax error in UPDATE statement
Syntax error (missing operator) in query expression
I realy tried to solve this, but I can't.
How can I fix this problem?
Update:
This is the value of the Query:
UPDATE tblTracks SET TrackLength=35, TrackDuration='02:30:00', TrackName='45',TrackDescription='<p>sometext.</p>
',TrackMap='f',DifficultLevel=3,OverallHeight=450,IsCircular='true', ForBeginners='false',StartPoint='<p>קיבוץיסעור </p>
',ParkingPlace='<p>כניסה לקיבוץ יסעור</p>
',SeasonOfYear=1,TrackLocation=3, Images='' WHERE UserID=1
The sql values types are:
TrackLength = number ; TrackDuration = date/time ; TrackName= string ;TrackDescription= string; TrackMap = string; DifficultLevel=number;OverallHeight=number;IsCircular=true/false;ForBeginners=true/false;
StartPoint=string; ParkingPlace=string; SeasonOfYear=number; TrackLocation=number;Images=string

'02:30:00' is not a correct value for datetime DB field, AFAIK. The default format is controlled by date format setting.
Additionally, '20130412' should work in any case, but for datetime field. You need to format the TrackDuration correctly or use CAST/CONVERT. As TimeSpan doesn't contain date part (it represents a duration and not a point in time), you can only make it up (e.g. prepend "20100101") but that is an awful hack.
The proper solution is to use the correct DB field type.
'02:30:00' might work if the field was of time type. Please read some more about time types in SQL Server.
Even better, why don't you use plain integer for the duration in seconds? The duration is not a date anyway.
The much bigger issue is that you are concatenating strings to set the command text, which opens you for SQL injection attack. If I name the racing track a';DROP TABLE tblTracks;-- your database is toast:
UPDATE tblTracks SET TrackLength=35,
TrackDuration='02:30:00',
TrackName='a';DROP TABLE tblTracks;-- ...

Error in inserting statement when inserting

I am working on c# project and using winform.
Here the problem is the query was working previously but now it is not working
Here the todaydate is a datetimePicker which is set to short date format
and my datatype of column is smalldatetime the error i am getting is
The conversion of a nvarchar data type to a
smalldatetime data type resulted in an out-of-range value.
The statement has been terminated.
if i have two date time picker one for date and second for time then how can i insert? please can you guide me

AddWithValue determines the datatype of the parameter from the value you pass.
In your case you are passing a string and thus the parameter is passed to the database as a string not as a datetime expected by the database
you should change that line
cmd.Parameters.AddWithValue("#today", todaydate.Value);

You're currently passing in the text value, which means something else is having to then parse it as a date. Don't do that. Given that you've got a DateTimePicker, you should just use the DateTime value it provides:
cmd.Parameters.AddWithValue("#today", todaydate.Value);
... or create the parameter first with a specific type (SqlDbType.SmallDateTime), then set the value using todaydate.Value. The important point is to avoid the string conversion.
Wherever possible, you should avoid converting values into text. Keep them in their "natural" form (e.g. DateTime in this case) for as much of the time as possible: on input, parse into the natural form, and if you can avoid ever converting to a string, do so!

I think your time7 column in database is smalldatetime and you tried to assign it a string. I don't suggest it.
Try with Add() method like this;
command.Parameters.Add("#today", SqlDbType.SmallDatetime);
command.Parameters["#today"].Value = todaydate.Value;
or you can use AddWithValue() as also like this;
cmd.Parameters.AddWithValue("#today", todaydate.Value);

DateTime Insert via LINQ

I have a column in my table which has a DataType of 'timestamp'. Now I am inserting a row through LINQ2SQL. Now what should I write here:
Entity_Product_Point ev = new Entity_Product_Point();
ev.DateCreated = ???
Thanks!

Are you SURE you wanted timestamp? It has nothing to do with dates... If you'd like to store "DateCreated", I think you probably want to use either a DateTime or just Date datatype in MSSQL. If that's what you really intended, then you can pass in DateTime.Now for a value.

Well the corresponding type would be byte[], but this type is used internally by SQL Server for row versioning—and by ORMs for optimistic locking. You should never (can't) write a value out for a timestamp column manually.
For a more complete listing of which type correspond to what, check out this question