ASP.net, how to make my dropdownlist - asp.net

Question

I have a dropdownlist on my ASP.net page. It contains the primary key values from another table. It is using these values to put into a new, intersection table.
My problem is that, for readability/usability, displaying the primary keys themselves is not ideal. I would prefer to display the corresponding name field, but insert the primary key all the same. I have tried changing the datatextfield and leaving the value field as the pk and selecting either or both columns, but when I try to input it comes back as saying that a null value cannot be accepted.
Can anyone help please?
<InsertItemTemplate>
<asp:DropDownList ID="DropDownList4" runat="server" DataSourceID="SqlDataSource4" DataTextField="BoatID" DataValueField="BoatID">
</asp:DropDownList>
<asp:SqlDataSource ID="SqlDataSource4" runat="server" ConnectionString="<%$ ConnectionStrings:Rowing ClubConnectionString %>" SelectCommand="SELECT [BoatID] FROM [Boat]"></asp:SqlDataSource>
</InsertItemTemplate>
Thank you!
The following is the error page that comes up when trying to add to the table when the datatextfield has been changed to boat name and the sql includes the boat name column:
Server Error in '/' Application.
Cannot insert the value NULL into column 'BoatID', table 'Rowing Club.dbo.SessionBoats'; column does not allow nulls. INSERT fails.
The statement has been terminated.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Data.SqlClient.SqlException: Cannot insert the value NULL into column 'BoatID', table 'Rowing Club.dbo.SessionBoats'; column does not allow nulls. INSERT fails.
The statement has been terminated.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace:
[SqlException (0x80131904): Cannot insert the value NULL into column 'BoatID', table 'Rowing Club.dbo.SessionBoats'; column does not allow nulls. INSERT fails.
The statement has been terminated.]
System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action1 wrapCloseInAction) +1767866
System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action1 wrapCloseInAction) +5352418
System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose) +244
System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady) +1691
System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString) +269
System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, SqlDataReader ds) +1406
System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource1 completion, Int32 timeout, Task& task, Boolean asyncWrite) +177
System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean asyncWrite) +205
System.Data.SqlClient.SqlCommand.ExecuteNonQuery() +160
System.Web.UI.WebControls.SqlDataSourceView.ExecuteDbCommand(DbCommand command, DataSourceOperation operation) +380
System.Web.UI.WebControls.SqlDataSourceView.ExecuteInsert(IDictionary values) +399
System.Web.UI.DataSourceView.Insert(IDictionary values, DataSourceViewOperationCallback callback) +81
System.Web.UI.WebControls.DetailsView.HandleInsert(String commandArg, Boolean causesValidation) +365
System.Web.UI.WebControls.DetailsView.HandleEvent(EventArgs e, Boolean causesValidation, String validationGroup) +584
System.Web.UI.WebControls.DetailsView.OnBubbleEvent(Object source, EventArgs e) +89
System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +37
System.Web.UI.WebControls.DetailsViewRow.OnBubbleEvent(Object source, EventArgs e) +80
System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +37
System.Web.UI.WebControls.LinkButton.OnCommand(CommandEventArgs e) +121
System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument) +156
System.Web.UI.WebControls.LinkButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +9528682
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1724