Table is nullable DateTime, but DataSet throws an exception?

Question

I\'m attempting to use the DataSet designer to create a datatable from a query. I got this down just fine. The query used returns a nullable datetime column from the datab

Answer 1

To make this work with LINQ you will have to go to the Tables properties in your dataset.xsd. First look and make sure that the column is indeed set to nullable. THEN you must look at specific property "NullValue" for the column. Null Value defaults to "Exception", at least in VS 2012. Set it to Nothing for VB such that you can do "IsNot Nothing" in the LINQ Where clause.

Answer 2

In DataSet Designer, use System.Object data type instead of System.DateTime and set NullValue to (Null) and DefaultValue to <DBNull> and when it is needed, convert it such as:

var row1 = dateSet1.table1.FirstOrDefault();
if (row1 == null)
    return;
DateTime? date = (DateTime?) row1.ObjectDate;

Answer 3

The System.DateTime Object is not nullable. To make a DateTime nullable make it a DateTime? (put a ? after DateTime)

DateTime? nullableDateTime = null;

Answer 4

I am using the code listed below to handle null cells in an Excel sheet that is read in to a datatable.

if (!reader.IsDBNull(0))                                
{                                    
  row["DateOnCall"] = (DateTime)reader[0];
}

Answer 5

Typed data sets don't support nullable types. They support nullable columns.

The typed data set generator creates non-nullable properties and related methods for handling null values. If you create a MyDate column of type DateTime and AllowDbNull set to true, the DataRow subclass will implement a non-nullable DateTime property named MyDate, a SetMyDateNull() method, and an IsMyDateNull() method. This means that if you want to use a nullable type in your code, you have to do this:

DateTime? myDateTime = myRow.IsMyDateNull() ? null : (DateTime?) row.MyDate;

While this doesn't totally defeat the purpose of using typed data sets, it really sucks. It's frustrating that typed data sets implement nullable columns in a way that's less usable than the System.Data extension methods, for instance.

Is particularly bad because typed data sets do use nullable types in some places - for instance, the Add<TableName>Row() method for the table containing the nullable DateTime column described above will take a DateTime? parameter.

Long ago, I asked about this issue on the MSDN forums, and ultimately the ADO project manager explained that nullable types were implemented at the same time as typed data sets, and his team didn't have time to fully integrate the two by .NET 2.0's ship date. And so far as I can tell, they haven't added new features to typed data sets since then.

Answer 6

It seems the Designer got the Database type for the column wrong.

Open up the xsd Designer, hit F4 to get the Properties Window open. Select the appropriate column and set Nullable (or something like that, don't remember the exact name) to true.