Can the FileHelpers library write classes containing nullable fields as well as read them?

问题

I'm using version 2.0 of the FileHelpers library which is documented as being able to handle .NET 2.0 Nullable types.

I'm using the code given in the example from the documentation:

[DelimitedRecord("|")]   
public class Orders   
{   
    public int OrderID;   

    public DateTime? OrderDate;   

    [FieldConverter(ConverterKind.Date, "ddMMyyyy")]     
    public DateTime? RequiredDate;   

    public int? ShipVia;   
}

With a FileHelperEngine I can successfully read in a file which has no value for the OrderDate, RequiredDate or ShipVia fields. The file looks like:

1|||

However, I cannot then write out the resulting Orders[] to file - the library throws a NullReferenceException, stack trace below:

at FileHelpers.ConvertHelpers.CultureConverter.FieldToString(Object from) at FileHelpers.FieldBase.BaseFieldString(Object fieldValue) at FileHelpers.DelimitedField.CreateFieldString(StringBuilder sb, Object fieldValue) at FileHelpers.FieldBase.AssignToString(StringBuilder sb, Object fieldValue) at FileHelpers.RecordInfo.RecordToString(Object record) at FileHelpers.FileHelperEngine1.WriteStream(TextWriter writer, IEnumerable1 records, Int32 maxRecords) at FileHelpers.FileHelperEngine1.WriteFile(String fileName, IEnumerable1 records, Int32 maxRecords) at FileHelpers.FileHelperEngine1.WriteFile(String fileName, IEnumerable1 records) at TestingFileHelpers.Program.Main(String[] args) in C:\dev\src\TestingFileHelpers\TestingFileHelpers\Program.cs:line 19 at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args) at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ThreadHelper.ThreadStart_Context(Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart()

I'm sure I must be missing something here but I cannot figure out what it is. Any help much appreciated.

回答1:

Can you try with the last version of the library:

http://teamcity.codebetter.com/viewLog.html?buildId=21768&tab=artifacts&buildTypeId=bt65 (login as guest)

If that version dot fix the error just tell me in a comment and I will add a test case to the lib to ensure it works

回答2:

Use the [FieldNullValue("")] attribute to specify default values for the empty fields.

来源：https://stackoverflow.com/questions/5066255/can-the-filehelpers-library-write-classes-containing-nullable-fields-as-well-as

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filehelpers