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How could I write to a file a dynamic object using FileHelpers?

I'm actually pursuing a way to create csv file which records could vary on type and order. They are defined by the user on both ways and I'm actually handling their types safely.
I loved using FileHelpers library in order to read/write files on C# since it's fast, reliable and trustable, so I was wondering how could I perform this export operation using it, and reviewing questions like this one the evil part comes when needing to populate the class with the desired values, so I could write the file. All the related questions are focusing on reading registries and I need to write them.
Am I right thinking that I might need to use Reflection so I could roam this new type and its properties or is there any way to "add a record" specifying the value while creating the fields?
This FileHelpers way was an option and of course the second one was doing this manually, but I was curious if there is an easier way.
var builder = new DelimitedClassBuilder("DynamicDocument", ";");
builder.AddField("Date", typeof(DateTime));
var dynamicType = builder.CreateRecordClass();
//...

Using the class builders is the best way to do this with FileHelpers. You do need to keep a copy of the type that is created so it can be used by your generic classes.
Just remember, that you must do all the work before calling CreateRecordClass() as that then generates the type.
Here is a link to another S/O question with a whole bunch of code that shows how to do it: FileHelpers.Dynamic.ClassBuilder.CreateRecordClass Error
Now, if you are working purely with properly formatted files, you can let FileHelpers do all that work for you as long as they are always properly delimited and you handle any type conversion based on the column name.

Cant use DataTable.New

Im trying to read a csv file using CSVTools library the code that I have to use to get the csv file in to a data table is,
var dt = DataTable.New.ReadLazy(filename);
But the problem is there is no ".New" keyword. When I write DataTable.New it shows an error. Can someone help me ?

You need to include using statement on top of c# file as below
using DataAccess;
or use
var dt = DataAccess.DataTable.New.ReadLazy(filename);

Which means the DataTable that you are using is not belongs to the
expected namespace, use fully qualified name to get the correct
class.
You may have both using DataAccess; as well as System.Data in your using section, so by declaring DataTable alone will made compiler to assumes that it belongs to System.Data. By specifying the DataTable as DataAccess.DataTable you can help the compiler to find the exact class that you are looking for. This kind of specification is called fully qualified names. Make use of them and come out from that specified error. Your declaration will be like the following:
var dt = DataAccess.DataTable.New.ReadLazy(filename);

Merging Objects of different types

I have two objects (WS.Customer and EF.Customer). The reason for this is my vendor didn't expose all of the fields in their object (WS.Customer) and I need to insert and update into those fields.
I need to merge WS.Customer -> EF.Customer and later merge EF.Customer -> WS.Customer. EF.Customer will have some extra fields that WS.Customer won't have, but when the field names match - I want the values merged.
I also only want to merge values where the destination field is null, empty, or a default value in case of a Guid.
I know I could use to Linq to query each object and build the other, but is there a less verbose way of doing things? I have some other objects I need to use this approach for and don't feel like spending a weeks typing away.
Thanks

You can use one of the available object-to-object mappers library like AutoMapper or EmitMapper. They will take care of copying the data in both directions and skip fields if properly configured. For example with EmitMapper your code might look like this:
ObjectMapperManager.DefaultInstance
.GetMapper<WS.Customer, EF.Customer>(<your configuration object here>)
.Map(customerSource, customerDestination);

What do you mean by "merged"? I guess you need to "translate" from one instance to another, i.e. copy values when name and type of property matches. Please have a look at the implementation provided in ServiceStack, the extension method of object - TranslateTo method: https://github.com/ServiceStack/ServiceStack/blob/master/src/ServiceStack.Common/ReflectionExtensions.cs#L31

Why dataTable Name is necessary to be given in webServices

I wondering why it throws a error whenever i not intended to give name of datable.As we know there are constructor for datable class is overloaded.so If i using parameter less constructor is give the error by the basis of serialization .
Can Someone Explain Me why to use Parametrized one but not default for DataTable .

It's because the name is required for the data table to serialize properly.
Why is this? Well, the exact reason seems to be that the serialization process uses the table name as a key, and specifically, an empty data set is created to import it back in. When the name is not present, the part that looks for the table name throws an exception and this is why you see the error you are getting.
You don't have to use the constructor, though, you can set the TableName outside:
DataTable myTable = new DataTable();
myTable.TableName = "PleaseDontKillMySerialization";
If you are interested, you can look at the contents of the class using ILSpy. This way you can see for yourself how the class is created and look at how serialization works for this class.
As Marc mentions, though, using DataTable restricts you to .Net clients only. It's also quite a large object when serialized so more data has to be transferred per request.

Specifying SqlString length for a CLR stored procedure

I'm writing stored procedures in C# at the moment and I've run into a problem with the size of a parameter.
So I've created a project in VS 2008 and created several stored procedures which all look a bit like this:
public partial class StoredProcedures
{
[Microsoft.SqlServer.Server.SqlProcedure]
public static void SaveProgress(... SqlString logpart, ...)
{
...stuff...
}
}
Now because I've not specified anything else, when I deploy this to a database, the CREATE DATABASE statement (apparently) gets created with a nvarchar(4000) as the definition for the input parameter.
However, I regularly have to flush log parts larger than 4000 chars, so I'd like that to be nvarchar(MAX).
Now I think I can do some jiggery-pokery and use Management Studio to re-define the CREATE DATABASE statment, but I'd actually like to define the fact that I want it to be MAX in the project/solution, so the deployment gets done correctly and I don't have to start adding large wads of comments and/or documentation for anyone who needs to maintain this code after me.
Is there any way to specify this in the code or maybe in the AssemblyInfo or something like that?

Revisiting this years later, I tried to use SqlChars in a function that read data from the database and returned a formatted string with data in it. Using SqlChars actually made the function bomb, stating that it could not find linked server System - an error message that seems to have nothing to do with the problem, as I was never referencing a linked server in the first place.
Changing the return type and parameters back to SqlString, adding [return:SqlFacet(MaxSize = -1)] attribute to the function, and adding [SqlFacet(MaxSize = -1)] to each parameter made my function work properly.

Try using SqlChars. SqlChars automatically maps to NVARCHAR(MAX)