Problem InsertOnSubmit - Linq - ( class inherited from identity class )

Question

In the code below I got an instantiating problem using Linq

Context = using this method SetMappinImport , I got a sorted list cotaining the Column mapping between the columns of an external file and the members of the class "Artikel" which is inherited from the identity class "Bibliotheek" in the Datacontext (dbml )

When I ran the solution I got an instantiating problem which I couldn't understand ...

Somebody an idea why ? Thx in advance


my code :

 

public void SetMappinImport(DataSet ds, string tabelName, SortedList <string,string> mapping)

{

 

List<Artikel> artikelenImport = new List<Artikel>();

 

 

DataClass.LqDataContext db = new DataClass.LqDataContext();

 

switch

switch

 

(tabelName)

{

 

case "Bibliotheek":

 

foreach (DataRow rw in ds.Tables[0].Rows)

{

 

Artikel art = new Artikel();

 

int i = 1;

i = ds.Tables[0].Columns.IndexOf(mapping[

"Groep"]);

art.Groep =

Convert.ToString (rw[i]);

i = ds.Tables[0].Columns.IndexOf(mapping[

"Omschrijving"]);

art.Omschrijving =

Convert.ToString(rw[i]);

i = ds.Tables[0].Columns.IndexOf(mapping[

"PopCode"]);

art.PopCode =

Convert.ToString(rw[i]);

i = ds.Tables[0].Columns.IndexOf(mapping[

"Brutto"]);

art.Brutto =

Convert.ToString(rw[i]);

i = ds.Tables[0].Columns.IndexOf(mapping[

"Referentie"]);

art.Referentie =

Convert.ToString(rw[i]);

i = ds.Tables[0].Columns.IndexOf(mapping[

"Ve"]);

art.Ve =

Convert.ToString(rw[i]);

 

db.Bibliotheeks.InsertOnSubmit(art);    //<-Object reference not set to an instance of an object ????? art !=null & db.Bibliotheeks !=null

db.SubmitChanges();

artikelenImport.Add(art);

}

 

//db.Bibliotheeks.InsertAllOnSubmit(artikelenImport ); ---> List<Artikel> arts

 

 

break;

 

case "Productlijnen":

 

 

 

// to-do
break;

}

 

 

}

Answer 1

Hi bertoo,

 

This exception can be thrown when you use derived class from datacontext,

There are two workarounds for this issue,

1)    Use partial class.

http://stackoverflow.com/questions/499436/linq-insertonsubmit-nullreferenceexception

 

2)    Add additional properties

http://stackoverflow.com/questions/1572210/nullreferenceexception-when-calling-insertonsubmit-in-linq-to-sql

 

 

 

Does this work for you? If you have any questions or concerns, please update the thread and we will have a further discussion.

 

 

Best Regards

Yichun Feng

---

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Answer 2

Thank you for your usfull reply


an additional question :
Based on the first workaround ( partial class ) -> Am I right that I could create additional methods/fields to an inherited identity class from the datacontext?
Is this usefull ? or desired in a data layer for instance
Do you see practical circumstance where I should / could use the features / possibilities?


Best regards
bertoo 

Answer 3

Hi bertoo,

 

Since inherited class form datacontext will cause the problem you initially posted, I recommend that you just use partial class instead.

 

 

Best Regards

Yichun Feng

 

---

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