The cast to value type 'Int32' failed because the materializ

nave

13y16k.NET

I have this code:

var item = (from se in _db.Events
where se.ID == id
select new PseudoEvent()
{
ID = se.ID,
categoryId = se.Categories.ID,
}).FirstOrDefault();

The "Events" and "Categories" tables have a relationship:
"Events" table > Category_ID = "Categories" table > ID

When i dont select a category for the event the "Category_ID" in the "Events" table stays "NULL" and in my code above i get this error:

The cast to value type 'Int32' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type

How can i fix that so the event item will be shown even if the Category_ID column is null?

Please advise
Thanks

2 Replies

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Sanjeeb Lenka13y ago
Accepted answer
try this:

var item = (from se in _db.Events
where se.ID == id
select new PseudoEvent()
{
ID = se.ID,
categoryId = (se.CategoriesID== null) ? 0 : se.CategoriesID };
}).FirstOrDefault();

here if catagoryid come as null it will assign 0 to it.
0
nave13y ago
Thanks! this works

I have another question related to this issue:
How do i update the Category_ID column back to null?

On insert or update i use this:

getCategory = _db.Categories.Find(id);
Events.Categories = getCategory; //add foreign key

But if the category is 0 (not selected) i want to update the relationship Category_ID back to null.

Try to do it like that:

Events.Categories = null; //add foreign key

But it doesn't seems to work

Please advise
Thanks
0