Error in linq query when finding average The null value cannot be assigned to a member with type System.Decimal which is a non-nullable value type.

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C#

dl_books.DataSource = (from st in obj.Book_details
                                      join d in obj.Rating_tables on st.Book_Id equals d.Book_id into pl
                                      where st.Category == "Health "
                                      orderby st.Book_Id descending


                                      select new { st.Book_Id , rat = pl.Average(c=>Convert.ToDecimal(c.Rating))  ,st.Price ,st.Name ,st.Image, }).Take(6);
               dl_books.DataBind();

this is my code and below is my error may be it is just bcz 4 some books i dnt having rates so then database is producing null and dts d problem any idea how to resolve this

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The null value cannot be assigned to a member with type System.Decimal which is a non-nullable value type.

Posted 19-Nov-13 0:22am

Omprakash Kukana

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JoCodes 19-Nov-13 7:02am

Try a null coalesce operator like Convert.ToDecimal(c.Rating??0)

Omprakash Kukana 20-Nov-13 2:23am

The null value cannot be assigned to a member with type System.Decimal which is a non-nullable value type.
this error is again m getting

JoCodes 20-Nov-13 2:32am

Rating is non nullable int type , right?

Omprakash Kukana 20-Nov-13 2:43am

yes

JoCodes 20-Nov-13 2:42am

Can you try (c => (Decimal?) c.Rating) instead of c=>Convert.ToDecimal(c.Rating) .. Check and let me know

Omprakash Kukana 20-Nov-13 2:46am

then can not convert type string to decimal

JoCodes 20-Nov-13 3:23am

Which is the string here? You are tryin to average the decimals/integers only right?

Omprakash Kukana 20-Nov-13 3:32am

yes rating is int type but i think c.rating is string type so i think problem is that for some books there is no any rating in database so that is returnig null value acc. me

JoCodes 20-Nov-13 3:37am

Instead of using string to handle null values make it nullable int or decimal

Omprakash Kukana 20-Nov-13 3:49am

is any other idea how to perform this code how to get average

JoCodes 20-Nov-13 4:07am

You need just average rating or need ratings based on something? any of the ways the datatype should be decimal only and need a groupby clause if you are calculating average rating of a book with some other parameter...

Omprakash Kukana 20-Nov-13 4:18am

http://www.codeproject.com/Questions/683760/error-in-linq-average-query
u can see here i hv to tables and want to find out average rating

JoCodes 20-Nov-13 4:13am

change the c.rating to nullable decimal , then your code will work...

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vinay.Singh · Answer 1 · 2013-11-20T19:58:00

Hi try this one

C#

dl_books.DataSource = (from st in obj.Book_details
                                      join d in obj.Rating_tables on st.Book_Id equals d.Book_id into pl
                                      where st.Category == "Health "
                                      orderby st.Book_Id descending
 

                                      select new { st.Book_Id , rat = pl.Average(c=>(decimal)c.Rating)  ,st.Price ,st.Name ,st.Image, }).Take(6);
               dl_books.DataBind();