'可为空的 object 必须有一个值。' 对于列表 LINQ c#

Question

In database I have next model tblWorkItem with next field:

public List<xWorkItemItemFailReason> WorkItemItemFailReasons { get; set; }

When I am trying to get tblWorkItem data from database

_db.tblWorkItem.Where(x=>x.WorkItemItemFailReasons != null)

I have next error

System.InvalidOperationException: 'Nullable object must have a value.'

How I can check if this field is not null?

Answer 1

Problem in xWorkItemItemFailReason class. It has some property of primitive type ( int , long , ...) that is not nullable, but has no value in database table. Check them.

Answer 2

In your modal class have some not nullable field so when fetching from database it comes with null values. so make it nullable . public int? FieldName {Get;set;}

Answer 3

if its .net core 3.0 or earlier there is a known issue where

Simple query filter breaks simple projection https://github.com/dotnet/efcore/issues/13517

Answer 4

You should also make sure there are no data integrity problems with your foreign key relationships. A foreign key value in the parent table that doesn't exist in the child table will throw this exception too (eg, you set the foreign key to 0 instead of null if there's no child, and no child record in the database has a key value of 0).