.NET 6迁移时Dynamic LINQ报“Nullable object must have a value”错误求助

原.NET Core 3.1可运行代码 #

query = query.GroupJoin(ParsingConfig.DefaultEFCore21,
                        detailObject,
                        "new { it.ExternalDataId2.Value AS I0}",
                        "new { Id AS I0}",
                        "new (outer AS A, inner AS B)");

query = query.SelectMany("B.DefaultIfEmpty()",
                         "new { source.A.Id AS Id,source.A.ExternalDataId2 AS ExternalDataId2,detail.Title AS ExternalData2Ref_Title,detail.Id AS ExternalData2Ref_Id}",
                         "source",
                         "detail");

query.ToDynamicListAsync();

迁移至.NET 6后的错误 #

异常提示：

Nullable object must have a value.

完整异常堆栈：

Message: 
Test method FrameworkTests.DataLayer.FindTests.FindValueExternal threw exception: 
NTSFramework.DataLayer.DataLayerException: Errore generico di repository Nullable object must have a value.
 ---> System.InvalidOperationException: Nullable object must have a value.

  Stack Trace: 
lambda_method559(Closure , QueryContext , DbDataReader , ResultContext , SingleQueryResultCoordinator )
AsyncEnumerator.MoveNextAsync()
DynamicEnumerableAsyncExtensions.ToListAsync[T](IEnumerable source, CancellationToken cancellationToken)
DynamicEnumerableAsyncExtensions.ToListAsync[T](IEnumerable source, CancellationToken cancellationToken)
BaseDataLayer.FindValuesAsync[TModel](FindValuesOptions findOptions) line 866

注：通过SQL Profiler可见查询已执行，移除ParsingConfig无法解决问题。

尝试过的修改（可运行但无法得到所需结果） #

query = query.SelectMany("B.DefaultIfEmpty()",
                         "new { source.A.Id AS Id,source.A.ExternalDataId2 AS ExternalDataId2,detail As ExternalData2Ref}",
                         "source",
                         "detail");

解决方案 #

问题原因 #

.NET 6对Nullable类型的检查和EF Core的结果映射逻辑更严格。由于使用DefaultIfEmpty()实现左连接，当detail（即B表无匹配数据）为null时，直接访问detail.Title或detail.Id会触发异常——如果这些属性是非Nullable值类型（如int），EF Core 6不允许将null映射到非Nullable字段，而.NET Core 3.1可能默认忽略了这个检查。

修改后的代码 #

在SelectMany的投影表达式中，为detail的属性添加空值判断：

query = query.SelectMany("B.DefaultIfEmpty()",
                         "new { source.A.Id AS Id,source.A.ExternalDataId2 AS ExternalDataId2,detail == null ? null : detail.Title AS ExternalData2Ref_Title,detail == null ? null : detail.Id AS ExternalData2Ref_Id}",
                         "source",
                         "detail");

说明 #

• 通过detail == null ? null : detail.XXX的三元判断，确保当detail为null时返回null，而非强制访问非Nullable属性。
• 如果detail.Id是值类型（如int），需要确保目标模型中对应的ExternalData2Ref_Id字段是可空类型（如int?），否则仍会出现映射错误。

内容的提问来源于stack exchange，提问作者Paolo Crociati