EF以外鍵Include() left join

項目中用EF實現外鍵查詢出的數據, 查詢數量正確, 但實現返回數據集數量不對

//DbContext.cs
HasRequired(s => s.ClassRoom)
            .WithMany()
            .HasForeignKey(student => student.ClassRoomId);

//查詢語句
dbRead.Set<Student>().Include(x=>x.ClassRoom);

查詢 .Count()和.ToList()結果數量不一致

經調試後發現生成的Sql語句爲 inner join

正確的結果應該是 left join

此時應該以下定義外鍵

HasOptional(s => s.ClassRoom)
             .WithMany()
             .HasForeignKey(student => student.ClassRoomId);

此時返回的結果就正確了!