c# - EF 联盟问题“无法从

Question

这应该是一个简单的联合查询，但即使操作类型相同，它也会抛出一个错误:

Instance argument: cannot convert from System.Linq.IQueryable<AnonymousType#1> to System.Linq.ParallelQuery<AnonymousType#2>

如果我删除此列，则它工作正常。在第一次选择中，我想将操作值分配给“0”。任何帮助表示赞赏。谢谢

(from p in Pages join pa in PageAct on p.PageId equals pa.PageId
 select new
 {
     PageId = p.PageId,
     PgName = p.PgName,
     ActionId = pa.ActionId,
     ActionName = pa.ActionName,
     **action = 0**
 }).Union(from p in Pages
 join pa in PageAct on p.PageId equals pa.PageId
 join rp in RolePerm on pa.ActionId equals rp.ActionId into jrs
 from jrResult in jrs.DefaultIfEmpty()
 where jrResult.RoleId == 1
 select new
 {
     PageId = p.PageId,
     PgName = p.PgName,
     ActionId = pa.ActionId,
     ActionName = pa.ActionName,
     action = jrResult.ActionId
 })

Answer 1

匿名对象应具有完全相同的签名才能被视为相同。

如果 RolePerm.ActionId 是可空类型，则第一个匿名对象属性类型也应该是可空的。实际类型也可以是不可空的，但由于这是左连接，您不应忘记显式转换为可空 int，否则您可能会遇到运行时异常。

(from p in Pages join pa in PageAct on p.PageId equals pa.PageId
 select new
 {
     PageId = p.PageId,
     PgName = p.PgName,
     ActionId = pa.ActionId,
     ActionName = pa.ActionName,
     action = (int?)0
 }).Union(from p in Pages
 join pa in PageAct on p.PageId equals pa.PageId
 join rp in RolePerm on pa.ActionId equals rp.ActionId into jrs
 from jrResult in jrs.DefaultIfEmpty()
 where jrResult.RoleId == 1
 select new
 {
     PageId = p.PageId,
     PgName = p.PgName,
     ActionId = pa.ActionId,
     ActionName = pa.ActionName,
     action = (int?)jrResult.ActionId // should cast, even if ActionId is not nullable
                                      // because left join might give null
 })