LINQ to Entities 不识别方法"System.String ToString()"该怎么解决

LINQ to Entities 不识别方法"System.String ToString()"

var query = from a in context.Users

                           from b in context.Companies

                           from c in context.Accounts

                           where a.Id == c.CreateUser && c.CompanyId == b.Id && c.AllPassState == false

                         select new WaitAuditEntity

                           {

                               Id = c.Id,

                               AccountName = c.AccountName,

                               ContactName = c.ContactName,

                               CompanyName = b.CompanyName,

                               OpenCompany = a.BelongsCompany,

                               Mobile = c.Mobile,

                               AccountState = c.AccountState,

                               PaymentState = c.PaymentState,

                               ReviewState = c.ReviewState,

                               EstablishState = c.EstablishState,

                               AllPassState = c.AllPassState,

                               CreateTime = c.CreateTime.ToString(),

                               UpdateTime = c.UpdateTime.ToString(),

                               CreateUserName = a.Name                              

                           };

这里的 CreateTime = c.CreateTime.ToString(),
                               UpdateTime = c.UpdateTime.ToString(),会在执行时报错LINQ to Entities 不识别方法"System.String ToString()"。请问该怎么写？
------解决思路----------------------
var query = (from a in context.Users
                           from b in context.Companies
                           from c in context.Accounts
                           where a.Id == c.CreateUser && c.CompanyId == b.Id && c.AllPassState == false
                         select new WaitAuditEntity
                           {
                              a,b,c                       
                           }).ToList().select(x=>new{
                           //这里写一次
                           });
------解决思路----------------------
                          var query = from a in context.Users
                           from b in context.Companies
                           from c in context.Accounts
                           let _CreateTime c.CreateTime.ToString(), _UpdateTime = c.UpdateTime.ToString()
                           where a.Id == c.CreateUser && c.CompanyId == b.Id && c.AllPassState == false
                         select new WaitAuditEntity
                           {
                               Id = c.Id,
                               AccountName = c.AccountName,
                               ContactName = c.ContactName,
                               CompanyName = b.CompanyName,
                               OpenCompany = a.BelongsCompany,
                               Mobile = c.Mobile,
                               AccountState = c.AccountState,
                               PaymentState = c.PaymentState,
                               ReviewState = c.ReviewState,
                               EstablishState = c.EstablishState,
                               AllPassState = c.AllPassState,
                               CreateTime = _CreateTime ,
                               UpdateTime = _UpdateTime ,
                               CreateUserName = a.Name                              
                           };