如何加载IEnumerable类型的相关实体?

我试图加载一个SingleOrDefault实体的相关实体，但我得到以下例外:

IEnumerable类型的navigation属性不是iccollection类型的单个实现

我已经尝试了几种方法，最终对上下文的每个查询都得到了上面相同的错误(我在注释中包含了其他方法)。

using(var context = CustomObjectContextCreator.Create())
        {
            return  context.Job.Include("Surveys").Include("SiteInfoes")
        .Where(r => r.Jobid == jobId).SingleOrDefault();
            //context.ContextOptions.LazyLoadingEnabled = false;
            //var Job = context.Job.Where(r => r.Jobid == jobId).SingleOrDefault();
            //context.LoadProperty(Job, "Surveys");
            //context.LoadProperty(Job, "SiteInfoes");
            //var Job = (from j in context.Job
            //                   .Include("Surveys")
            //                   .Include("SiteInfoes")
            //               select j).SingleOrDefault();
            //var Job = context.Job.Where(r => r.Jobid == jobId).SingleOrDefault();
            //var surveys = context.Surveys.Where(s => s.JobID == jobId);
            //var wellInfoes = context.SiteInfoes.Where(w => w.Jobid == jobId);
            //Job.Surveys = surveys.ToList();
            //Job.SiteInfoes = wellInfoes.ToList();
            //return Job;
        }

以下是我使用的POCO对象:

    public class Job
    {
        public int? Jobid { get; set; }
        public string JobLocation { get; set; }
        public string JobName { get; set; }
        public virtual IEnumerable<Survey> Surveys { get; set; }
        public virtual IEnumerable<SiteInfo> SiteInfoes { get; set; }
    }
public class Survey
    {
        public int SurveyID { get; set; }
        public int? JobID { get; set; }
        public DateTime? DateTime { get; set; }
        public string Report { get; set; }
        public virtual Job Job { get; set; }
    }
public class SiteInfo
    {
      public int Jobid { get; set; }
      public string SiteLocation { get; set; }
      public virtual JobInfo JobInfo { get; set; }
    }

如何正确加载相关实体?