Json 序列化错误“已经有一个打开的 DataReader 与此命令关联”

Question

Json 序列化命令给出了这个错误。我使用Newtonsoft.Json 来避免序列化时的循环引用错误。

private IQueryable<Study> GetStudiesData()
{
    var currUser = UserManager.FindById(User.Identity.GetUserId());
    var currUserRole = currUser.Roles.First();

    IQueryable<Study> studies;
    if (User.IsInRole("SuperAdmin")) {
        studies = db.Studies; //all studies from all centers 
    }
    else {
        var assignedStudies = db.Studies.Where(s => s.AssignedUserID == currUser.Id);

        studies = db.Studies.Where(s => s.User.CenterId == currUser.CenterId && s.RoleID == currUserRole.RoleId)
            .Concat(assignedStudies);
    }

    return studies;
}

//ajax call to this function gives error
public ActionResult GetStudies(int pageSize = 10, int pageNum = 1)
{
    var studies = GetStudiesData();
    var studiesCount = studies.Count();
    var studiesPaged = studies.OrderBy(s=>s.PatientID).Skip(pageSize*pageNum).Take(pageSize);

    var result = new { TotalRows = studiesCount, Rows = studiesPaged };

    //this line gives error
    //There is already an open DataReader associated with this Command which must be closed first.
    var data = Newtonsoft.Json.JsonConvert.SerializeObject(result, Newtonsoft.Json.Formatting.None,
    new Newtonsoft.Json.JsonSerializerSettings()
    {
        ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
    });

    return Json(data, JsonRequestBehavior.AllowGet);
}

我在var data = Newtonsoft.Json.JsonConvert.SerializeObject(result, ...) 中尝试了result = studies、result = studiesPaged、result = studiesCount。 只有studiesPaged 给出了错误。

我可以使用MultipleActiveResultSets=True; 解决它，但我在哪里进行第二个查询？

更新

public ActionResult GetStudies(int pageSize = 10, int pageNum = 1) { var 研究 = GetStudiesData().ToList(); //已解决，创建了另一个问题 //其他代码 }

现在返回的 Json 看起来像是再次将 Json 序列化为字符串。

"{\"TotalRows\":5,\"Rows\":[{\"AssignedUser\":null, ..... }]}"

当被 javascript 解析时，它被分割成一个字符数组。

更新2

改变了

//data is a json string after serialization
return Json(data, JsonRequestBehavior.AllowGet); //Serializing the Json

到

return Content(data, "application/json");

Answer 1

将它分配给一个列表，然后查询它应该可以防止这种情况：

public ActionResult GetStudies(int pageSize = 10, int pageNum = 1)
{
    var studies = GetStudiesData().ToList();
    var studiesCount = studies.Count();
    var studiesPaged = studies.OrderBy(s=>s.PatientID).Skip(pageSize*pageNum).Take(pageSize);

    var result = new { TotalRows = studiesCount, Rows = studiesPaged };

    //this line gives error
    //There is already an open DataReader associated with this Command which must be closed first.
    var data = Newtonsoft.Json.JsonConvert.SerializeObject(result, Newtonsoft.Json.Formatting.None,
    new Newtonsoft.Json.JsonSerializerSettings()
    {
        ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
    });

    return Json(data, JsonRequestBehavior.AllowGet);
}

Answer 2

var assignedStudies = db.Studies.Where(s => s.AssignedUserID == currUser.Id);

studies = db.Studies.Where(s => s.User.CenterId == currUser.CenterId && 
              s.RoleID == currUserRole.RoleId).Concat(assignedStudies);

您对DbSet<Studies> 有两个查询