Invalidoperationexception：已经有一个与此命令关联的打开的datareader，必须先关闭它。使用ASP.NET身份 [英] Invalidoperationexception: there is already an open datareader associated with this command which must be closed first. With ASP.NET identity

问题描述

我正在尝试从数据库返回数据：

I'm trying to return data from database:

public List<DataModel> GET()
    {
        foreach (var users in db.Users) {
            var user = db.Users.Select(x => new DataModel()
            {
                Email = users.Email,
                UserName = users.UserName,
                FirstName = users.FirstName,
                LastName = users.LastName,
                Age = users.Age,
                Phone = users.Phone,
                Department = users.Department
            });
            return user.ToList();

        }

这是db class：

Here is db class:

public class ApplicationDbContext : IdentityDbContext<ApplicationUser, CustomRole,
int, CustomUserLogin, CustomUserRole, CustomUserClaim>
{
    public ApplicationDbContext()
        : base("DefaultConnection")
    {
    }

    public static ApplicationDbContext Create()
    {
        return new ApplicationDbContext();
    }
}

这是错误：

Here is the error:

InvalidOperationException: There is already an open DataReader associated with this Command which must be closed first.

你能告诉我这段代码有什么问题吗？



我尝试了什么：



我在数据库中有四条记录，以下代码返回四条记录但是有第一条记录数据!!

Could you please tell what's wrong with this code?

What I have tried:

I have four record in database and the following code return four record but with first record data !!

public List<DataModel> GET()
           {


                   var user = db.Users.Select(x => new DataModel()
                   {
                       Email = db.Users.FirstOrDefault().Email,
                       UserName = db.Users.FirstOrDefault().UserName,
                       FirstName = db.Users.FirstOrDefault().FirstName,
                       LastName = db.Users.FirstOrDefault().LastName,
                       Age = db.Users.FirstOrDefault().Age,
                       Phone = db.Users.FirstOrDefault().Phone,
                       Department = db.Users.FirstOrDefault().Department
                   });
                   return user.ToList();

           }

推荐答案

这可能是因为这行

It's probably because this line

foreach (var users in db.Users)

打开一个连接，这一行

opens a connection and this line

var user = db.Users.Select(

设置第二个连接，当你在下一行使用.ToList时激活它。



你实际上不需要这两个循环，这是未经测试但尝试类似

sets up a second connection which is activated when you use .ToList on the following line.

You don't actually need the two loops, this is untested but try something like

public List<DataModel> GET()
    {
            var user = db.Users.Select(x => new DataModel()
            {
                Email = x.Email,
                UserName = x.UserName,
                FirstName = x.FirstName,
                LastName = x.LastName,
                Age = x.Age,
                Phone = x.Phone,
                Department = x.Department
            });

            return user.ToList();

        }

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