Entity Framework，已经有一个打开的 DataReader 与此连接关联，必须先将其关闭

Question

在"each"中，当运行时"FirstOrDefault"会报错"There is already an open DataReader associated with this Connection which must be closed first."。怎么办？

public int SetUser(string[] dIds, string pId)
{
    using (var scope = _dbContextScopeFactory.Create())
    {
        var db = scope.DbContexts.Get<JuCheapContext>();

        var users = db.Users;

        var user = users.FirstOrDefault(m => m.Id == pId);
        if (user.Places == null)
        {
            user.Places = new List<PlaceEntity>();
        }

        var place = db.Place.Include(m => m.User).Where(m => dIds.Contains(m.Id));

        place.Each(m =>
        {
            user.Places.Add(m);

            //There is already an open DataReader associated with this Connection which must be closed first.
            var pu = users.FirstOrDefault(u => u.LoginName == m.Key);

            if (pu != null)
            {
                pu.FId = pId;
            }

        });

        return db.SaveChanges();
    }
}

Answer 1

当你说

place.Each(m =>

您正在使用 reader 迭代数据库中的项目

然后

  var pu = users.FirstOrDefault(u => u.LoginName == m.Key);

第二个reader在第一个还在执行的时候进入，出现错误

调用ToList()将数据存入内存并关闭reader

var place = db.Place.Include(m => m.User).Where(m => dIds.Contains(m.Id)).ToList();

您还可以启用 MARS（多个活动结果集）

https://msdn.microsoft.com/en-us/library/h32h3abf(v=vs.110).aspx

Entity Framework，已经有一个打开的 DataReader 与此连接关联，必须先将其关闭

Entity Framework,There is already an open DataReader associated with this Connection which must be closed first

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datareader