SqlException 因为子查询返回超过 1 个值

我有以下 LINQ 查询，用于构造一个结构以填充到 JavaScript 网格库中，这与本示例无关，但我想我仍然会解释这一点。

var output = myObjects.Select(
    p => new RowModel
    {
         ID = p.LeadUID,
         Cells =
             new CellCollection(fields,
                p.myDataDatas.Where(q => q.myField.ParentUID == null).Select(
                    q => new CellModel
                             {
                                 Value = q.Value,
                                 Name = q.myField.Description,
                                 Display = q.myField.Description
                             }).ToList()
                ,
                new CellModel
                    {
                        Name = "Campaign",
                        Display = "Campaign",
                        Value = p.Campaign.Name
                    }
                ,
                new CellModel
                    {
                        Name = "CampaignEnabled",
                        Display = "CampaignEnabled",
                        Value = p.Campaign.IsActive.ToString()
                    },
                new CellModel
                    {
                        Name = "Date Received",
                        Display = "Date Received",
                        Value = p.DateAdded.ToString()
                    }
                ,
                new CellModel
                    {
                        Name = "Is Valid",
                        Display = "Is Valid",
                        Value = BooleanMap[p.IsValid]
                    }
                ,
                new CellModel
                    {
                        Name = "Invalid Reason",
                        Display = "Invalid Reason",
                        Value = p.InvalidReason

                    }
                ,
                new CellModel
                    {
                        Name = "Is Returned",
                        Display = "Is Returned",
                        Value = BooleanMap[p.IsReturned]
                    }
                ,
                new CellModel
                    {
                        Name = "Return Reason",
                        Display = "Return Reason",
                        Value =
                            context.MYReturns.SingleOrDefault(
                                l => l.LeadUID == p.MyUID).ReturnReason
                    }
                ,
                new CellModel
                    {
                        Name = "Workflow",
                        Display = "Workflow",
                        Value =
                            context.Stages.SingleOrDefault(
                                s => s.LifecycleStageUID == p.LifecycleStageUID).
                            Name
                    }
                ,
                new CellModel
                    {
                        Name = "WorkflowEnabled",
                        Display = "WorkflowEnabled",
                        Value =
                            context.Stages.SingleOrDefault(
                                s => s.LifecycleStageUID == p.LifecycleStageUID).
                            IsActive.ToString()
                    }
                ,
                new CellModel
                    {
                        Name = "Status",
                        Display = "Status",
                        Value = p.MyStatus.Name
                    }
                ,
                new CellModel
                    {
                        Name = "StatusDeleted",
                        Display = "StatusDeleted",
                        Value = (p.MyStatus.Deleted).ToString()
                    }
                ,
                new CellModel
                    {
                        Name = "LeadSource",
                        Display = "Lead Source",
                        Value = MySourcesMap[p.AccountSourceUID].Name
                    }
                ,
                new CellModel
                    {
                        Name = "LeadSourceEnabled",
                        Display = "LeadSourceEnabled",
                        Value = AccountSoucesEnabledMap[p.AccountSourceUID].ToString()
                    }
                        )
                     }
            );
            var rows = output.ToList();
            return rows;

我希望更改代码中大多数变量的名称不会影响整体情况。

我面临的问题是有时我得到以下信息SQLException信息：

子查询返回超过 1 个值。当子查询跟随时这是不允许的=, !=, <, <= , >, >=或者当子查询用作表达式时。

我想知道的是，在我的查询中，我在哪里做错了一些有时（大多数时候）会起作用的事情，然后很少返回此错误消息。如何正确预防这种情况的发生？

use the 数据上下文.日志 http://msdn.microsoft.com/en-us/library/system.data.linq.datacontext.log.aspx属性来显示查询生成的 sql。当只有一个结果有效时，您很可能有一个子查询生成多个结果。例如，如果子查询中返回多个结果，则以下 SQL 将失败：

Select * from orders where customer_id = 
  (select customer_id from customer where name ='bob')

如果子查询返回多个结果，则主查询中的 where 子句的相等性就没有意义。

您可能需要更改存储中某些数据列的唯一性，以确保子查询中只返回一行。另一种选择是更改您的类，以便分配给的特定问题属性是一个集合而不是单个值。