从联接linq语句中选择视图模型列表

本文关键字：选择 视图 模型 列表 语句 linq | 更新日期: 2023-09-27 18:08:45

我在linq语句中有一个简单的连接

var events = (from e in context.Events
join o in context.Offices on e.OfficeId equals o.Id
where e.StartDate >= DateTime.Now
select e)
.AsEnumerable()
.Select(x => new vm_Events()
{
    Cost = x.Cost,
    StartDate = x.StartDate,
    EndDate = x.EndDate.HasValue ? (x.EndDate).Value : new DateTime(),
    Address = x.Address,
    Image = x.SupportingImage,
    Info = x.Info,
    Name = x.Name,
    LocationName = x.LocationName,
    Office =
        string.Format("For more information please call the {0} office at {1}", x.Offices.Name,
            x.Offices.PhoneNumber),
    StateZip = string.Format("{0}, {1}, {2}", x.City, x.State, x.Zip)
}).ToList();

查询构建得很好，但是当我包含连接的offices表时，给了我空引用。在呼叫.AsEnumerable()之前，我是否需要将select e更改为其他内容?

我已经验证了我在office表上查找的数据不为空

从联接linq语句中选择视图模型列表

如果没有延迟加载，则无法在AsEnumerable之后访问x.Offices.Name。我建议你分两步:

  1. 在匿名类中加载所有需要的数据
    2. 构建vm_Events对象
var events = (from e in context.Events
join o in context.Offices on e.OfficeId equals o.Id
where e.StartDate >= DateTime.Now
select e)
.Select(x => new
{
    Cost = x.Cost,
    StartDate = x.StartDate,
    EndDate = x.EndDate.HasValue ? (x.EndDate).Value : new DateTime(),
    Address = x.Address,
    Image = x.SupportingImage,
    Info = x.Info,
    Name = x.Name,
    LocationName = x.LocationName,
    OfficeName = x.Offices.Name,
    OfficePhoneNumber = x.Offices.PhoneNumber,
    x.City,
    x.State, 
    x.Zip
}).ToList()
.Select(x=> new vm_Events
{
    Cost = x.Cost,
    StartDate = x.StartDate,
    EndDate = x.EndDate,
    Address = x.Address,
    Image = x.SupportingImage,
    Info = x.Info,
    Name = x.Name,
    LocationName = x.LocationName,
    Office = string.Format("For more information please call the {0} office at {1}", x.OfficeName, x.OfficePhoneNumber),
    StateZip = string.Format("{0}, {1}, {2}", x.City, x.State, x.Zip)
}).ToList();
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