如何在 C# 中使用 Linq to SQL 将匿名类型转换为列表 <dynamic>

Question

我是 C# 和 Linq 的新手。

实际上，我想将匿名类型返回到列表中。匿名类型包含 List、String 和 DateTime。我尝试使用下面的代码，但它给出了错误。请帮助并告诉我我缺少什么或建议我如何实现这一目标。

//错误：

System.InvalidCastException: Specified cast is not valid..

//编辑的 C# Linq 代码

        public List<AuditInfo> GetScanAudit(object Id, DateTime? fromTime, DateTime? toTime, string type = null,
            string user = null, Pager pager = null)
        {
            using (var ctx = new PlantDataContext())
            {
                var query = from audit in ctx.AuditLog
                            join ent in ctx.Scans on audit.RecordId equals ent.Id.ToString() into audits
                            from entaudits in audits.DefaultIfEmpty()
                            where audit.TypeFullName == "ABCD.DB.Model.Scan"
                            select new
                            {
                                audit,
                                entaudits
                            };

                if (Id != null)
                {
                    query = query.Where(x => x.audit.RecordId == Id.ToString());
                }
                if (fromTime.HasValue)
                {
                    var tmp = new DateTimeOffset(fromTime.Value.ToUniversalTime());
                    query = query.Where(x => x.audit.EventDateUTC >= tmp);
                }
                if (toTime.HasValue)
                {
                    var tmp = new DateTimeOffset(toTime.Value.ToUniversalTime());
                    query = query.Where(x => x.audit.EventDateUTC <= tmp);
                }
                if (!string.IsNullOrEmpty(type))
                {
                    var parseEvent = (EventType)Enum.Parse(typeof(EventType), type);
                    query = query.Where(x => x.audit.EventType == parseEvent);
                }
                if (!string.IsNullOrEmpty(user))
                {
                    query = query.Where(x => x.audit.UserName == user);
                }
                if (pager != null)
                {
                    var totalRecords = query.Count();
                    pager.TotalRecords = totalRecords;
                    var data = query.Select(x =>
                        new AuditInfo
                        {
                            x.audit.TypeFullName, //Here Error Occurs
                            x.audit.UserName,//Here Error Occurs
                            x.audit.EventType,//Here Error Occurs
                            x.audit.EventDateUTC,//Here Error Occurs
                            @LogDetails = x.audit.LogDetails.ToList(), //Here Error Occurs
                            x.entaudits.Name,
                            @Description = x.entaudits.Description
                        })
                        .OrderByDescending(x => x.EventDateUTC)
                        .Skip(pager.From)
                        .Take(pager.PageSize);
                    try
                    {
                        var list1 = data.ToList<AuditInfo>();
                    }
                    catch (Exception e)
                    {
                    }
                    var list = data.ToList<AuditInfo>();
                    pager.RecordCount = list.Count;
                    return list;
                }
                else
                {
                    var list = query.Select(x =>
                        new AuditInfo
                        {
                            x.audit.TypeFullName,
                            x.audit.UserName,
                            x.audit.EventType,
                            x.audit.EventDateUTC,
                            @LogDetails = x.audit.LogDetails.ToList(),
                            x.entaudits.Name,
                            @Description = x.entaudits.Description
                        })
                            .OrderByDescending(x => x.EventDateUTC)
                        .ToList<AuditInfo>();
                    return list;
                }
            }
        }

当我调试代码 totalRecords 变量显示计数 6，但显示异常消息时 Specified cast is not valid at this line var list1 = data.ToList();

Answer 1

您必须将匿名对象转换为动态对象。

要使用 linq 执行此操作，您可以使用 Cast<dynamic> linq 方法：

var list = query.Select(x =>
    new
    {
        x.audit.TypeFullName,
        x.audit.UserName,
        x.audit.EventType,
        x.audit.EventDateUTC,
        @LogDetails = x.audit.LogDetails.ToList(),
        x.entaudits.Name,
        @Description = x.entaudits.Description
    })
    .OrderByDescending(x => x.EventDateUTC)
    .AsEnumerable()
    .Cast<dynamic>()
    .ToList<dynamic>(); \\ here exception occures
return list;

Answer 2

您可以为您的方法使用强返回类型，例如 List<ClassName> 而不是 List<dynamic>

public List<ClassName> GetScanAudit(object Id, DateTime? fromTime, DateTime? toTime, string type = null, string user = null, Pager pager = null)
{
   ...
}

那么你的查询将是

var data = query.Select(x =>
                new ClassName
                {
                    TypeFullName = x.audit.TypeFullName,
                    UserName = x.audit.UserName,
                    EventType = x.audit.EventType,
                    EventDateUTC = x.audit.EventDateUTC,
                    LogDetails = x.audit.LogDetails.ToList(),
                    Name = x.entaudits.Name,
                    Description = x.entaudits.Description
                })
                .OrderByDescending(x => x.EventDateUTC)
                .Skip(pager.From)
                .Take(pager.PageSize);

var list = data.ToList<ClassName>();

你的强类型类看起来像

public class ClassName
{
    public string TypeFullName { get; set; }
    public string UserName { get; set; }
    public string EventType { get; set; }
    public DateTime EventDateUTC { get; set; }
    public List<LogDetail> LogDetails { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
}

确保每个属性的数据类型应与查询中的.Select 子句匹配

编辑：

if (pager != null)
            {
                var totalRecords = query.Count();
                pager.TotalRecords = totalRecords;
                var data = query.Select(x =>
                    new AuditInfo
                    {
                        TypeFullName = x.audit.TypeFullName,
                        UserName = x.audit.UserName,
                        EventType = x.audit.EventType,
                        EventDateUTC = x.audit.EventDateUTC,
                        LogDetails = x.audit.LogDetails.ToList(),
                        Name = x.entaudits.Name,
                        Description = x.entaudits.Description
                    })
                    .OrderByDescending(x => x.EventDateUTC)
                    .Skip(pager.From)
                    .Take(pager.PageSize);
                try
                {
                    var list1 = data.ToList<AuditInfo>();
                }
                catch (Exception e)
                {
                }
                var list = data.ToList<AuditInfo>();
                pager.RecordCount = list.Count;
                return list;
            }
            else
            {
                var list = query.Select(x =>
                    new AuditInfo
                    {
                        TypeFullName = x.audit.TypeFullName,
                        UserName = x.audit.UserName,
                        EventType = x.audit.EventType,
                        EventDateUTC = x.audit.EventDateUTC,
                        LogDetails = x.audit.LogDetails.ToList(),
                        Name = x.entaudits.Name,
                        Description = x.entaudits.Description
                    })
                        .OrderByDescending(x => x.EventDateUTC)
                    .ToList<AuditInfo>();
                return list;
            }