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我有以下 Linq/Lambda 表达式将COMMENTS和ATTACHMENTS关联到RECORDS（这些是数据库中表的名称）。

var comments = repositoryBase.Query<Comments>()
    .Select(x => x);

var attachments = repositoryBase.Query<Attachment>()
    .Where(x => x.DeletedFlag == false)
    .Select(x => x);

var recordItems = repositoryBase.Query<Record>()
    .Where(x => x.DepartmentId == departmentIdId && x.DeletedFlag == false);

recordItems = recordItems
    .Where(x => x.Featured == true && (x.PhaseTypeId == 2 || x.PhaseTypeId == 3));  // filtering

var recordComments = recordItems
    .GroupJoin(comments,
        itm => new { a = 1, b = itm.RecordId },
        c => new { a = c.TypeId, b = c.Id },
        (itm, c) => new { c, itm })
    .SelectMany(x => x.c.DefaultIfEmpty(), (x, y) => new
    {
        Comments = (y != null) ? true : false,
        CommentsCount = x.c.Count(),
        RecordId = x.itm.RecordId,
        Featured = x.itm.Featured,
        Id = x.itm.RecordId,
        PhaseName = x.itm.PhaseType.PhaseName,
        x.itm.ProductionDate,
        x.itm.PublishedDate,
        Title = x.itm.RecordTitle,
        x.itm.UpdatedDate
    }).Distinct();

其中 TypeId 和 Id in是完成组加入（左外加入）的评论c => new { a = c.TypeId, b = c.Id }中的字段。

var recordAttachments = recordComments
    .GroupJoin(attachments,
        itm => new { a = 1, b = itm.RecordId },
        at => new { a = at.ContentType, b = at.ContentId },
        (itm, at) => new { at, itm})
    .SelectMany(x => x.at.DefaultIfEmpty(), (x, y) => new
    {
        Attachments = (y != null) ? true : false,
        AttachmentsCount = x.at.Count(),
        AttachmentTitle = y.FileName,
        AttachmentId = (y != null) ? y.AttachmentId : 0,
        TypeId = (y != null) ? y.ContentType : 0,
        ItemId = (y != null) ? y.ContentId : 0,
        Comments = x.itm.Comments,
        CommentsCount = x.itm.CommentsCount,
        Featured = x.itm.Featured,
        Id = x.itm.RecordId,
        PhaseName = x.itm.PhaseName,
        x.itm.ProductionDate,
        x.itm.PublishedDate,
        Title = x.itm.Title,
        x.itm.UpdatedDate
    }).Distinct().ToList();

但是对于最后一个 lambda 表达式，存在一个问题，即如果同一记录有两个附件，则带有附件的记录会重复（不在数据库中，而是在视图中）。

如此处所示

 "Data": [
    {
        "typeid": 1,
        "typename": "Record Scan",
        "id": 3071,
        "title": "Late Outcomes",
        "publishdate": "3/4/2013",
        "featured": true,
        "productiondate": "",
        "phasename": "Board",
        "updateddate": "4/29/2013",
        "updateddateforsorting": "2013-04-29T19:44:29.47",
        "comments": true,
        "numofcomments": 4,
        "attachment": true,
        "numofattachments": 2,
        "attachments": [
            {
                "attachmentid": 371,
                "typeid": 1,
                "id": 0,
                "title": "Cardio_David.docx",
                "name": null,
                "createddate": "0001-01-01T00:00:00"
            },
            {
                "attachmentid": 434,
                "typeid": 1,
                "id": 0,
                "title": "blanks in password field.docx",
                "name": null,
                "createddate": "0001-01-01T00:00:00"
            }
        ]
    },
    {
        "typeid": 1,
        "typename": "Record Scan",
        "id": 3071,
        "title": "Late Outcomes",
        "publishdate": "3/4/2013",
        "featured": true,
        "productiondate": "",
        "phasename": "Board",
        "updateddate": "4/29/2013",
        "updateddateforsorting": "2013-04-29T19:44:29.47",
        "comments": true,
        "numofcomments": 4,
        "attachment": true,
        "numofattachments": 2,
        "attachments": [
            {
                "attachmentid": 371,
                "typeid": 1,
                "id": 0,
                "title": "Cardio_David.docx",
                "name": null,
                "createddate": "0001-01-01T00:00:00"
            },
            {
                "attachmentid": 434,
                "typeid": 1,
                "id": 0,
                "title": "blanks in password field.docx",
                "name": null,
                "createddate": "0001-01-01T00:00:00"
            }
        ]
    }
]

注意-这是一个示例数据，忽略我将最后一个代码recordAttachment 编辑为的字段名称和值

var recordAttachment= from rc in recordComments
                                        join at in attachments on rc.RecordId equals at.ContentId into ra
                                        select new { Comments = rc.Comments, CommentsCount = rc.CommentsCount Featured = rc.Featured, Id = rc.RecordId, PhaseName = rc.PhaseName, rc.ProductionDate, jac.PublishedDate, Source = jac.Source, Title = rc.Title, rc.UpdatedDate, AttachmentCount = ra.Count(), Attachments = ra, IsAttachment = (ra.Count() != null) ? true : false };

这将返回记录和关联的附件。现在我需要将此数据映射到视图模型..

public class FlaggedItemModel
{
    public int typeid { get; set; }
    public string typename { get; set; }
    public int id { get; set; }
    public string title { get; set; }
    public string publishdate { get; set; }     
    public bool featured { get; set; }
    public string productiondate { get; set; }
    public string phasename { get; set; }
    public string updateddate { get; set; }
    public DateTime updateddateforsorting { get; set; }
    public bool comments { get; set; }
    public int numofcomments { get; set; }
    public bool attachment { get; set; }
    public int numofattachments { get; set; }
    public IList<AttachmentModel> attachments { get; set; }
}

我试过这段代码但没有工作

var recordlist = journalArticleAttachments.Select(x => new FlaggedItemModel() {  attachments = x.Attachments.Where(z => z.ContentId == x.Id).Select(jaa => new AttachmentModel() { attachmentid = jaa.AttachmentId, typeid = jaa.ContentType, title = jaa.FileName }).ToList(), numofcomments = x.CommentsCount, comments = x.Comments, featured = x.Featured, id = x.Id, phasename = x.PhaseName, productiondate = (x.ProductionDate.HasValue) ? x.ProductionDate.Value.ToShortDateString() : string.Empty, publishdate = (x.PublishedDate.HasValue) ? x.PublishedDate.Value.ToShortDateString() : string.Empty, title = x.Title, typeid = 1, typename = "Journal Scan", updateddate = x.UpdatedDate.ToShortDateString(), updateddateforsorting = x.UpdatedDate });

如何解决这个问题？

4

1 回答 1

0

您收到此错误是因为您试图让数据库将日期时间转换为格式化的短日期字符串，但它不知道该怎么做。我建议将您的模型更改为将生产日期设置为日期时间字段，并在您的视图中对其进行适当的格式化。将日期时间更改为控制器（或 DAL）中的字符串不是合适的地方。

或者，如果您坚持在视图模型中使用短日期，请让查询最初将字段作为日期时间返回，然后在查询上调用 .ToList() ，然后将该结果投影到您的最终视图中，以便返回结果从数据库中作为日期时间，然后您可以将其转换为 C# 中的 shortdate。像这样的东西：

var recordlist = journalArticleAttachments.Select(x=>new { ..., publishdate, ...}).ToList().Select(x=>new { ..., publishdate = (publishdate==null) ? publishdate.ToShortDateString() : string.Empty, ...});

于 2015-03-15T04:39:39.477 回答