具有相同密钥的项目已存在答案

【问题标题】：item with same key already exists具有相同密钥的项目已存在
【发布时间】：2018-09-17 21:28:20
【问题描述】：

对 LINQ 相当陌生，无法理解为什么会出现此错误：

已添加具有相同密钥的项目。

我在想是因为我使用了 3 次 select lambda 表达式？否则，从代码中，我看不到任何属性是如何被多次分配的。有没有更好的方法来写这个和解释？谢谢。

视图模型：

public class AwardWinnersViewModel
{
    public int WinnerId { get; set; }
    public string AwardName { get; set; }
    public DateTime StartDate { get; set; }
    public string Contact { get; set; }
    public int Type { get; set; }
    public int JurisdictionRef { get; set; }
    public int WorkareaRef { get; set; }
    public string Jurisdiction { get; set; }
    public string Workarea { get; set; }
    public string LogoUrl { get; set; }

}

public class AwardWinnersWrapperVM
{
    public IEnumerable<KeyValuePair<short, string>> JurisdictionFilter { get; set; }
    public IEnumerable<KeyValuePair<int, string>> WorkareaFilter { get; set; }
    public IEnumerable<AwardWinnersViewModel> AwardWinners { get; set; }
    public int Page { get; set; }
    public int WinnersPerPage { get; set; }
    public bool HasPrevious { get; set; }
    public bool HasNext { get; set; }
    public int TotalWinners { get; set; } 
    public int? ResultsOutOf { get => (this.WinnersPerPage * (this.Page + 1)) < this.TotalWinners ? (this.WinnersPerPage * (this.Page + 1)) : this.TotalWinners; }
    public int NumberOfPips { get => this.TotalWinners / WinnersPerPage; }
    public int? SelectedJurisdiction { get; set; }
    public int? SelectedWorkarea { get; set; }

}

控制器：

[HttpGet]
public async Task<ActionResult> Index(int? page, int? additionalJurisdictionSearch, int? additionalWorkareaSearch)
{
    var awardWinners = await awardWinnersService.GetAwardWinnersAsync();
    var jurisdictions = contentMetadataService.GetJurisdictions();
    var workareas = contentMetadataService.GetWorkareas();
    int pageNumber = page ?? 0;

    var viewModel = new AwardWinnersWrapperVM
    {
        TotalWinners = awardWinners.Count(),
        WinnersPerPage = winnersPerPage,
        Page = pageNumber,
        HasPrevious = pageNumber > 0,
        HasNext = awardWinners.Count() > (winnersPerPage * (pageNumber + 1)),

        AwardWinners = awardWinners.Select(x => new AwardWinnersViewModel
        {
            Type = x.Type,
            Contact = (x.Type == 1)
                ? x.WinnerId != 0 ? contributorService.GetContributor(x.WinnerId, true)?.DisplayName : string.Empty
                : x.WinnerId != 0 ? authorService.GetByRef(x.WinnerId, true)?.AuthorName : string.Empty,
            StartDate = x.StartDate,
            AwardName = x.AwardName,
            Jurisdiction = x.Jurisdiction,
            Workarea = x.Workarea,
            LogoUrl = (x.Type == 1)
                ? contributorService.GetContributor(x.WinnerId, true)?.LogoImageUrlCDN
                : authorService.GetByRef(x.WinnerId, true)?.PhotoUrl,
        }),
        JurisdictionFilter = awardWinners.Select(x => new { id = x.JurisdictionRef, display = (jurisdictions.TryGetValue((short)x.JurisdictionRef, out var jurisdiction) ? jurisdiction.JurisdictionName : string.Empty) }).ToDictionary(key => (short)key.id, val => val.display),
        WorkareaFilter = awardWinners.Select(x => new { id = x.WorkareaRef, display = (workareas.TryGetValue(x.WorkareaRef, out var workarea) ? workarea.WorkareaName : string.Empty) }).ToDictionary(key => key.id, val => val.display)
        .Skip(winnersPerPage * (pageNumber - 1))
        .Take(winnersPerPage)
    };

    return View(viewModel);
}

【问题讨论】：

你能发布异常的堆栈跟踪吗？我看到一个语法错误@PhotoUrl,，你有一个额外的逗号

标签： c# list linq controller viewmodel

【解决方案1】：

如果您的任何awardWinners 共享jurisdictionRef 或workareaRef，则ToDictionary() 调用JurisdictionFilter 和WorkareaFilter 将因该异常而失败。

我认为您只想为您的过滤器框获取不同的司法管辖区/工作区（这很可能在 ToDictionary 之前使用 .Distinct() 来实现）。

【讨论】：