Question

所以我有以下查询

        IQueryable<Feedback> query = db.Feedbacks;
        var result = query
            .Select(s => new FeedbackViewModel
            {
                businessId = s.Account.Businesses.FirstOrDefault().businessId,
                hireSuccess = s.hireSuccess.Value,
                useAgain = s.useAgain.Value,
                suggestions = s.suggestions,
                employees = numberGroups[s.numEmployees.Value]
            });
        return result;

即时收到错误

其他信息：LINQ to Entities无法识别该方法＆＃39; System.String get_Item（Int32）＆＃39;方法，这个方法不能翻译成商店表达。

由于尝试从字典查找中设置employees字符串，因此字典看起来像这样。

    public static Dictionary<int, string> numberGroups = new Dictionary<int, string>()
    {
        { 0, "None" },
        { 9, "1 to 9" },
        { 19, "10 to 19" },
        { 49, "20 to 49" },
        { 100, "50 to 100" }
    };

FeedbackViewModel看起来像这样

public class FeedbackViewModel
{
    public int businessId { get; set; }
    public bool hireSuccess { get; set; }
    public bool useAgain { get; set; }
    public string suggestions { get; set; }
    public string employees { get; set; }
}

我做错了什么？

Answer 1

我认为您正在尝试从数据库中查询某些内容。 Linq To SQL不支持numberGroups[s.numEmployees.Value]等方法。

您可以考虑做这样的事情。

          var query = db.Feedbacks.Select(f = > new
                {
                    businessId = s.Account.Businesses.FirstOrDefault().businessId,
                    hireSuccess = s.hireSuccess.Value,
                    useAgain = s.useAgain.Value,
                    suggestions = s.suggestions.Value,
                    numEmployees = s.numEmployees.Value
                }).ToList();


          var result = query
              .Select(s => new FeedbackViewModel
                {
                    businessId = s.businessId,
                    hireSuccess = s.hireSuccess,
                    useAgain = s.useAgain,
                    suggestions = s.suggestions,
                    employees = numberGroups[s.numEmployees]
                }).ToList();

Answer 2

LINQ to Entities不支持Convert.ToInt32，这可能是你的一个* .Value调用隐式执行的操作。你需要先在LINQ之外解析为int。如果我能看到FeedbackViewModel，我可能会提供更多细节。

查询根据字典查找填充字符串

2 个答案: