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LINQ to Entities无法识别'Double Parse(System.String)'方法，因此无法将此方法转换为存储表达式。

c#.netentity-framework
19

当我尝试运行报告时，出现了错误。问题出在这里：model.Referring = Math.Round(_newSurveyResult.Select(m => string.IsNullOrEmpty(m.Question1) ? 0 : Double.Parse(m.Question1)).Average());

public class SummaryDetails
{
    public int ChannelId { get; set; }
    public int ChannelGroupId { get; set; }
    public string Question1 { get; set; }
    public string Question2 { get; set; }
    public string Question3 { get; set; }
    public string Question4 { get; set; }
    public int OrganizationId { get; set; }
}

public ActionResult AreaManager(AreaManagerModel model)
{
    model.ShowCustomerReport = false;
    model.ShowSurveyReport = true;
    LoadModelVariablesonPostBack(model, 8);
    var _newSurveyResult = (
        from ls in SessionHandler.CurrentContext.LennoxSurveyResponses
        join ml in SessionHandler.CurrentContext.MailingListEntries on ls.SurveyCode equals ml.SurveyCode
        join m in SessionHandler.CurrentContext.MailingLists on ml.MailingListId equals m.MailingListId
        join ch in SessionHandler.CurrentContext.Channels on m.ChannelId equals ch.ChannelId
        join cg in SessionHandler.CurrentContext.ChannelGroups on ch.ChannelGroupId equals cg.ChannelGroupId
        join dcg in SessionHandler.CurrentContext.ChannelGroups on cg.ParentChannelGroupId equals dcg.ChannelGroupId
        join ncg in SessionHandler.CurrentContext.ChannelGroups on dcg.ParentChannelGroupId equals ncg.ChannelGroupId
        join pcg in SessionHandler.CurrentContext.ChannelGroups on ncg.ParentChannelGroupId equals pcg.ChannelGroupId
        select new SummaryDetails { 
            OrganizationId = ch.OrganizationId,
            Question1 = ls.Question1Answer,
            Question2 = ls.Question2Answer,
            Question3 = ls.Question3Answer,
            Question4 = ls.Question4Answer,
            ChannelId = ch.ChannelId,
            ChannelGroupId = model.TMId != 0 ? cg.ChannelGroupId : model.DistrictId != 0 ? dcg.ChannelGroupId : model.AreaId != 0 ? ncg.ChannelGroupId : model.NationId != 0 ? pcg.ChannelGroupId : model.AreaId == 0 ? ncg.ChannelGroupId : model.DistrictId == 0 ? dcg.ChannelGroupId : cg.ChannelGroupId 
        }
    );
    var _newSentSurveys = (
        from ml in SessionHandler.CurrentContext.MailingListEntries
        join m in SessionHandler.CurrentContext.MailingLists on ml.MailingListId equals m.MailingListId
        join ch in SessionHandler.CurrentContext.Channels on m.ChannelId equals ch.ChannelId
        join cg in SessionHandler.CurrentContext.ChannelGroups on ch.ChannelGroupId equals cg.ChannelGroupId
        join dcg in SessionHandler.CurrentContext.ChannelGroups on cg.ParentChannelGroupId equals dcg.ChannelGroupId
        join ncg in SessionHandler.CurrentContext.ChannelGroups on dcg.ParentChannelGroupId equals ncg.ChannelGroupId
        join pcg in SessionHandler.CurrentContext.ChannelGroups on ncg.ParentChannelGroupId equals pcg.ChannelGroupId
        where (ml.EmailDate != null || ml.LetterDate != null || ml.EmailBounce == null)
        select new SummaryDetails 
        { 
            OrganizationId = ch.OrganizationId,
            ChannelId = ch.ChannelId,
            ChannelGroupId = model.TMId != 0 ? cg.ChannelGroupId : model.DistrictId != 0 ? dcg.ChannelGroupId : model.AreaId != 0 ? ncg.ChannelGroupId : model.NationId != 0 ? pcg.ChannelGroupId : model.AreaId == 0 ? ncg.ChannelGroupId : model.DistrictId == 0 ? dcg.ChannelGroupId : cg.ChannelGroupId 
        }
    );
    if (model.ChannelId != 0)
    {
        _newSurveyResult = _newSurveyResult.Where(p => p.ChannelId == model.ChannelId);
        _newSentSurveys = _newSentSurveys.Where(p => p.ChannelId == model.ChannelId);
    }
    else if (model.TMId != 0)
    {
        _newSurveyResult = _newSurveyResult.Where(p => p.ChannelGroupId == model.TMId);
        _newSentSurveys = _newSentSurveys.Where(p => p.ChannelGroupId == model.TMId);
    }
    else if (model.DistrictId != 0)
    {
        _newSurveyResult = _newSurveyResult.Where(p => p.ChannelGroupId == model.DistrictId);
        _newSentSurveys = _newSentSurveys.Where(p => p.ChannelGroupId == model.DistrictId);
    }
    else if (model.AreaId != 0)
    {
        _newSurveyResult = _newSurveyResult.Where(p => p.ChannelGroupId == model.AreaId);
        _newSentSurveys = _newSentSurveys.Where(p => p.ChannelGroupId == model.AreaId);
    }
    else if (model.NationId != 0)
    {
        _newSurveyResult = _newSurveyResult.Where(p => p.ChannelGroupId == model.NationId);
        _newSentSurveys = _newSentSurveys.Where(p => p.ChannelGroupId == model.NationId);
    }
    else if (model.NationId == 0)
    {
        _newSurveyResult = _newSurveyResult.Where(p => p.OrganizationId == 8);
        _newSentSurveys = _newSentSurveys.Where(p => p.OrganizationId == 8);
    }
    else if (model.AreaId == 0)
    {
        _newSurveyResult = _newSurveyResult.Where(p => p.ChannelGroupId == model.LoggedChannelGroupId);
        _newSentSurveys = _newSentSurveys.Where(p => p.ChannelGroupId == model.LoggedChannelGroupId);
    }
    else if (model.DistrictId == 0)
    {
        _newSurveyResult = _newSurveyResult.Where(p => p.ChannelGroupId == model.LoggedChannelGroupId);
        _newSentSurveys = _newSentSurveys.Where(p => p.ChannelGroupId == model.LoggedChannelGroupId);
    }
    else if (model.TMId == 0)
    {
        _newSurveyResult = _newSurveyResult.Where(p => p.ChannelGroupId == model.LoggedChannelGroupId);
        _newSentSurveys = _newSentSurveys.Where(p => p.ChannelGroupId == model.LoggedChannelGroupId);
    }
    model.SentSurveys = _newSentSurveys.Count() > 0 ? _newSentSurveys.Count() : 0;
    model.CompletedSurveys = _newSurveyResult.Count() > 0 ? _newSurveyResult.Count() : 0;
    model.PercentageComplete = model.SentSurveys != 0 ? (Convert.ToDouble(model.CompletedSurveys) / Convert.ToDouble(model.SentSurveys)) : 0;
    if (_newSurveyResult.Count() > 0)
    {
        model.Referring = Math.Round(_newSurveyResult.Select(m => string.IsNullOrEmpty(m.Question1) ? 0 : Double.Parse(m.Question1)).Average());
        model.ServicePerformance = Math.Round(_newSurveyResult.Select(m => string.IsNullOrEmpty(m.Question2) ? 0 : Double.Parse(m.Question2)).Average());
        model.InstallPerformance = Math.Round(_newSurveyResult.Select(m => string.IsNullOrEmpty(m.Question3) ? 0 : Double.Parse(m.Question3)).Average());
        model.ReferringLennox = Math.Round(_newSurveyResult.Select(m => string.IsNullOrEmpty(m.Question4) ? 0 : Double.Parse(m.Question4)).Average());
        double overAllScore = CalculateOverallScore(
                _newSurveyResult.Select(m => string.IsNullOrEmpty(m.Question1) ? 0 : Double.Parse(m.Question1)).Sum(),
                _newSurveyResult.Select(m => string.IsNullOrEmpty(m.Question2) ? 0 : Double.Parse(m.Question2)).Sum(),
                _newSurveyResult.Select(m => string.IsNullOrEmpty(m.Question3) ? 0 : Double.Parse(m.Question3)).Sum(),
                _newSurveyResult.Select(m => string.IsNullOrEmpty(m.Question4) ? 0 : Double.Parse(m.Question4)).Sum(),
                _newSurveyResult.Count());
        model.OverallScore = Math.Round(overAllScore);
    }
}
1个回答
50
这里的问题是您的查询被翻译成 SQL 并在数据库上运行，而 Entity Framework 不知道如何将 Double.Parse 转换为有效的 SQL 代码。不过，您可以定义一个自定义方法来执行解析，并告诉 Entity Framework 如何将该方法转换为 SQL。以下是操作步骤： 定义翻译 打开文本编辑器中的 *.edmx 文件，查找 <edmx:ConceptualModels> 标记。在其下面，应该看到一个 <Schema Namespace="YourModel" ...> 标记。在 Schema 标记内部，添加以下内容：
    <Function Name="ParseDouble" ReturnType="Edm.Double"> 
        <Parameter Name="stringvalue" Type="Edm.String" /> 
        <DefiningExpression> 
            cast(stringvalue as Edm.Double)
        </DefiningExpression> 
    </Function>

这定义了你的自定义ParseDouble函数将被翻译成的Enity-SQL代码。

创建一个需要翻译的方法

现在我们需要在代码中定义一个匹配函数，以便您可以将其放入LINQ语句中。您的EDMX文件用于生成一个继承自ObjectContext的部分类。由于它是一个部分类，因此您可以添加自己的方法而不触及生成的代码 - 只需确保类名匹配即可。

using System.Data.Objects.DataClasses;

public partial class YourObjectContext
{
    /// <summary>
    ///     This method exists for use in LINQ queries,
    ///     as a stub that will be converted to a SQL CAST statement.
    /// </summary>
    [EdmFunction("YourModel", "ParseDouble")]
    public static double ParseDouble(string stringvalue)
    {
        return Double.Parse(stringvalue);
    }
}

现在，您可以回到LINQ语句，将任何Double.Parse的实例替换为YourObjectContext.ParseDouble。由于这是一个实际调用Double.Parse的方法，因此它可以用于LINQ对对象的调用；同时，由于它也在EDMX文件中定义，因此LINQ对实体也可以将其翻译成SQL。

但等一下，您还没有完成！

我注意到您的LINQ语句还包括对Math.Round的调用。我不知道Entity Framework是否包括该方法的转换，但如果没有，在您修复Double.Parse的错误后，您将为该方法获得相同的错误。幸运的是，那种情况的解决方案几乎完全相同，只不过在EDMX文件中定义的函数会是这样：

    <Function Name="Round" ReturnType="Edm.Double"> 
        <Parameter Name="input" Type="Edm.Double" /> 
        <DefiningExpression> 
            Round(input)
        </DefiningExpression> 
    </Function>

您可以使用此EDM规范函数列表来查看可放置在<DefiningExpression>标签内的有效内容。

4
此外，在 SQLFunctions 类中有一堆预定义的函数（不过我认为你所需要的函数不在其中）。http://msdn.microsoft.com/en-us/library/dd466169.aspx - Slappy
对于使用EF的Math.Round函数，您可以使用重载版本Math.Round(1.2345, 2, MidpointRounding.AwayFromZero)。 - Stanislav
1
linqPad误导了我。Math.Round(1.2345, 2, MidpointRounding.AwayFromZero)只在linq2sql中有效，而在EF中无效。 - Stanislav
2
我需要在Code First EF 6.1中完成这个任务。 - Rhyous
2
DbFunction 不必在对象/数据库上下文上定义。它可以在任何地方定义。我已经使用静态类进行了测试，使我能够将其定义为扩展方法。（对于我的需求：public static int? ToInt(this string stringValue)。） - Frédéric
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