Error: "The xml data type cannot be selected as DISTINCT because it is not comparable."

In my code I have the following Linq Query:

IQueryable<Data> charts = (from report in ctx.Charts group report by new 
    { 
        Name = report.ChartTitle.ChartType.ChartCategory.CategoryName,
        id = report.ChartTitle.ChartType.ChartCategory.ChartCategoryId, 
        Period = report.Period 
    } into d
    select new Data
    {
        Name = d.Key.Name,
        Id = d.Key.id,
        Period = d.Key.Period,            
        Reports = from r in d group r by new 
        { Title = r.ChartTitle.Name, id = r.ChartTitle.ChartTitleId } into rs
        select new Report
        {
            Title = rs.Key.Title,
            Id = rs.Key.id,
            Charts = (from c in rs group c by new 
                    { 
                        ChartId = c.ChartId, 
                        FiscalYear = c.FiscalYear, 
                        ModifiedDate = c.ChartView.ModifiedDate, 
                        Function = c.Function.DisplayName, 
开发者_如何转开发                        ChartData=c.ChartView.ViewData
                    } into cs
                    select new ChartInfo 
                    { 
                        ChartId = cs.Key.ChartId, 
                        FiscalYear = cs.Key.FiscalYear,
                        ModifiedDate = cs.Key.ModifiedDate, 
                        Function = cs.Key.Function, 
                        ChartData=cs.Key.ChartData 
                    })
    }});

In the above code if I exclude the "ChartData" field (which is of XML datatype), the query executes fine. But when ever I include this field it throws the following error :"The xml data type cannot be selected as DISTINCT because it is not comparable."

Let me know what I am missing here?

You can't group by XML types. This is a SQL restriction, not a LINQ-to-SQL retriction. (See Group by on XML column field with LINQ and select an xml type column in select query with group by SQL Server 2008)

Do you need to group by the XML column? The alternative would be to group by your other columns and then select the first XML value as a result.

Charts = (from c in rs group c by new  
{
    ChartId = c.ChartId,
    FiscalYear = c.FiscalYear,
    ModifiedDate = c.ChartView.ModifiedDate,
    Function = c.Function.DisplayName,
} into cs                     
select new ChartInfo
{
    ChartId = cs.Key.ChartId,
    FiscalYear = cs.Key.FiscalYear,
    ModifiedDate = cs.Key.ModifiedDate,
    Function = cs.Key.Function,
    ChartData=cs.Value.FirstOrDefault().ChartData
}) 

When using LINQ-to-SQL the items being grouped are still accessible - you don't need to include every 'selected' property / column in the group by` clause like you would in SQL.

You did not tell us what is the actual datatype of the ChartData, but from the error you are describing it looks like the problem is that whatever this datatype is it does not implement the IComparable interface which is a required interface if you want instances of the datatype to be comparable