How can i add linq query EnumerableRowCollection<TRow> to a datatable?

Question

I have this linq query:

 var lastDaysData = from myRow in rawDataSet.AsEnumerable()
                            where myRow.Field<DateTime>("DateTime") < DateTime.Now.AddHours(-24)
                            select myRow;

which i think should return the last 24 hrs worth of data from the SQL database.

i am trying to add the results of the query to a datatable with a foreach loop:

 DataTable dataTable = new DataTable();

            foreach (DataRow row in lastDaysData)
            {
                dataTable.ImportRow(row);
            }

            dataGridView1.DataSource = dataTable;

However, my datagridview is not populating with any data.

So am i adding the rows incorrectly to the datatable or is my linq query wrong?

Answer 1

Most of the time, I would say you shouldn't use DataTables in modern C#, you should use EF or LINQ to SQL and use objects directly.

But when I must work with them, I use some extension methods to make using LINQ with DataTables a bit easier.

This one converts the resulting IEnumerable<DataRow> from a LINQ query on a DataTable.AsEnumerable() back to a DataTable with a matching schema:

public static DataTable ToDataTable(this IEnumerable<DataRow> src) {
    var ans = src.First().Table.Clone();
    foreach (var r in src)
        ans.ImportRow(r);
    return ans;
}

This one let's you use anonymous objects to select out columns and then creates a new DataTable from the objects, but it uses reflection and so can be slow. It may be better to make a variation of the above ToDataTable that takes a list of column names projects the answer accordingly.

public static DataTable ToDataTable<T>(this IEnumerable<T> rows) {
    var dt = new DataTable();
    if (rows.Any()) {
        var rowType = typeof(T);
        var memberInfos = rowType.GetPropertiesOrFields();
        foreach (var info in memberInfos)
            dt.Columns.Add(new DataColumn(info.Name, info.GetMemberType()));

        foreach (var r in rows)
            dt.Rows.Add(memberInfos.Select(i => i.GetValue(r)).ToArray());
    }
    return dt;
}

You need some MemberInfo extensions to make working with properties and fields easier:

// ***
// *** Type Extensions
// ***
public static List<MemberInfo> GetPropertiesOrFields(this Type t, BindingFlags bf = BindingFlags.Public | BindingFlags.Instance) =>
    t.GetMembers(bf).Where(mi => mi.MemberType == MemberTypes.Field | mi.MemberType == MemberTypes.Property).ToList();

// ***
// *** MemberInfo Extensions
// ***
public static Type GetMemberType(this MemberInfo member) {
    switch (member) {
        case FieldInfo mfi:
            return mfi.FieldType;
        case PropertyInfo mpi:
            return mpi.PropertyType;
        case EventInfo mei:
            return mei.EventHandlerType;
        default:
            throw new ArgumentException("MemberInfo must be if type FieldInfo, PropertyInfo or EventInfo", nameof(member));
    }
}

public static object GetValue(this MemberInfo member, object srcObject) {
    switch (member) {
        case FieldInfo mfi:
            return mfi.GetValue(srcObject);
        case PropertyInfo mpi:
            return mpi.GetValue(srcObject);
        default:
            throw new ArgumentException("MemberInfo must be of type FieldInfo or PropertyInfo", nameof(member));
    }
}
public static T GetValue<T>(this MemberInfo member, object srcObject) => (T)member.GetValue(srcObject);

Finally, if you do a join across multiple DataTables, you can flatten the answer back to another DataTable with this method:

// Create new DataTable from LINQ results on DataTable
// Expect T to be anonymous object of form new { DataRow d1, DataRow d2, ... }
public static DataTable FlattenToDataTable<T>(this IEnumerable<T> src) {
    var res = new DataTable();
    if (src.Any()) {
        var firstRow = src.First();
        var rowType = typeof(T);
        var memberInfos = rowType.GetPropertiesOrFields();
        var allDC = memberInfos.SelectMany(mi => mi.GetValue<DataRow>(firstRow).Table.DataColumns());

        foreach (var dc in allDC) {
            var newColumnName = dc.ColumnName;
            if (res.ColumnNames().Contains(newColumnName)) {
                var suffixNumber = 1;
                while (res.ColumnNames().Contains($"{newColumnName}.{suffixNumber}"))
                    ++suffixNumber;
                newColumnName = $"{newColumnName}.{suffixNumber}";
            }
            res.Columns.Add(new DataColumn(newColumnName, dc.DataType));
        }

        foreach (var objRows in src)
            res.Rows.Add(memberInfos.SelectMany(mi => mi.GetValue<DataRow>(objRows).ItemArray).ToArray());
    }
    return res;
}

Answer 2

I figured it out myself in the end.

I had to add the columns i wanted to a List first, then add the list to a dataTable

     var rawDataSet = pDCDataSet.RawData;

        var lastDaysData = from myRow in rawDataSet.AsEnumerable()
                           where myRow.Field<DateTime>("DateTime") > DateTime.Now.AddHours(-Convert.ToInt32(comboBox1.Text))
                           select new
                           {
                               myRow.DateTime,
                               myRow.FolderSize,
                               myRow.FileNumber,
                               //myRow.Results,
                           };

       var newlist = lastDaysData.ToList();

        DataTable dt = new DataTable();

        dt.Columns.Add("DateTime");
        dt.Columns.Add("FolderSize");
        dt.Columns.Add("FileNumber");
        foreach (var item in newlist)
        {
            var row = dt.NewRow();

            row["DateTime"] = item.DateTime;
            row["FolderSize"] = Convert.ToString(item.FolderSize);
            row["FileNumber"] = item.FileNumber;

            dt.Rows.Add(row);
        }


        dataGridView1.DataSource = dt;