Wie [group by] die datatable und das Ergebnis in einer anderen datatable?

GroupBy werden Sie wieder ein IGrouping Sammlung, die Sie Durchlaufen folgende Weise:

var dataTable = new DataTable();
dataTable.Columns.Add("id", typeof(Int16));
dataTable.Columns.Add("name_in", typeof(string));
foreach (var group in groups)
{
  dataTable.Rows.Add(group.Key, (group.First())["name_in"]);
}

Könnte man erstellen Sie Ihre eigenen CopyToDataTable, dass nimmt jede Art von IEnumerable(nicht nur DataRow)und liefert eine neue DataTable:

var q=from row in Process_dt.AsEnumerable()
      group row by (int)row["id"] into IdGroup
      select new{id=IdGroup.Key,name=IdGroup.First()["name"]};
//following does not compile by default
//because input is not an IEnumerable<DataRow> but an anonymous type, you need code below
var tblResult = q.CopyToDataTable(); 

Hier ist eine Umsetzung (mit Hilfe von MSDN):

public class ObjectShredder<T> {
    private System.Reflection.FieldInfo[] _fi;
    private System.Reflection.PropertyInfo[] _pi;
    private System.Collections.Generic.Dictionary<string, int> _ordinalMap;
    private System.Type _type;

    //ObjectShredder constructor.
    public ObjectShredder() {
        _type = typeof(T);
        _fi = _type.GetFields();
        _pi = _type.GetProperties();
        _ordinalMap = new Dictionary<string, int>();
    }

    ///<summary>
    ///Loads a DataTable from a sequence of objects.
    ///</summary>
    ///<param name="source">The sequence of objects to load into the DataTable.</param>
    ///<param name="table">The input table. The schema of the table must match that 
    ///the type T.  If the table is null, a new table is created with a schema 
    ///created from the public properties and fields of the type T.</param>
    ///<param name="options">Specifies how values from the source sequence will be applied to 
    ///existing rows in the table.</param>
    ///<returns>A DataTable created from the source sequence.</returns>
    public DataTable Shred(IEnumerable<T> source, DataTable table, LoadOption? options) {
        //Load the table from the scalar sequence if T is a primitive type.
        if (typeof(T).IsPrimitive) {
            return ShredPrimitive(source, table, options);
        }

        //Create a new table if the input table is null.
        if (table == null) {
            table = new DataTable(typeof(T).Name);
        }

        //Initialize the ordinal map and extend the table schema based on type T.
        table = ExtendTable(table, typeof(T));

        //Enumerate the source sequence and load the object values into rows.
        table.BeginLoadData();
        using (IEnumerator<T> e = source.GetEnumerator()) {
            while (e.MoveNext()) {
                if (options != null) {
                    table.LoadDataRow(ShredObject(table, e.Current), (LoadOption)options);
                } else {
                    table.LoadDataRow(ShredObject(table, e.Current), true);
                }
            }
        }
        table.EndLoadData();

        //Return the table.
        return table;
    }

    public DataTable ShredPrimitive(IEnumerable<T> source, DataTable table, LoadOption? options) {
        //Create a new table if the input table is null.
        if (table == null) {
            table = new DataTable(typeof(T).Name);
        }

        if (!table.Columns.Contains("Value")) {
            table.Columns.Add("Value", typeof(T));
        }

        //Enumerate the source sequence and load the scalar values into rows.
        table.BeginLoadData();
        using (IEnumerator<T> e = source.GetEnumerator()) {
            Object[] values = new object[table.Columns.Count];
            while (e.MoveNext()) {
                values[table.Columns["Value"].Ordinal] = e.Current;

                if (options != null) {
                    table.LoadDataRow(values, (LoadOption)options);
                } else {
                    table.LoadDataRow(values, true);
                }
            }
        }
        table.EndLoadData();

        //Return the table.
        return table;
    }

    public object[] ShredObject(DataTable table, T instance) {

        FieldInfo[] fi = _fi;
        PropertyInfo[] pi = _pi;

        if (instance.GetType() != typeof(T)) {
            //If the instance is derived from T, extend the table schema
            //and get the properties and fields.
            ExtendTable(table, instance.GetType());
            fi = instance.GetType().GetFields();
            pi = instance.GetType().GetProperties();
        }

        //Add the property and field values of the instance to an array.
        Object[] values = new object[table.Columns.Count];
        foreach (FieldInfo f in fi) {
            values[_ordinalMap[f.Name]] = f.GetValue(instance);
        }

        foreach (PropertyInfo p in pi) {
            values[_ordinalMap[p.Name]] = p.GetValue(instance, null);
        }

        //Return the property and field values of the instance.
        return values;
    }

    public DataTable ExtendTable(DataTable table, Type type) {
        //Extend the table schema if the input table was null or if the value 
        //in the sequence is derived from type T.            
        foreach (FieldInfo f in type.GetFields()) {
            if (!_ordinalMap.ContainsKey(f.Name)) {
                //Add the field as a column in the table if it doesn't exist
                //already.
                DataColumn dc = table.Columns.Contains(f.Name) ? table.Columns[f.Name]
                    : table.Columns.Add(f.Name, f.FieldType);

                //Add the field to the ordinal map.
                _ordinalMap.Add(f.Name, dc.Ordinal);
            }
        }
        foreach (PropertyInfo p in type.GetProperties()) {
            if (!_ordinalMap.ContainsKey(p.Name)) {
                //Add the property as a column in the table if it doesn't exist
                //already.
                DataColumn dc = table.Columns.Contains(p.Name) ? table.Columns[p.Name]
                    : table.Columns.Add(p.Name, p.PropertyType);

                //Add the property to the ordinal map.
                _ordinalMap.Add(p.Name, dc.Ordinal);
            }
        }

        //Return the table.
        return table;
    }
}

Nun können Sie diese Erweiterungen:

public static class CustomLINQtoDataSetMethods {
    public static DataTable CopyToDataTable<T>(this IEnumerable<T> source) {
        return new ObjectShredder<T>().Shred(source, null, null);
    }

    public static DataTable CopyToDataTable<T>(this IEnumerable<T> source,
                                                DataTable table, LoadOption? options) {
        return new ObjectShredder<T>().Shred(source, table, options);
    }

}

Voilà! Jetzt CopyToDataTable arbeitet mit einer LINQ-Abfrage an 🙂