So I've seen a few posts describing this, but can't quite figure it out for my case. I used to have a SQL query that used the PIVOT command to order my table, I am trying to move this logic into our app via LINQ. The table is stored in a DataTable and looks like this.
ObjectName | ColumnName | Property | Value
----------------------------------------------
foo | bar | a | w
foo | bar | b | x
foo | bar | c | y
foo | bar | d | z
foo | test | a | i
foo | test | b | j
foo | test | c | k
foo | test | d | l
I want to morph it into a DataTable that looks like this.
ObjectName | ColumnName | a | b | c | d
---------------------------------------------------
foo | bar | w | x | y | z
foo | test | i | j | k | l
So I tried something like this...
var query = dt.AsEnumerable()
.GroupBy(row => row.Field<string>("ColumnName"))
.Select(g => new {
ColumnName = g.Key,
a = g.Where(row => row.Field<string>("Property") == "a").Select(c => c.Field<string>("Value")),
b = g.Where(row => row.Field<string>("Property") == "b").Select(c => c.Field<string>("Value")),
c = g.Where(row => row.Field<string>("Property") == "c").Select(c => c.Field<string>("Value")),
d = g.Where(row => row.Field<string>("Property") == "d").Select(c => c.Field<string>("Value"))
});
Which doesn't include ObjectName (for some reason was giving me a compile error to add it?). Looking at the debugger ColumnName is showing up right, but the rest is mostly gibberish. Sorry my LINQ skills are pretty sub-par, I'm trying to learn, but get confused easily.
I'm guessing my datatype isn't coming out correctly to be able to use that extension method, but I'm in a bit over my head. Any suggestions?
Edit still getting some errors, I am fighting with this line
DataTable newDT = query.CopyToDataTable();
but I get the error message
The type 'AnonymousType#1' cannot be used as type parameter 'T' in
the generic type or method
'System.Data.DataTableExtensions.CopyToDataTable
(System.Collections.Generic.IEnumerable)'. There is no implicit
reference conversion from 'AnonymousType#1' to 'System.Data.DataRow'.
Try this:
class Program
{
//Helper method to make the Select cleaner:
private static string GetProperty(IEnumerable<DataRow> rows, string propertyName)
{
return rows
.Where(row => row.Field<string>("Property") == propertyName)
.Select(c => c.Field<string>("Value"))
.FirstOrDefault();
}
//helper method for populating the datatable
private static void addRow(DataTable dt, string objectName, string columnName
, string property, string value)
{
var row = dt.NewRow();
row["ObjectName"] = objectName;
row["ColumnName"] = columnName;
row["Property"] = property;
row["Value"] = value;
dt.Rows.Add(row);
}
public static void Main(string[] args)
{
DataTable dt = new DataTable();
dt.Columns.Add("ObjectName");
dt.Columns.Add("ColumnName");
dt.Columns.Add("Property");
dt.Columns.Add("Value");
addRow(dt, "foo", "bar", "a", "w");
addRow(dt, "foo", "bar", "b", "x");
addRow(dt, "foo", "bar", "c", "y");
addRow(dt, "foo", "bar", "d", "z");
addRow(dt, "foo", "test", "a", "i");
addRow(dt, "foo", "test", "b", "j");
addRow(dt, "foo", "test", "c", "k");
addRow(dt, "foo", "test", "d", "l");
var query = dt.AsEnumerable()
.GroupBy(row => new
{
ObjectName = row.Field<string>("ObjectName"),
ColumnName = row.Field<string>("ColumnName")
})
.Select(g => new
{
ObjectName = g.Key.ObjectName,
ColumnName = g.Key.ColumnName,
a = GetProperty(g, "a"),
b = GetProperty(g, "b"),
c = GetProperty(g, "c"),
d = GetProperty(g, "d"),
})
.CopyToDataTable();
foreach (DataRow row in query.Rows)
{
foreach (DataColumn column in query.Columns)
{
System.Console.Write(row[column] + "\t");
}
System.Console.WriteLine();
}
Console.WriteLine("Press any key to exit. . .");
Console.ReadKey(true);
}
}
Here is the code that I'm using to copy to the datattable, since you didn't state what you were using:
using System;
using System.Data;
using System.Collections.Generic;
using System.Reflection;
/// <summary>
/// Code copied directly from http://msdn.microsoft.com/en-us/library/bb669096.aspx
/// </summary>
/// <typeparam name="T"></typeparam>
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;
}
}
/// <summary>
/// Code copied directly from http://msdn.microsoft.com/en-us/library/bb669096.aspx
/// </summary>
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);
}
}
