Procedura: Implementazione di CopyToDataTable<T> quando il tipo generico T non è un DataRowHow to: Implement CopyToDataTable<T> Where the Generic Type T Is Not a DataRow

L'oggetto DataTable viene spesso usato per l'associazione dati.The DataTable object is often used for data binding. Il metodo CopyToDataTable copia i dati dei risultati di una query in un oggetto DataTable che può essere quindi usato per l'associazione dati.The CopyToDataTable method takes the results of a query and copies the data into a DataTable, which can then be used for data binding. I metodi CopyToDataTable, tuttavia, funzionano solo su un'origine IEnumerable<T> in cui il parametro generico T è di tipo DataRow.The CopyToDataTable methods, however, only operate on an IEnumerable<T> source where the generic parameter T is of type DataRow. Sebbene sia utile, questa funzionalità non consente di creare tabelle da una sequenza di tipi scalari, da query che proiettano tipo anonimi o da query che eseguono join di tabelle.Although this is useful, it does not allow tables to be created from a sequence of scalar types, from queries that project anonymous types, or from queries that perform table joins.

In questo argomento viene descritto come implementare due metodi di estensione CopyToDataTable<T> personalizzati che accettano un parametro generico T di un tipo diverso da DataRow.This topic describes how to implement two custom CopyToDataTable<T> extension methods that accept a generic parameter T of a type other than DataRow. La logica per creare un oggetto DataTable da un'origine IEnumerable<T> è contenuto nella classe ObjectShredder<T>, di cui viene eseguito il wrapping in due metodi di estensione CopyToDataTable<T> di overload.The logic to create a DataTable from an IEnumerable<T> source is contained in the ObjectShredder<T> class, which is then wrapped in two overloaded CopyToDataTable<T> extension methods. Il metodo Shred della classe ObjectShredder<T> restituisce l'oggetto DataTable compilato e accetta tre parametri di input: un'origine IEnumerable<T>, un oggetto DataTable e un'enumerazione LoadOption.The Shred method of the ObjectShredder<T> class returns the filled DataTable and accepts three input parameters: an IEnumerable<T> source, a DataTable, and a LoadOption enumeration. Lo schema iniziale dell'oggetto DataTable restituito è basato sullo schema del tipo T.The initial schema of the returned DataTable is based on the schema of the type T. Se viene fornita una tabella esistente come input, lo schema deve essere coerente con lo schema del tipo T.If an existing table is provided as input, the schema must be consistent with the schema of the type T. Tutte le proprietà e i campi pubblici del tipo T vengono convertiti in DataColumn nella tabella restituita.Each public property and field of the type T is converted to a DataColumn in the returned table. Se la sequenza di origine contiene un tipo derivato da T, lo schema della tabella restituita viene espanso per includere eventuali proprietà o campi pubblici aggiuntivi.If the source sequence contains a type derived from T, the returned table schema is expanded for any additional public properties or fields.

Per esempi di uso dei metodi CopyToDataTable<T> personalizzati, vedere Creazione di un oggetto DataTable da una query.For examples of using the custom CopyToDataTable<T> methods, see Creating a DataTable From a Query.

Per implementare i metodi CopyToDataTable<T> personalizzati nell'applicazioneTo implement the custom CopyToDataTable<T> methods in your application

  1. Implementare la classe ObjectShredder<T> per creare un oggetto DataTable da un'origine IEnumerable<T>:Implement the ObjectShredder<T> class to create a DataTable from an IEnumerable<T> source:

    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;
        }
    }
    
    Public Class ObjectShredder(Of T)
        ' Fields
        Private _fi As FieldInfo()
        Private _ordinalMap As Dictionary(Of String, Integer)
        Private _pi As PropertyInfo()
        Private _type As Type
    
        ' Constructor 
        Public Sub New()
            Me._type = GetType(T)
            Me._fi = Me._type.GetFields
            Me._pi = Me._type.GetProperties
            Me._ordinalMap = New Dictionary(Of String, Integer)
        End Sub
    
        Public Function ShredObject(ByVal table As DataTable, ByVal instance As T) As Object()
            Dim fi As FieldInfo() = Me._fi
            Dim pi As PropertyInfo() = Me._pi
            If (Not instance.GetType Is GetType(T)) Then
                ' If the instance is derived from T, extend the table schema
                ' and get the properties and fields.
                Me.ExtendTable(table, instance.GetType)
                fi = instance.GetType.GetFields
                pi = instance.GetType.GetProperties
            End If
    
            ' Add the property and field values of the instance to an array.
            Dim values As Object() = New Object(table.Columns.Count - 1) {}
            Dim f As FieldInfo
            For Each f In fi
                values(Me._ordinalMap.Item(f.Name)) = f.GetValue(instance)
            Next
            Dim p As PropertyInfo
            For Each p In pi
                values(Me._ordinalMap.Item(p.Name)) = p.GetValue(instance, Nothing)
            Next
    
            ' Return the property and field values of the instance.
            Return values
        End Function
    
    
        ' Summary:           Loads a DataTable from a sequence of objects.
        ' source parameter:  The sequence of objects to load into the DataTable.</param>
        ' table parameter:   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.
        ' options parameter: Specifies how values from the source sequence will be applied to 
        '                    existing rows in the table.
        ' Returns:           A DataTable created from the source sequence.
    
        Public Function Shred(ByVal source As IEnumerable(Of T), ByVal table As DataTable, ByVal options As LoadOption?) As DataTable
    
            ' Load the table from the scalar sequence if T is a primitive type.
            If GetType(T).IsPrimitive Then
                Return Me.ShredPrimitive(source, table, options)
            End If
    
            ' Create a new table if the input table is null.
            If (table Is Nothing) Then
                table = New DataTable(GetType(T).Name)
            End If
    
            ' Initialize the ordinal map and extend the table schema based on type T.
            table = Me.ExtendTable(table, GetType(T))
    
            ' Enumerate the source sequence and load the object values into rows.
            table.BeginLoadData()
            Using e As IEnumerator(Of T) = source.GetEnumerator
                Do While e.MoveNext
                    If options.HasValue Then
                        table.LoadDataRow(Me.ShredObject(table, e.Current), options.Value)
                    Else
                        table.LoadDataRow(Me.ShredObject(table, e.Current), True)
                    End If
                Loop
            End Using
            table.EndLoadData()
    
            ' Return the table.
            Return table
        End Function
    
    
        Public Function ShredPrimitive(ByVal source As IEnumerable(Of T), ByVal table As DataTable, ByVal options As LoadOption?) As DataTable
            ' Create a new table if the input table is null.
            If (table Is Nothing) Then
                table = New DataTable(GetType(T).Name)
            End If
            If Not table.Columns.Contains("Value") Then
                table.Columns.Add("Value", GetType(T))
            End If
    
            ' Enumerate the source sequence and load the scalar values into rows.
            table.BeginLoadData()
            Using e As IEnumerator(Of T) = source.GetEnumerator
                Dim values As Object() = New Object(table.Columns.Count - 1) {}
                Do While e.MoveNext
                    values(table.Columns.Item("Value").Ordinal) = e.Current
                    If options.HasValue Then
                        table.LoadDataRow(values, options.Value)
                    Else
                        table.LoadDataRow(values, True)
                    End If
                Loop
            End Using
            table.EndLoadData()
    
            ' Return the table.
            Return table
        End Function
    
        Public Function ExtendTable(ByVal table As DataTable, ByVal type As Type) As DataTable
            ' Extend the table schema if the input table was null or if the value 
            ' in the sequence is derived from type T.
            Dim f As FieldInfo
            Dim p As PropertyInfo
    
            For Each f In type.GetFields
                If Not Me._ordinalMap.ContainsKey(f.Name) Then
                    Dim dc As DataColumn
    
                    ' Add the field as a column in the table if it doesn't exist
                    ' already.
                    dc = IIf(table.Columns.Contains(f.Name), table.Columns.Item(f.Name), table.Columns.Add(f.Name, f.FieldType))
    
                    ' Add the field to the ordinal map.
                    Me._ordinalMap.Add(f.Name, dc.Ordinal)
                End If
                
            Next
    
            For Each p In type.GetProperties
                If Not Me._ordinalMap.ContainsKey(p.Name) Then
                    ' Add the property as a column in the table if it doesn't exist
                    ' already.
                    Dim dc As DataColumn
                    dc = IIf(table.Columns.Contains(p.Name), table.Columns.Item(p.Name), table.Columns.Add(p.Name, p.PropertyType))
    
                    ' Add the property to the ordinal map.
                    Me._ordinalMap.Add(p.Name, dc.Ordinal)
                End If
            Next
    
            ' Return the table.
            Return table
        End Function
    
    End Class
    

    L'esempio precedente presuppone che le proprietà di DataColumn non abbiano tipi nullable.The preceding example assumes that the properties of the DataColumn are not nullable types. Per gestire le proprietà con tipi nullable, usare il codice seguente:To handle properties with nullable types, use the following code:

    DataColumn dc = table.Columns.Contains(p.Name) ? table.Columns[p.Name] : table.Columns.Add(p.Name, Nullable.GetUnderlyingType(p.PropertyType) ?? p.PropertyType);
    
  2. Implementare i metodi di estensione CopyToDataTable<T> personalizzati in una classe:Implement the custom CopyToDataTable<T> extension methods in a class:

    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);
        }
    
    }
    
    Public Module CustomLINQtoDataSetMethods
        <Extension()> _
        Public Function CopyToDataTable(Of T)(ByVal source As IEnumerable(Of T)) As DataTable
            Return New ObjectShredder(Of T)().Shred(source, Nothing, Nothing)
        End Function
    
        <Extension()> _
        Public Function CopyToDataTable(Of T)(ByVal source As IEnumerable(Of T), ByVal table As DataTable, ByVal options As LoadOption?) As DataTable
            Return New ObjectShredder(Of T)().Shred(source, table, options)
        End Function
    
    End Module
    
  3. Aggiungere la classe ObjectShredder<T> e i metodi di estensione CopyToDataTable<T> all'applicazione.Add the ObjectShredder<T> class and CopyToDataTable<T> extension methods to your application.

Module Module1  
    Sub Main()  
        ' Your application code using CopyToDataTable<T>.  
    End Sub  
End Module  

Public Module CustomLINQtoDataSetMethods  
…  
End Module  

Public Class ObjectShredder(Of T)  
…  
End Class
class Program  
{  
    static void Main(string[] args)  
    {  
        // Your application code using CopyToDataTable<T>.  
    }  
}  
public static class CustomLINQtoDataSetMethods  
{  
…  
}  
public class ObjectShredder<T>  
{  
…  
}  

Vedere ancheSee Also

Creazione di un oggetto DataTable da una queryCreating a DataTable From a Query
Guida per programmatoriProgramming Guide