HOW TO：實作通用型別 T 不是 DataRow 的 CopyToDataTable<T>

DataTable 物件通常用於資料繫結。 CopyToDataTable 方法會採用查詢的結果並將資料複製到 DataTable 中，然後此物件便可用於資料繫結。 但是，CopyToDataTable 方法只會在通用參數 T 為 DataRow 型別的 IEnumerable<T> 來源上運作。 雖然這樣非常有用，但是資料表卻無法從一序列的純量型別、傳回匿名型別的查詢或執行資料表聯結的查詢建立。

此主題描述如何實作能接受通用參數 T 型別不是 DataRow 的兩個自訂 CopyToDataTable<T> 擴充方法。 可以從 IEnumerable<T> 來源建立 DataTable 的邏輯會包含在 ObjectShredder<T> 類別中，然後再包裝到兩個多載的 CopyToDataTable<T> 擴充方法中。 ObjectShredder<T> 類別的 Shred 方法會傳回填滿的 DataTable 並接受三個輸入參數：IEnumerable<T> 來源、DataTable 以及 LoadOption 列舉。 所傳回 DataTable 的最初結構描述是根據 T 型別之結構描述而來的。 如果也提供現有的資料表做為輸入參數，則此結構描述必須與 T 型別的結構描述一致。 在所傳回的資料表中，T 型別的每一個公用屬性和欄位都會轉換為 DataColumn。 如果來源序列包含衍生自 T 的型別，則傳回的資料表結構描述會因為額外的公用屬性或欄位展開。

如需使用自訂 CopyToDataTable<T> 方法的範例，請參閱從查詢中建立 DataTable (LINQ to DataSet)。

在應用程式中實作 CopyToDataTable<T> 方法

1. 實作 ObjectShredder<T> 類別以從 IEnumerable<T> 來源建立 DataTable：

   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
   

   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;
       }
   }
   

2. 在類別中實作自訂 CopyToDataTable<T> 擴充方法：

   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
   

   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);
       }
   
   }
   

3. 將 ObjectShredder<T> 類別和 CopyToDataTable<T> 擴充方法新增到應用程式中。

   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
   

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

請參閱

概念

從查詢中建立 DataTable (LINQ to DataSet)

其他資源

程式設計手冊 (LINQ to DataSet)