Postupy: Implementace CopyToDataTable<T> , kde obecný typ T není dataRow

Článek
03/02/2024

Objekt DataTable se často používá pro datová vazba. Metoda CopyToDataTable vezme výsledky dotazu a zkopíruje data do , DataTablekteré lze použít pro datovou vazbu. Metody CopyToDataTable však pracují pouze se IEnumerable<T> zdrojem, kde obecný parametr T je typu DataRow. I když je to užitečné, neumožňuje vytváření tabulek ze posloupnosti skalárních typů, z dotazů, které projektují anonymní typy, nebo z dotazů, které provádějí spojení tabulek.

Toto téma popisuje, jak implementovat dvě vlastní CopyToDataTable<T> rozšiřující metody, které přijímají obecný parametr T jiného typu než DataRow. Logika pro vytvoření DataTable ze IEnumerable<T> zdroje je obsažena ve ObjectShredder<T> třídě, která je pak zabalena do dvou přetížených CopyToDataTable<T> rozšiřujících metod. Metoda ShredObjectShredder<T> třídy vrátí vyplněný DataTable a přijímá tři vstupní parametry: IEnumerable<T> zdroj, a DataTable, a LoadOption výčet. Počáteční schéma vrácené DataTable je založeno na schématu typu T. Pokud je existující tabulka zadána jako vstup, schéma musí být konzistentní se schématem typu T. Každá veřejná vlastnost a pole typu T se převedou na vrácenou DataColumn tabulku. Pokud zdrojová sekvence obsahuje typ odvozený Tz , vrácené schéma tabulky se rozbalí pro všechny další veřejné vlastnosti nebo pole.

Příklady použití vlastních CopyToDataTable<T> metod naleznete v tématu Vytvoření datové tabulky z dotazu.

Implementace vlastních metod CopyToDataTable<T> v aplikaci

ObjectShredder<T> Implementujte třídu pro vytvoření DataTable ze IEnumerable<T> zdroje:

public class ObjectShredder<T>
{
    readonly FieldInfo[] _fi;
    readonly PropertyInfo[] _pi;
    readonly Dictionary<string, int> _ordinalMap;
    readonly 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.
        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();
        foreach (T item in source)
        {
            if (options != null)
            {
                table.LoadDataRow(ShredObject(table, item), (LoadOption)options);
            }
            else
            {
                table.LoadDataRow(ShredObject(table, item), 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.
        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())
        {
            var 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.
        var 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

Předchozí příklad předpokládá, že vlastnosti a pole nejsou DataColumn typu hodnoty null. Ke zpracování vlastností a polí s typy hodnot null použijte následující kód:

// Nullable-aware code for properties.
DataColumn dc = table.Columns.Contains(p.Name) ? table.Columns[p.Name] : table.Columns.Add(p.Name, Nullable.GetUnderlyingType(p.PropertyType) ?? p.PropertyType);

// Nullable-aware code for fields.
DataColumn dc = table.Columns.Contains(f.Name) ? table.Columns[f.Name] : table.Columns.Add(f.Name, Nullable.GetUnderlyingType(f.FieldType) ?? f.FieldType);

Implementujte vlastní CopyToDataTable<T> metody rozšíření ve třídě:

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

    public static DataTable CopyToDataTable<T>(this IEnumerable<T> source,
                                                DataTable table, LoadOption? options) =>
        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

Přidejte do ObjectShredder<T> aplikace metody třídy a CopyToDataTable<T> rozšíření.

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>
{
…
}

Postupy: Implementace CopyToDataTable<T> , kde obecný typ T není dataRow

Implementace vlastních metod CopyToDataTable<T> v aplikaci

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