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C#中含有LINQ的实用数据
原标题:Populate DataTable with LINQ in C#
  • 时间:2009-09-10 12:32:23
  •  标签:

在我看来,有人使用以下代码表示:

DataTable dt = this.attachmentsDataSet.Tables["Attachments"];

foreach (Outlook.Attachment attachment in this.mailItem.Attachments)
{
    DataRow dr = dt.NewRow();
    dr["Index"] = attachment.Index;
    dr["DisplayName"] = String.Format(
        CultureInfo.InvariantCulture,
        "{0} ({1})", 
        attachment.FileName,
        FormatSize(attachment.Size));
    dr["Name"] = attachment.FileName;
    dr["Size"] = attachment.Size;

    dt.Rows.Add(dr);
}

我很想知道,我是否能够利用LINQ实现同样的功能,以缩短这一代码。 任何想法?

最佳回答

这部法典很短或林克,但我采取了一种独一无二的方法,它带走了一名伊列主义者,将其变为可供你使用的数据。

    public static DataTable ToDataTable<T>(this IList<T> theList)
    {
        DataTable theTable = CreateTable<T>();
        Type theEntityType = typeof(T);

        // Use reflection to get the properties of the generic type (T)
        PropertyDescriptorCollection theProperties = TypeDescriptor.GetProperties(theEntityType);

        // Loop through each generic item in the list
        foreach (T theItem in theList)
        {
            DataRow theRow = theTable.NewRow();

            // Loop through all the properties
            foreach (PropertyDescriptor theProperty in theProperties)
            {
                // Retrieve the value and check to see if it is null
                object thePropertyValue = theProperty.GetValue(theItem);
                if (null == thePropertyValue)
                {
                    // The value is null, so we need special treatment, because a DataTable does not like null, but is okay with DBNull.Value
                    theRow[theProperty.Name] = DBNull.Value;
                }
                else
                {
                    // No problem, just slap the value in
                    theRow[theProperty.Name] = theProperty.GetValue(theItem);
                }
            }

            theTable.Rows.Add(theRow);
        }

        return theTable;
    }
问题回答

是的,容易

    public void FillFromList(List<T> col)
    {
        Type elementType = typeof(T);

        // Nested query of generic element list of property
        // values (using a join to the DataTable columns)
        var rows = from row in col
                   select new
                   {
                       Fields = from column in m_dataTable.Columns.Cast<DataColumn>()
                                join prop in elementType.GetProperties()
                                  on column.Caption equals prop.Name
                                select prop.GetValue(row, null)
                   };

        // Add each row to the DataTable
        int recordCount = 0;
        foreach ( var entry in rows )
        {
            m_dataTable.Rows.Add(entry.Fields.ToArray());
        }

这假设T上的特性与可数据列栏相同。

You first identify whether you can query this.mailItem.Attachments and if it is possible, you can convert query result to a datatable from extension method create by Steve Sloka...





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