Question

在我的C＃代码中，我有一个来源DataTable，并希望查询它，将结果存储到另一个DataTable。

我有一个Data {stgId, fromdate, todate, colorCode, something1, something2作为列。在使用where条件查询后，我需要删除something1和something2列，并将结果输入另一个DataTable。

等效SQL查询如下所示

SELECT 
    stgId,
    fromdate,
    todate,
    colorCode 
FROM 
    tblScheduling 
WHERE 
    Mcode='123'

我希望将结果导入另一个DataTable。

编辑：回答后更新

可以使用this之类的条件将结果设为DataRow[]类型。

DataRow[] results = table.Select("A = 'foo' AND B = 'bar' AND C = 'baz'");

但是我希望结果集为新的DataTable 引用来自已接受的答案
＆＃34;了解LINQ和lambda表达式，它们对您非常有用。您可以阅读here和here＆＃34;

Answer 1

您无法直接使用CopyToDataTable方法，请参阅：How to: Implement CopyToDataTable Where the Generic Type T Is Not a DataRow。根据链接设置课程后，您可以稍后调用方法CopyToDataTable，如：

var newDataTable = (dt.AsEnumerable()
                     .Where(r=> r.Field<string>("Mcode" == "123")
                     .Select new 
                           {
                           stgId = r.Field<int>("stgId"),
                           fromdate = r.Field<DateTime>("fromdate"),
                           todate = r.Field<DateTime>("todate"),
                           colorCode = r.Field<int>("colorCode")
                           }).CopyToDataTable();

请记住在Field扩展方法中使用正确的类型。

以上要求在您的代码中设置两个类。 *（来自同一MSDN link）

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 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;
    }
}

Answer 2

foreach (DataRow dr in dataTable1.Rows) {
    if (dr["Mcode"].ToString()=="123")
        dataTable2.Rows.Add(dr.ItemArray);
}

以上示例假定dataTable1和dataTable2具有相同的数量，类型和列顺序。

编辑1

您可以使用clone方法将现有数据表的结构复制到另一个数据表中。

http://msdn.microsoft.com/en-IN/library/system.data.datatable.clone.aspx

假设您有一个数据表dt1因此您可以按如下方式创建克隆

  DataTable dt2  = dt1.Clone();

并使用上面的循环如下

foreach (DataRow dr in dt1.Rows) {
    if (dr["Mcode"].ToString()=="123")
        dt2.Rows.Add(dr.ItemArray);
}

如何在C＃中使用从一个DataTable到另一个Data Condition的条件选择列

2 个答案:

编辑1