DataTable.Select
在我们实际编程的工程中，常常遇到这样的情况：DataTable并不是数据库中的，或者DataTable尚未写到数据库，或者从数据库中读出的DataTable已经在本地被改动，又没有写回数据库（可能还要作其他改动），在这些情况下，其实只要用.NET类库中提供的DataView类的强大功能（主要是用它的RowFilter属性），就能方便地解决这类查询问题。
常有网友在网上询问怎么在DataTable中执行DataTable.Select("条件")返回DataTable，今天我在这里给个解决方法给大家参考：代码如下
/// <summary>
/// 执行DataTable中的查询返回新的DataTable
/// </summary>
/// <param name="dt">源数据DataTable</param>
/// <param name="condition">查询条件</param>
/// <returns></returns>
private DataTable GetNewDataTable(DataTable dt,string condition)
{
DataTable newdt = new DataTable();
newdt=dt.Clone();
DataRow[] dr = dt.Select(condition);
for(int i=0;i<dr.Length;i++)
{
newdt.ImportRow((DataRow)dr[i]);
}
return newdt;//返回的查询结果
}
--
网友PS：
循环添加行结果也一样：
DataRow[] rows = dt.Select(conditions);
foreach(DataRow row in rows)
{
newdt.Rows.Add(row.ItemArray);
}
return newdt;
DataTable.Select方法返回获取所有DataRow对象的数组。Select()有四个重载方法.
| 名称 | 说明 | |
|---|---|---|
| Select () | 获取所有 DataRow 对象的数组。 | |
| Select(String) | 按照主键顺序（如果没有主键，则按照添加顺序）获取与筛选条件相匹配的所有 DataRow 对象的数组。 | |
| Select(String, String) | 获取按照指定的排序顺序且与筛选条件相匹配的所有 DataRow 对象的数组。 | |
| Select(String, String, DataViewRowState) | 获取与排序顺序中的筛选器以及指定的状态相匹配的所有 DataRow 对象的数组。 |
1.Select()示例：
private void GetRows()
{
// Get the DataTable of a DataSet.
DataTable table = DataSet1.Tables["Suppliers"];
DataRow[] rows = table.Select();
// Print the value one column of each DataRow.
for(int i = 0; i < rows.Length ; i++)
{
Console.WriteLine(rows[i]["CompanyName"]);
}
}
2.Select(string filterExpression)示例：
private void GetRowsByFilter()
{
DataTable table = DataSet1.Tables["Orders"];
// Presuming the DataTable has a column named Date.
string expression;
expression = "Date > #1/1/00#";
DataRow[] foundRows;
// Use the Select method to find all rows matching the filter.
foundRows = table.Select(expression);
// Print column 0 of each returned row.
for(int i = 0; i < foundRows.Length; i ++)
{
Console.WriteLine(foundRows[i][0]);
}
}
3.Select(string filterExpression,string sort)示例：
private void GetRowsByFilter()
{
DataTable table = DataSet1.Tables["Orders"];
// Presuming the DataTable has a column named Date.
string expression = "Date > '1/1/00'";
// Sort descending by column named CompanyName.
string sortOrder = "CompanyName DESC";
DataRow[] foundRows;
// Use the Select method to find all rows matching the filter.
foundRows = table.Select(expression, sortOrder);
// Print column 0 of each returned row.
for(int i = 0; i < foundRows.Length; i ++)
{
Console.WriteLine(foundRows[i][0]);
}
}
4.Select(string filterExpression,string sort, DataViewRowState recordStates)示例：
private static void GetRowsByFilter()
{
DataTable customerTable = new DataTable("Customers");
// Add columns
customerTable.Columns.Add("id", typeof(int));
customerTable.Columns.Add("name", typeof(string));
// Set PrimaryKey
customerTable.Columns[ "id" ].Unique = true;
customerTable.PrimaryKey = new DataColumn[]
{ customerTable.Columns["id"] };
// Add ten rows
for(int id=1; id<=10; id++)
{
customerTable.Rows.Add(
new object[] { id, string.Format("customer{0}", id) });
}
customerTable.AcceptChanges();
// Add another ten rows
for(int id=11; id<=20; id++)
{
customerTable.Rows.Add( new object[] { id, string.Format("customer{0}", id) });
}
string expression;
string sortOrder;
DataTable.Select方法返回获取所有DataRow对象的数组。Select()有四个重载方法.
| 名称 | 说明 | |
|---|---|---|
| Select () | 获取所有 DataRow 对象的数组。 | |
| Select(String) | 按照主键顺序（如果没有主键，则按照添加顺序）获取与筛选条件相匹配的所有 DataRow 对象的数组。 | |
| Select(String, String) | 获取按照指定的排序顺序且与筛选条件相匹配的所有 DataRow 对象的数组。 | |
| Select(String, String, DataViewRowState) | 获取与排序顺序中的筛选器以及指定的状态相匹配的所有 DataRow 对象的数组。 |
1.Select()示例：
private void GetRows()
{
// Get the DataTable of a DataSet.
DataTable table = DataSet1.Tables["Suppliers"];
DataRow[] rows = table.Select();
// Print the value one column of each DataRow.
for(int i = 0; i < rows.Length ; i++)
{
Console.WriteLine(rows[i]["CompanyName"]);
}
}
2.Select(string filterExpression)示例：
private void GetRowsByFilter()
{
DataTable table = DataSet1.Tables["Orders"];
// Presuming the DataTable has a column named Date.
string expression;
expression = "Date > #1/1/00#";
DataRow[] foundRows;
// Use the Select method to find all rows matching the filter.
foundRows = table.Select(expression);
// Print column 0 of each returned row.
for(int i = 0; i < foundRows.Length; i ++)
{
Console.WriteLine(foundRows[i][0]);
}
}
3.Select(string filterExpression,string sort)示例：
private void GetRowsByFilter()
{
DataTable table = DataSet1.Tables["Orders"];
// Presuming the DataTable has a column named Date.
string expression = "Date > '1/1/00'";
// Sort descending by column named CompanyName.
string sortOrder = "CompanyName DESC";
DataRow[] foundRows;
// Use the Select method to find all rows matching the filter.
foundRows = table.Select(expression, sortOrder);
// Print column 0 of each returned row.
for(int i = 0; i < foundRows.Length; i ++)
{
Console.WriteLine(foundRows[i][0]);
}
}
4.Select(string filterExpression,string sort, DataViewRowState recordStates)示例：
private static void GetRowsByFilter()
{
DataTable customerTable = new DataTable("Customers");
// Add columns
customerTable.Columns.Add("id", typeof(int));
customerTable.Columns.Add("name", typeof(string));
// Set PrimaryKey
customerTable.Columns[ "id" ].Unique = true;
customerTable.PrimaryKey = new DataColumn[]
{ customerTable.Columns["id"] };
// Add ten rows
for(int id=1; id<=10; id++)
{
customerTable.Rows.Add(
new object[] { id, string.Format("customer{0}", id) });
}
customerTable.AcceptChanges();
// Add another ten rows
for(int id=11; id<=20; id++)
{
customerTable.Rows.Add( new object[] { id, string.Format("customer{0}", id) });
}
string expression;
string sortOrder;
expression = "id > 5";