在日常开发中很少使到DataTable实现业务，因此知道DataTable的用法并不多，除了普通的查询以及排序。现在分享一个DataTable中的运算函数Compute，它能帮助我们直接使用DataTable进行求和、求个数等操作，这对于数据后加工挺有效果，因此分享一下，用法如下：
函数名：Compute
参数1：expression 表达式
参数2：filter 条件表达式
如：dataTable1中包含了ID，QTY(数量)两个字段
ID QTY
1 4
2 5
3 6
现在需要求ID大于1的和
var sum=dataTable1.Compute("Sum(QTY)","ID>1");
既可以实现，有点需要注意的地方就是，要进行聚合函数的列必须定义成数字类型，如int,decimal等。
static void Main(string[] args)
{
var dataTable1= InitDataTable();
Console.WriteLine(dataTable1.Compute("sum(QTY)","ID>1"));
Console.ReadKey();
}
/// <summary>
/// 初始化DataTable
/// </summary>
/// <returns></returns>
private static DataTable InitDataTable()
{
DataTable dataTable1 = new DataTable();
DataColumn dc = new DataColumn
{
ColumnName = "ID",
Caption = "序号"
};
dataTable1.Columns.Add(dc);
dc = new DataColumn
{
ColumnName = "QTY",
Caption = "数量",
DataType=typeof(decimal)
};
dataTable1.Columns.Add(dc);
DataRow dr = dataTable1.NewRow();
dr["ID"] = 1;
dr["QTY"] = 5;
dataTable1.Rows.Add(dr);
dr = dataTable1.NewRow();
dr["ID"] = 2;
dr["QTY"] = 54;
dataTable1.Rows.Add(dr);
dr = dataTable1.NewRow();
dr["ID"] = 3;
dr["QTY"] = 6;
dataTable1.Rows.Add(dr);
dr = dataTable1.NewRow();
dr["ID"] = 4;
dr["QTY"] = 7;
dataTable1.Rows.Add(dr);
return dataTable1;
}
如果使用两个字段的乘积求和需要提前设定表达式即在创建DataColunm时设定。
dc = new DataColumn
{
ColumnName = "TOTAL",
Caption = "ID*QTY",
DataType = typeof(decimal),
Expression="ID*QTY"
};
dataTable1.Columns.Add(dc);
效果如下：
static void Main(string[] args)
{
var dataTable1= InitDataTable();
Console.WriteLine(dataTable1.Compute("sum(TOTAL)","ID>1"));
Console.ReadKey();
}
/// <summary>
/// 初始化DataTable
/// </summary>
/// <returns></returns>
private static DataTable InitDataTable()
{
DataTable dataTable1 = new DataTable();
DataColumn dc = new DataColumn
{
ColumnName = "ID",
Caption = "序号",
DataType = typeof(decimal)
};
dataTable1.Columns.Add(dc);
dc = new DataColumn
{
ColumnName = "QTY",
Caption = "数量",
DataType=typeof(decimal)
};
dataTable1.Columns.Add(dc);
dc = new DataColumn
{
ColumnName = "TOTAL",
Caption = "ID*QTY",
DataType = typeof(decimal),
Expression="ID*QTY"
};
dataTable1.Columns.Add(dc);
DataRow dr = dataTable1.NewRow();
dr["ID"] = 1;
dr["QTY"] = 5;
dataTable1.Rows.Add(dr);
dr = dataTable1.NewRow();
dr["ID"] = 2;
dr["QTY"] = 54;
dataTable1.Rows.Add(dr);
dr = dataTable1.NewRow();
dr["ID"] = 3;
dr["QTY"] = 6;
dataTable1.Rows.Add(dr);
dr = dataTable1.NewRow();
dr["ID"] = 4;
dr["QTY"] = 7;
dataTable1.Rows.Add(dr);
return dataTable1;
}