DataSetHelper ，可以对DataSet中的DataTable进行Distinct、Group by、Join和Create。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Collections;
using System.Data;

/// <summary>
///DataSetHelper DataSet操作类 liyang 20100407
/// </summary>
public class DataSetHelper
{
private class FieldInfo
{
public string RelationName;
public string FieldName;
public string FieldAlias;
public string Aggregate;
}

private DataSet ds;
private ArrayList m_FieldInfo;
private string m_FieldList;
private ArrayList GroupByFieldInfo;
private string GroupByFieldList;

public DataSet DataSet
{
get { return ds; }
}

// ConstructionConstruction
#region Construction

public DataSetHelper()
{
ds = null;
}

public DataSetHelper(ref DataSet dataSet)
{
ds = dataSet;
}

#endregion

// Private MethodsPrivate Methods
#region Private Methods

private bool ColumnEqual(object objectA, object objectB)
{
if (objectA == DBNull.Value && objectB == DBNull.Value)
{
return true;
}
if (objectA == DBNull.Value || objectB == DBNull.Value)
{
return false;
}
return (objectA.Equals(objectB));
}

private bool RowEqual(DataRow rowA, DataRow rowB, DataColumnCollection columns)
{
bool result = true;
for (int i = 0; i < columns.Count; i++)
{
result &= ColumnEqual(rowA[columns[i].ColumnName], rowB[columns[i].ColumnName]);
}
return result;
}

private void ParseFieldList(string fieldList, bool allowRelation)
{
if (m_FieldList == fieldList)
{
return;
}
m_FieldInfo = new ArrayList();
m_FieldList = fieldList;
FieldInfo Field;
string[] FieldParts;
string[] Fields = fieldList.Split(',');
for (int i = 0; i <= Fields.Length - 1; i++)
{
Field = new FieldInfo();
FieldParts = Fields[i].Trim().Split(' ');
switch (FieldParts.Length)
{
case 1:
//to be set at the end of the loop
break;
case 2:
Field.FieldAlias = FieldParts[1];
break;
default:
return;
}
FieldParts = FieldParts[0].Split('.');
switch (FieldParts.Length)
{
case 1:
Field.FieldName = FieldParts[0];
break;
case 2:
if (allowRelation == false)
{
return;
}
Field.RelationName = FieldParts[0].Trim();
Field.FieldName = FieldParts[1].Trim();
break;
default:
return;
}
if (Field.FieldAlias == null)
{
Field.FieldAlias = Field.FieldName;
}
m_FieldInfo.Add(Field);
}
}

private DataTable CreateTable(string tableName, DataTable sourceTable, string fieldList)
{
DataTable dt;
if (fieldList.Trim() == "")
{
dt = sourceTable.Clone();
dt.TableName = tableName;
}
else
{
dt = new DataTable(tableName);
ParseFieldList(fieldList, false);
DataColumn dc;
foreach (FieldInfo Field in m_FieldInfo)
{
dc = sourceTable.Columns[Field.FieldName];
DataColumn column = new DataColumn();
column.ColumnName = Field.FieldAlias;
column.DataType = dc.DataType;
column.MaxLength = dc.MaxLength;
column.Expression = dc.Expression;
dt.Columns.Add(column);
}
}
if (ds != null)
{
ds.Tables.Add(dt);
}
return dt;
}

private void InsertInto(DataTable destTable, DataTable sourceTable,
string fieldList, string rowFilter, string sort)
{
ParseFieldList(fieldList, false);
DataRow[] rows = sourceTable.Select(rowFilter, sort);
DataRow destRow;
foreach (DataRow sourceRow in rows)
{
destRow = destTable.NewRow();
if (fieldList == "")
{
foreach (DataColumn dc in destRow.Table.Columns)
{
if (dc.Expression == "")
{
destRow[dc] = sourceRow[dc.ColumnName];
}
}
}
else
{
foreach (FieldInfo field in m_FieldInfo)
{
destRow[field.FieldAlias] = sourceRow[field.FieldName];
}
}
destTable.Rows.Add(destRow);
}
}

private void ParseGroupByFieldList(string FieldList)
{
if (GroupByFieldList == FieldList)
{
return;
}
GroupByFieldInfo = new ArrayList();
FieldInfo Field;
string[] FieldParts;
string[] Fields = FieldList.Split(',');
for (int i = 0; i <= Fields.Length - 1; i++)
{
Field = new FieldInfo();
FieldParts = Fields[i].Trim().Split(' ');
switch (FieldParts.Length)
{
case 1:
//to be set at the end of the loop
break;
case 2:
Field.FieldAlias = FieldParts[1];
break;
default:
return;
}

FieldParts = FieldParts[0].Split('(');
switch (FieldParts.Length)
{
case 1:
Field.FieldName = FieldParts[0];
break;
case 2:
Field.Aggregate = FieldParts[0].Trim().ToLower();
Field.FieldName = FieldParts[1].Trim(' ', ')');
break;
default:
return;
}
if (Field.FieldAlias == null)
{
if (Field.Aggregate == null)
{
Field.FieldAlias = Field.FieldName;
}
else
{
Field.FieldAlias = Field.Aggregate + "of" + Field.FieldName;
}
}
GroupByFieldInfo.Add(Field);
}
GroupByFieldList = FieldList;
}

private DataTable CreateGroupByTable(string tableName, DataTable sourceTable, string fieldList)
{
if (fieldList == null || fieldList.Length == 0)
{
return sourceTable.Clone();
}
else
{
DataTable dt = new DataTable(tableName);
ParseGroupByFieldList(fieldList);
foreach (FieldInfo Field in GroupByFieldInfo)
{
DataColumn dc = sourceTable.Columns[Field.FieldName];
if (Field.Aggregate == null)
{
dt.Columns.Add(Field.FieldAlias, dc.DataType, dc.Expression);
}
else
{
dt.Columns.Add(Field.FieldAlias, dc.DataType);
}
}
if (ds != null)
{
ds.Tables.Add(dt);
}
return dt;
}
}

private void InsertGroupByInto(DataTable destTable, DataTable sourceTable, string fieldList,
string rowFilter, string groupBy)
{
if (fieldList == null || fieldList.Length == 0)
{
return;
}
ParseGroupByFieldList(fieldList);
ParseFieldList(groupBy, false);
DataRow[] rows = sourceTable.Select(rowFilter, groupBy);
DataRow lastSourceRow = null, destRow = null;
bool sameRow;
int rowCount = 0;
foreach (DataRow sourceRow in rows)
{
sameRow = false;
if (lastSourceRow != null)
{
sameRow = true;
foreach (FieldInfo Field in m_FieldInfo)
{
if (!ColumnEqual(lastSourceRow[Field.FieldName], sourceRow[Field.FieldName]))
{
sameRow = false;
break;
}
}
if (!sameRow)
{
destTable.Rows.Add(destRow);
}
}
if (!sameRow)
{
destRow = destTable.NewRow();
rowCount = 0;
}
rowCount += 1;
foreach (FieldInfo field in GroupByFieldInfo)
{
switch (field.Aggregate)
{
case null:
case "":
case "last":
destRow[field.FieldAlias] = sourceRow[field.FieldName];
break;
case "first":
if (rowCount == 1)
{
destRow[field.FieldAlias] = sourceRow[field.FieldName];
}
break;
case "count":
destRow[field.FieldAlias] = rowCount;
break;
case "sum":
destRow[field.FieldAlias] = Add(destRow[field.FieldAlias], sourceRow[field.FieldName]);
break;
case "max":
destRow[field.FieldAlias] = Max(destRow[field.FieldAlias], sourceRow[field.FieldName]);
break;
case "min":
if (rowCount == 1)
{
destRow[field.FieldAlias] = sourceRow[field.FieldName];
}
else
{
destRow[field.FieldAlias] = Min(destRow[field.FieldAlias], sourceRow[field.FieldName]);
}
break;
}
}
lastSourceRow = sourceRow;
}
if (destRow != null)
{
destTable.Rows.Add(destRow);
}
}

private object Min(object a, object b)
{
if ((a is DBNull) || (b is DBNull))
{
return DBNull.Value;
}
if (((IComparable)a).CompareTo(b) == -1)
{
return a;
}
else
{
return b;
}
}

private object Max(object a, object b)
{
if (a is DBNull)
{
return b;
}
if (b is DBNull)
{
return a;
}
if (((IComparable)a).CompareTo(b) == 1)
{
return a;
}
else
{
return b;
}
}

private object Add(object a, object b)
{
if (a is DBNull)
{
return b;
}
if (b is DBNull)
{
return a;
}
return ((decimal)a + (decimal)b);
}

private DataTable CreateJoinTable(string tableName, DataTable sourceTable, string fieldList)
{
if (fieldList == null)
{
return sourceTable.Clone();
}
else
{
DataTable dt = new DataTable(tableName);
ParseFieldList(fieldList, true);
foreach (FieldInfo field in m_FieldInfo)
{
if (field.RelationName == null)
{
DataColumn dc = sourceTable.Columns[field.FieldName];
dt.Columns.Add(dc.ColumnName, dc.DataType, dc.Expression);
}
else
{
DataColumn dc = sourceTable.ParentRelations[field.RelationName].ParentTable.Columns[field.FieldName];
dt.Columns.Add(dc.ColumnName, dc.DataType, dc.Expression);
}
}
if (ds != null)
{
ds.Tables.Add(dt);
}
return dt;
}
}

private void InsertJoinInto(DataTable destTable, DataTable sourceTable,
string fieldList, string rowFilter, string sort)
{
if (fieldList == null)
{
return;
}
else
{
ParseFieldList(fieldList, true);
DataRow[] Rows = sourceTable.Select(rowFilter, sort);
foreach (DataRow SourceRow in Rows)
{
DataRow DestRow = destTable.NewRow();
foreach (FieldInfo Field in m_FieldInfo)
{
if (Field.RelationName == null)
{
DestRow[Field.FieldName] = SourceRow[Field.FieldName];
}
else
{
DataRow ParentRow = SourceRow.GetParentRow(Field.RelationName);
DestRow[Field.FieldName] = ParentRow[Field.FieldName];
}
}
destTable.Rows.Add(DestRow);
}
}
}

#endregion

//SelectDistinct / DistinctSelectDistinct / Distinct#region SelectDistinct / Distinct

/**/
/**/
/**/
/// <summary>
/// 按照fieldName从sourceTable中选择出不重复的行，
/// 相当于select distinct fieldName from sourceTable
/// </summary>
/// <param name="tableName">表名</param>
/// <param name="sourceTable">源DataTable</param>
/// <param name="fieldName">列名</param>
/// <returns>一个新的不含重复行的DataTable，列只包括fieldName指明的列</returns>
public DataTable SelectDistinct(string tableName, DataTable sourceTable, string fieldName)
{
DataTable dt = new DataTable(tableName);
dt.Columns.Add(fieldName, sourceTable.Columns[fieldName].DataType);

object lastValue = null;
foreach (DataRow dr in sourceTable.Select("", fieldName))
{
if (lastValue == null || !(ColumnEqual(lastValue, dr[fieldName])))
{
lastValue = dr[fieldName];
dt.Rows.Add(new object[] { lastValue });
}
}
if (ds != null && !ds.Tables.Contains(tableName))
{
ds.Tables.Add(dt);
}
return dt;
}

/**/
/**/
/**/
/// <summary>
/// 按照fieldName从sourceTable中选择出不重复的行，
/// 相当于select distinct fieldName1,fieldName2,,fieldNamen from sourceTable
/// </summary>
/// <param name="tableName">表名</param>
/// <param name="sourceTable">源DataTable</param>
/// <param name="fieldNames">列名数组</param>
/// <returns>一个新的不含重复行的DataTable，列只包括fieldNames中指明的列</returns>
public DataTable SelectDistinct(string tableName, DataTable sourceTable, string[] fieldNames)
{
DataTable dt = new DataTable(tableName);
object[] values = new object[fieldNames.Length];
string fields = "";
for (int i = 0; i < fieldNames.Length; i++)
{
dt.Columns.Add(fieldNames[i], sourceTable.Columns[fieldNames[i]].DataType);
fields += fieldNames[i] + ",";
}
fields = fields.Remove(fields.Length - 1, 1);
DataRow lastRow = null;
foreach (DataRow dr in sourceTable.Select("", fields))
{
if (lastRow == null || !(RowEqual(lastRow, dr, dt.Columns)))
{
lastRow = dr;
for (int i = 0; i < fieldNames.Length; i++)
{
values[i] = dr[fieldNames[i]];
}
dt.Rows.Add(values);
}
}
if (ds != null && !ds.Tables.Contains(tableName))
{
ds.Tables.Add(dt);
}
return dt;
}

/**/
/**/
/**/
/// <summary>
/// 按照fieldName从sourceTable中选择出不重复的行，
/// 并且包含sourceTable中所有的列。
/// </summary>
/// <param name="tableName">表名</param>
/// <param name="sourceTable">源表</param>
/// <param name="fieldName">字段</param>
/// <returns>一个新的不含重复行的DataTable</returns>
public DataTable Distinct(string tableName, DataTable sourceTable, string fieldName)
{
DataTable dt = sourceTable.Clone();
dt.TableName = tableName;

object lastValue = null;
foreach (DataRow dr in sourceTable.Select("", fieldName))
{
if (lastValue == null || !(ColumnEqual(lastValue, dr[fieldName])))
{
lastValue = dr[fieldName];
dt.Rows.Add(dr.ItemArray);
}
}
if (ds != null && !ds.Tables.Contains(tableName))
{
ds.Tables.Add(dt);
}
return dt;
}

/**/
/**/
/**/
/// <summary>
/// 按照fieldNames从sourceTable中选择出不重复的行，
/// 并且包含sourceTable中所有的列。
/// </summary>
/// <param name="tableName">表名</param>
/// <param name="sourceTable">源表</param>
/// <param name="fieldNames">字段</param>
/// <returns>一个新的不含重复行的DataTable</returns>
public DataTable Distinct(string tableName, DataTable sourceTable, string[] fieldNames)
{
DataTable dt = sourceTable.Clone();
dt.TableName = tableName;
string fields = "";
for (int i = 0; i < fieldNames.Length; i++)
{
fields += fieldNames[i] + ",";
}
fields = fields.Remove(fields.Length - 1, 1);
DataRow lastRow = null;
foreach (DataRow dr in sourceTable.Select("", fields))
{
if (lastRow == null || !(RowEqual(lastRow, dr, dt.Columns)))
{
lastRow = dr;
dt.Rows.Add(dr.ItemArray);
}
}
if (ds != null && !ds.Tables.Contains(tableName))
{
ds.Tables.Add(dt);
}
return dt;
}

// #endregion

//Select Table IntoSelect Table Into
#region Select Table Into

/**/
/**/
/**/
/// <summary>
/// 按sort排序，按rowFilter过滤sourceTable，
/// 复制fieldList中指明的字段的数据到新DataTable，并返回之
/// </summary>
/// <param name="tableName">表名</param>
/// <param name="sourceTable">源表</param>
/// <param name="fieldList">字段列表</param>
/// <param name="rowFilter">过滤条件</param>
/// <param name="sort">排序</param>
/// <returns>新DataTable</returns>
public DataTable SelectInto(string tableName, DataTable sourceTable,
string fieldList, string rowFilter, string sort)
{
DataTable dt = CreateTable(tableName, sourceTable, fieldList);
InsertInto(dt, sourceTable, fieldList, rowFilter, sort);
return dt;
}

#endregion

//Group By TableGroup By Table
#region Group By Table

public DataTable SelectGroupByInto(string tableName, DataTable sourceTable, string fieldList,
string rowFilter, string groupBy)
{
DataTable dt = CreateGroupByTable(tableName, sourceTable, fieldList);
InsertGroupByInto(dt, sourceTable, fieldList, rowFilter, groupBy);
return dt;
}

#endregion

//Join TablesJoin Tables
#region Join Tables

public DataTable SelectJoinInto(string tableName, DataTable sourceTable, string fieldList, string rowFilter, string sort)
{
DataTable dt = CreateJoinTable(tableName, sourceTable, fieldList);
InsertJoinInto(dt, sourceTable, fieldList, rowFilter, sort);
return dt;
}

#endregion

//Create TableCreate Table
#region Create Table

public DataTable CreateTable(string tableName, string fieldList)
{
DataTable dt = new DataTable(tableName);
DataColumn dc;
string[] Fields = fieldList.Split(',');
string[] FieldsParts;
string Expression;
foreach (string Field in Fields)
{
FieldsParts = Field.Trim().Split(" ".ToCharArray(), 3); // allow for spaces in the expression
// add fieldname and datatype
if (FieldsParts.Length == 2)
{
dc = dt.Columns.Add(FieldsParts[0].Trim(), Type.GetType("System." + FieldsParts[1].Trim(), true, true));
dc.AllowDBNull = true;
}
else if (FieldsParts.Length == 3) // add fieldname, datatype, and expression
{
Expression = FieldsParts[2].Trim();
if (Expression.ToUpper() == "REQUIRED")
{
dc = dt.Columns.Add(FieldsParts[0].Trim(), Type.GetType("System." + FieldsParts[1].Trim(), true, true));
dc.AllowDBNull = false;
}
else
{
dc = dt.Columns.Add(FieldsParts[0].Trim(), Type.GetType("System." + FieldsParts[1].Trim(), true, true), Expression);
}
}
else
{
return null;
}
}
if (ds != null)
{
ds.Tables.Add(dt);
}
return dt;
}

public DataTable CreateTable(string tableName, string fieldList, string keyFieldList)
{
DataTable dt = CreateTable(tableName, fieldList);
string[] KeyFields = keyFieldList.Split(',');
if (KeyFields.Length > 0)
{
DataColumn[] KeyFieldColumns = new DataColumn[KeyFields.Length];
int i;
for (i = 1; i == KeyFields.Length - 1; ++i)
{
KeyFieldColumns[i] = dt.Columns[KeyFields[i].Trim()];
}
dt.PrimaryKey = KeyFieldColumns;
}
return dt;
}

#endregion
}