DataSetHelper 操作dataset 辅助类（2） DataTable中进行Distinct、Group by、Join、Create
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
#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
#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
#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
#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
#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
}
}
调用：
dt = dsHelper.SelectGroupByInto("OrderSummary", ds.Tables["Employees"],
"EmployeeID,sum(Amount) Total,min(Amount) Min,max(Amount) Max", "EmployeeID<5", "EmployeeID");
此调用示例创建新 DataTable 具有四个字段 （EmployeeID、 总计、, Min 和 Max） 以及 OrderSummary TableName 。 这些四个字段具有相同数据类型， EmployeeID 和 Orders 表中数量字段。 然后本示例从 Orders DataTable , 读取记录并将记录写入 OrderSummary DataTable 。 OrderSummary DataTable 包含 EmployeeID 域和三个不同的聚合的金额字段上筛选， EmployeeID EmployeeID 5 和， 是上分组 （和按） < "。 如果 GroupBy 参数是空白, DataTable 目标包含聚合所有输入仅单个记录。
参考地址：http://support.microsoft.com/kb/326145
http://topic.csdn.net/t/20060514/14/4750499.html