关于dataset的认识

 using System;
using System.Collections.Generic;
using System.Data;

namespace Andy.DataSetHelper
public class DataSetHelper
{


       public DataSet ds;

       private System.Collections.ArrayList m_FieldInfo;
       private string m_FieldList;

       public DataSetHelper(ref DataSet DataSet)
       {
           ds = DataSet;
       }
       public DataSetHelper()
       {
           ds = null;
       }
       /** <summary>
       /// 该方法根据给定的字段列表(FieldList)和表名（TableName），创建表结构，并返回表对象
       /// 给定的字段可来自创建了关系的两张表，如果是源表（子表）中的字段，直接写字段名即可。
       /// 如果是关系表（父表）中的字段，
       /// 字段前面须加上关系名称，格式如：relationname.fieldname
       /// FieldList语法：[relationname.]fieldname[ alias][,[relationname.]fieldname[ alias]]
       /// </summary>
       /// <param name="TableName">生成新结构表的表名</param>
       /// <param name="SourceTable">源表名（子表）</param>
       /// <param name="FieldList">生成新结构表的目标字段</param>
       /// <returns>具有目标结构的表对象</returns>
       public DataTable CreateJoinTable(string TableName, DataTable SourceTable, string FieldList)
       {
           if (FieldList == null)
           {
               throw new ArgumentException("You must specify at least one field in the field list.");
           }
           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;
           }
       }
       /** <summary>
       /// 该方法用于关联查询，可以指定条件（RowFilter），以及排序字段（Sort）；
       /// 直接将查询结果存储到DestTable表对象中/n
       /// 在FieldList中的字段可以是关系表中的字段，但是它的前面必须加上关系名称，格式如：relationname.fieldname
       /// 用于指定查询条件的字段和用于排序的字段只能是源表中的字段，不能是关系表中的字段
       /// FieldList语法：[relationname.]fieldname[ alias][,[relationname.]fieldname[ alias]]
       /// </summary>
       /// <param name="DestTable">用于存储查询结果的表对象</param>
       /// <param name="SourceTable">源表名（子表）</param>
       /// <param name="FieldList">查询结果的目标字段</param>
       /// <param name="RowFilter">查询条件</param>
       /// <param name="Sort">排序字段</param>
       public void InsertJoinInto(DataTable DestTable, DataTable SourceTable, string FieldList, string RowFilter, string Sort)
       {
           if (FieldList == null)
           {
               throw new ArgumentException("You must specify at least one field in the field list.");
           }
           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);
                }
            }
        }
        /** <summary>
        /// 1.该方法用于关联查询，可以指定条件（RowFilter），以及排序字段（Sort）；
        /// 2.将查询结果存储到名称为TableName的表对象中；
        /// 3.在FieldList中的字段可以是关系表中的字段，但是它的前面必须加上关系名称，格式如：relationname.fieldname；
        /// 4.用于指定查询条件的字段和用于排序的字段只能是源表中的字段，不能是关系表中的字段；
        /// 5.FieldList语法：[relationname.]fieldname[ alias][,[relationname.]fieldname[ alias]]
        /// </summary>
        /// <param name="TableName">查询结果表名</param>
        /// <param name="SourceTable">源表名（子表）</param>
        /// <param name="FieldList">查询结果的目标字段</param>
        /// <param name="RowFilter">查询条件</param>
        /// <param name="Sort">排序字段</param>
        /// <returns>查询结果对象</returns>
        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;
        }

        private void ParseFieldList(string FieldList, bool AllowRelation)
        {
            /**//*
           * 将FieldList中的字段转换为FieldInfo对象，并添加到集合m_FieldInfo中
           *
           * FieldList 用例: [relationname.]fieldname[ alias],
          */
            if (m_FieldList == FieldList) return;
            m_FieldInfo = new System.Collections.ArrayList();
            m_FieldList = FieldList;
            FieldInfo Field;
            string[] FieldParts;
            string[] Fields = FieldList.Split(',');
            int i;
            for (i = 0; i <= Fields.Length - 1; i++)
            {
                Field = new FieldInfo();
                //转换别名，存储在Field.FieldAlias
                FieldParts = Fields[i].Trim().Split(' ');
                switch (FieldParts.Length)
                {
                    case 1:
                        //没有别名
                        break;
                    case 2:
                        Field.FieldAlias = FieldParts[1];
                        break;
                    default:
                        throw new Exception("Too many spaces in field definition: '" + Fields[i] + "'.");
                }
                //转换字段名称和关系名称，分别存储在Field.FieldName和Field.RelationName中
                FieldParts = FieldParts[0].Split('.');
                switch (FieldParts.Length)
                {
                    case 1:
                        Field.FieldName = FieldParts[0];
                        break;
                    case 2:
                        if (AllowRelation == false)
                            throw new Exception("Relation specifiers not permitted in field list: '" + Fields[i] + "'.");
                        Field.RelationName = FieldParts[0].Trim();
                        Field.FieldName = FieldParts[1].Trim();
                        break;
                    default:
                        throw new Exception("Invalid field definition: " + Fields[i] + "'.");
                }
                if (Field.FieldAlias == null)
                    Field.FieldAlias = Field.FieldName;
                m_FieldInfo.Add(Field);
            }
        }

    }
    class FieldInfo
    {
        public string RelationName;
        public string FieldName;    //源表的字段名；
        public string FieldAlias;    //查询结果表中的字段名，即需要查询字段的别名；
        public string Aggregate;
    }
}
二.使用方法:
1.在项目中添加引用
2.程序中添加命名空间，如：using Andy.DataSetHelper;
3.定义对象，并实例化，如：DataSetHelper dsHelper = new DataSetHelper(ref ds);   ds为需要操作的DataSet对象
4.调用查询方法，如：dsHelper.SelectJoinInto("查询结果表名", ds.Tables["源表名（子表）"], "查询结果的目标字段", "查询条件", "排序字段"); 各参数的说明见前文。
5调用完成后，在ds中将有一张名称为“查询结果表名”的DataTable。
三.使用用例:
定义变量，并初始化
DataSet ds = new DataSet();
DataSetHelper dsHelper = new DataSetHelper(ref ds);
GridView dataGrid1 = new GridView();
//创建第一张表Employees
DataTable dt = new DataTable("Employees");
dt.Columns.Add("EmployeeID",Type.GetType("System.Int32") );
dt.Columns.Add("FirstName", Type.GetType("System.String"));
dt.Columns.Add("LastName", Type.GetType("System.String"));
dt.Columns.Add("BirthDate", Type.GetType("System.DateTime"));
dt.Columns.Add("JobTitle", Type.GetType("System.String"));
dt.Columns.Add("DepartmentID", Type.GetType("System.Int32"));
dt.Rows.Add(new object[] {1, "Tommy", "Hill", new DateTime(1970, 12, 31), "Manager", 42});
dt.Rows.Add(new object[] {2, "Brooke", "Sheals", new DateTime(1977, 12, 31), "Manager", 23});
dt.Rows.Add(new object[] {3, "Bill", "Blast", new DateTime(1982, 5, 6), "Sales Clerk", 42});
ds.Tables.Add(dt); ///添加到ds中
//创建第二张表Departments
dt = new DataTable("Departments");
dt.Columns.Add("DepartmentID", Type.GetType("System.Int32"));
dt.Columns.Add("DepartmentName", Type.GetType("System.String"));
dt.Rows.Add(new object[] {15, "Men's Clothing"});
dt.Rows.Add(new object[] {23, "Women's Clothing"});
dt.Rows.Add(new object[] {42, "Children's Clothing"});
ds.Tables.Add(dt); ///添加到ds中
//添加关系
ds.Relations.Add("DepartmentEmployee", ds.Tables["Departments"].Columns["DepartmentID"], ds.Tables["Employees"].Columns["DepartmentID"]);
///条用方法
dsHelper.SelectJoinInto("EmpDept2", ds.Tables["Employees"], "FirstName,LastName,BirthDate BDate,DepartmentEmployee.DepartmentName Department", "JobTitle='Manager'", "DepartmentID");
绑定结果
dataGrid1.SetDataBinding(ds, "EmpDept2");