How do you deal with DataSet in MVVM?

Question

Since DataSet is somehow a first-class binding source, is there a need to wrap the DataTable into an Object Model? DataTable is already a model representation on its own, do you just need the ViewModel?

Answer 1

You can convert DataTable (DataSet is constructed by one or more DataTables) into ObservableCollection and then bind ObservableCollection to UI element.

For example:

XAML

<Window x:Class="_temple.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"        
        xmlns:local="clr-namespace:_temple"
        xmlns:sys="clr-namespace:System;assembly=mscorlib"
    Width="892" Height="612">
    <Canvas  Background="Azure">
        <ComboBox Canvas.Left="60" Canvas.Top="12" Height="23" Name="ddl" Width="120" SelectionChanged="ddl_SelectionChanged">
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <ComboBoxItem>
                        <Binding></Binding>
                    </ComboBoxItem>
                </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>
        <ListView Canvas.Left="12" Canvas.Top="46" Height="516" Name="MyListView" Width="846" >
            <ListView.View>
                <GridView AllowsColumnReorder="true" >
                    <GridViewColumn Header="Project">
                        <GridViewColumn.CellTemplate>
                            <DataTemplate>
                                <TextBlock Width="30">
                                    <TextBlock.Text>
                                   <Binding   Path="Project"></Binding>
                                        </TextBlock.Text>
                                </TextBlock>
                            </DataTemplate>
                        </GridViewColumn.CellTemplate>
                    </GridViewColumn>
                    <GridViewColumn Width="720" >
                        <GridViewColumn.HeaderTemplate>
                            <DataTemplate>
                                <StackPanel Name="HeaderContainer" Orientation="Horizontal">
                                    <TextBlock Width="23">1</TextBlock>
                                    <TextBlock Width="23">2</TextBlock>
                                    <TextBlock Width="23">3</TextBlock>
                                    <TextBlock Width="23">4</TextBlock>
                                    <TextBlock Width="23">5</TextBlock>
                                    <TextBlock Width="23">6</TextBlock>
                                    <TextBlock Width="23">7</TextBlock>
                                    <TextBlock Width="23">8</TextBlock>
                                    <TextBlock Width="23">9</TextBlock>
                                    <TextBlock Width="23">10</TextBlock>
                                    <TextBlock Width="23">11</TextBlock>
                                    <TextBlock Width="23">12</TextBlock>
                                    <TextBlock Width="23">13</TextBlock>
                                    <TextBlock Width="23">14</TextBlock>
                                    <TextBlock Width="23">15</TextBlock>
                                    <TextBlock Width="23">16</TextBlock>
                                    <TextBlock Width="23">17</TextBlock>
                                    <TextBlock Width="23">18</TextBlock>
                                    <TextBlock Width="23">19</TextBlock>
                                    <TextBlock Width="23">20</TextBlock>
                                    <TextBlock Width="23">21</TextBlock>
                                    <TextBlock Width="23">22</TextBlock>
                                    <TextBlock Width="23">23</TextBlock>
                                    <TextBlock Width="23">24</TextBlock>
                                    <TextBlock Width="23">25</TextBlock>
                                    <TextBlock Width="23">26</TextBlock>
                                    <TextBlock Width="23">27</TextBlock>
                                    <TextBlock Width="23">28</TextBlock>
                                    <TextBlock Width="23">29</TextBlock>
                                    <TextBlock Width="23">30</TextBlock>
                                    <TextBlock Width="23">31</TextBlock>
                                </StackPanel>
                            </DataTemplate>
                        </GridViewColumn.HeaderTemplate>
                        <GridViewColumn.CellTemplate>
                            <DataTemplate>
                                <StackPanel Loaded="MyStackPanel_Loaded"  Name="MyStackPanel"   Orientation="Horizontal">
                                    <StackPanel.Tag>
                                        <Binding></Binding>
                                    </StackPanel.Tag> 
                                </StackPanel> 
                            </DataTemplate>
                        </GridViewColumn.CellTemplate>
                    </GridViewColumn>
                    <GridViewColumn Header="TotalHours">
                        <GridViewColumn.CellTemplate>
                            <DataTemplate>
                                <TextBlock Width="60">
                                    <TextBlock.Text>
                                   <Binding   Path="TotalHours"></Binding>
                                        </TextBlock.Text>
                                </TextBlock>
                            </DataTemplate>
                        </GridViewColumn.CellTemplate>
                    </GridViewColumn>
                </GridView>
            </ListView.View>
        </ListView>
        <Label Canvas.Left="12" Canvas.Top="12" Height="28"  Width="42">User:</Label>
        <Button Canvas.Left="198" Canvas.Top="12" Height="23" Name="btnAddData" Width="75" Click="btnAddData_Click">Add Data</Button>
    </Canvas>
</Window>

C#

using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Collections.ObjectModel;
using System.Data;
using System.Threading;
namespace _temple
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public DataTable data = new DataTable();
        public DataTable dtBind = new DataTable();
        public ObservableCollection<int> UserIDList = new ObservableCollection<int>();
        ObservableCollection<ProjectWorkHours> DataList = new ObservableCollection<ProjectWorkHours>();
        public Window1()
        { 
            InitializeComponent();
            Display();
        }
        public void Display()
        {
            data = new DataTable();
            data.Columns.Add("UserID");
            data.Columns.Add("ProjectID");
            data.Columns.Add("Day");
            data.Columns.Add("Number");
            //add some data
            AddData();
            //Set Bind
            dtBind = data.Copy();
            ConvertDataTable(dtBind); 
            this.MyListView.ItemsSource = DataList;
            //Get all users
            ResetUserList(data);
            //Bind UserList to ComboBox
            ddl.ItemsSource = UserIDList;
            ddl.SelectedIndex =0;
        }
        public void AddData()
        {
            #region
            Random r = new Random();
            for (int i = 1; i <= 10; i++)
            {
                for (int n = 1; n <= 5; n++)
                {
                    for (int j = 0; j < 30; j++)
                    {
                        Thread.Sleep(1); 
                        int randomDay = r.Next(30) + 1;
                        AddRow(i  , n, randomDay, 1);
                    }
                }
            }
            #endregion
        }
        public void ResetUserList( DataTable dt )
        {
            UserIDList.Clear();
            for ( int i = 0 ; i < dt.Rows.Count; i ++ )
            {
                DataRow dr = dt.Rows[i];
                int UserID = int.Parse( dr["UserID"].ToString() );
                if ( !UserIDList.Contains( UserID ) )
                {
                    UserIDList.Add( UserID );
                }
            }
        }
        public void AddRow( int _user, int _pro, int _day, int _num )
        {
            DataRow dr = data.NewRow();
            dr["UserID"] = _user;
            dr["ProjectID"] = _pro;
            dr["Day"] = _day;
            dr["Number"] = _num;
            data.Rows.Add(dr);
        }
        private void ddl_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            RefreshData();
        }
        public void RefreshData()
        {
            //Change the dtBind using Select
            string userid = ddl.SelectedItem.ToString();
            DataRow[] drC = data.Select("UserID='" + userid + "'");
            dtBind.Rows.Clear();
            for (int i = 0; i < drC.Length; i++)
            {
                DataRow dr = dtBind.NewRow();
                DataRow _dr = drC[i];
                dr["UserID"] = _dr["UserID"];
                dr["ProjectID"] = _dr["ProjectID"];
                dr["Day"] = _dr["Day"];
                dr["Number"] = _dr["Number"];
                dtBind.Rows.Add(dr);
            }
            ConvertDataTable(dtBind);
            MyListView.ItemsSource = DataList;
        }
        public void ConvertDataTable( DataTable dt )
        {
            DataList  = new ObservableCollection<ProjectWorkHours>();
            //Scan and arrange data into ObservableCollection
            int UserID = 0;
            if ( dt.Rows.Count >0 )
            {
                UserID = int.Parse( dt.Rows[0]["UserID"].ToString() );
                //Distill project id list
                List<int> ProjectIDList = GetProjectIDList( dt );
                for ( int i = 0 ; i < ProjectIDList.Count; i ++ )
                {
                    int ProjectID= ProjectIDList[i];
                    //Get WorkRecord
                    int[] MyWorkRecord = GetWorkRecord(dt, ProjectID);
                    ProjectWorkHours newProjectWorkHours = new ProjectWorkHours(UserID,ProjectID,MyWorkRecord);
                    DataList.Add( newProjectWorkHours);
                }           
            } 
        }
        public List<int> GetProjectIDList( DataTable dt )
        {
            List<int> ProjectIDList = new List<int>();
            for ( int i = 0 ; i < dt.Rows.Count; i ++ )
            {
                DataRow dr = dt.Rows[i];
                int ProjectID = int.Parse( dr["ProjectID"].ToString() );
                if ( !ProjectIDList.Contains( ProjectID ) )
                {
                    ProjectIDList.Add(ProjectID);
                }
            }
            return ProjectIDList;
        }
        public int[] GetWorkRecord( DataTable dt, int ProjectID )
        {
            int[] MyWorkRecord = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
            //scan the data
            DataRow[]  drScan = dt.Select( " ProjectID='"+ProjectID+"' " );
            for (int i = 0; i < drScan.Length; i++)
            {
                DataRow dr = drScan[i];
                int day = int.Parse( dr["Day"].ToString() );
                int num = int.Parse( dr["Number"].ToString() );
                MyWorkRecord[day-1] += num;
            }
            return MyWorkRecord;
        }
        private void MyStackPanel_Loaded(object sender, RoutedEventArgs e)
        {
            StackPanel MyStackPanel = sender as StackPanel;
            if (MyStackPanel != null)
            {
                MyStackPanel.Children.Clear();
                for (int i = 1; i <= 31; i++)
                {
                    TextBox txt = new TextBox();
                    txt.Width = 23;
                    ProjectWorkHours PW = MyStackPanel.Tag as ProjectWorkHours;
                    if (PW != null)
                    {
                        txt.Text = PW.WorkRecord[i - 1].ToString();
                    }
                    MyStackPanel.Children.Add(txt);
                }
            }
        }
        private void btnAddData_Click(object sender, RoutedEventArgs e)
        {
            Random r = new Random();
            for (int i = 0; i < 4; i++)
            {
                int randomPro = r.Next(4) + 1;
                int randomDay = r.Next(30)+1;
                AddRow(i+1, randomPro, randomDay, 1);
            }
            RefreshData();
        }
    }
    public class ProjectWorkHours
    {
        public int User { set; get; }
        public int Project {set;get;}
        public int[] WorkRecord {set;get;}
        public int TotalHours{set;get;}
        public ProjectWorkHours( int _user, int _proj, int[] _work )
        {
            User = _user;
            Project = _proj;
            WorkRecord = _work;
            TotalHours = SumTotal( _work );
        }
        public int SumTotal( int[] number )
        {
            int result = 0;
            for ( int i = 0 ; i < number.Length; i ++ )
            {
                result += number[i];
            }
            return result;
        }
    }
}

Answer 2

Thanks for the sample code. So there seems to be no need for an actual Model, just a View-Model.  Is that pretty standard? 

Answer 3

The DataTable itself is the Model here, isn't it?

Answer 4

It's a rough Model, but it is a Model. I'm just wondering if it's customary to create a wrapper for the DataTable, or if it is by "need" basis.

Answer 5

By need. Design patterns are a guide, they aren't set in stone. Besides, M-V-VM is supposed to deal with anything you can think of as a Model, some DataTables from a SQL database is a typical scenario, IMHO.

Answer 6

What if you needed to convert that Observable collection back to a dataset so it could be saved?