Question

I’m writing a simple first app using Winforms, C#, VS2010, and Entity Framework. Basically, I have a rich DB I’m tapping, and I’ve already set up the framework, successfully enough to populate a DataGridView control with a subset of the Work Order table.

Now, I want to place a combo box on the form (“cbProjectID”) whose value is ProjectID and DisplayValue is ProjectNbr. I only want to put projects in the combo box list that are related to WorkOrders, and only unique ProjectIDs within that set (a project may have dozens of work orders….)

I’m assuming I need to generate a list from EF, using LINQ. I’m pretty new at LINQ, and I’m not figuring it out…Here’s my code so far…

using System;
using CPASEntityFramework;
using System.Data.Entity;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace BrowseWorkOrders
{
    public partial class BrowseWOs : Form
    {
        public BrowseWOs()
        {
            InitializeComponent();
        }

        private void BrowseWOs_Load(object sender, EventArgs e)
        {
            var context = new CPASEntities();
            var query = context.tblWorkOrders.Where(c => c.ProjectID==8);
            tblWorkOrderBindingSource.DataSource = query.ToList();

        //  Now, I want to load up the Combo Box with all the projects in the Work Order Table

        }
    }
}

I’ve been through the net trying to find a method I understand, but I’m failing. Perhaps someone can help me out. Here’s my Datasource (I assume I should NOT use tblProject, but instead use the tblProject inside tblWorkOrder in order to get my subset…)

Any help and/or guidance would be appreciated.

---

Here’s the code now…

namespace BrowseWorkOrders
{
    public partial class BrowseWOs : Form
    {
        public BrowseWOs()
        {
            InitializeComponent();
        }

        private void BrowseWOs_Load(object sender, EventArgs e)
        {
            // Following loads up all Projects into the cbProjectID Combo Box

            var context = new CPASEntities();
            var PrID = context.qryProjectIDNbrDescs.ToList();
            cbProjectID.DataSource = PrID;
            cbProjectID.ValueMember = "ID";
            cbProjectID.DisplayMember = "ProjectNbr";
        }

        private void cbProjectID_SelectedIndexChanged(object sender, EventArgs e)
        {
            var context = new CPASEntities();
            var query = context.tblWorkOrders.Where(c => c.ProjectID == (int)cbProjectID.SelectedValue).ToList();
            tblWorkOrderBindingSource.DataSource = query;
        }
    }
}

Answer 1

You need the tblProject on the top because the other is for a single WorkOrder only. However, you need to filter the list with those who have at least on WorkOrder:

var projects = context.tblProjects.Where(p => p.tblWorkOrders.Any()).ToArray();
cbProjectID.DataSource = projects;
cbProjectID.ValueMember = "ProjectID";
cbProjectID.DisplayMember = "ProjectNbr";