how to select a row on a table based on a condition in another row of another table?

Question

I want to show only the rows from one table that meet a certain condition in another table. Example on the controller :

        using(inventarioEntitiesDBA dc = new inventarioEntitiesDBA())
        {
            ProductandBodViewModel finalitem = new ProductandBodViewModel();

            var m_List = dc.showcase.Where(x => x.prod_on_showcase > 0).ToList();
        }

With the code above it's possible to display only the items that meets the condition, prod_on_showcase > 0 . The ProductandBodViewModel is a model that I created to show two models on a same view.

The ProductandBodViewModel model:

public class ProductandBodViewModel
{
    public List<inventory> inventory { get; set; }

    public List<showcase> showcase { get; set; }
}

According to this condition ( prod_on_showcase > 0 ) I want to show other information that is related to the table showcase table.

The model of the showcase table:

public class showcaseViewModel
{
    public int id_inventory { get; set; }
    
    public int prod_on_showcase { get; set; }
}

The model of the inventory table:

public partial class inventory
{
    public int id_inventory { get; set; }
    public Nullable<int> prod_on_inventory { get; set; }
    public string prod_code { get; set; }
}

The relation between the tables is the id_inventory field.

In this case, the items displayed for the showcase table are 3, so the inventory table must also display 3 items. With the code below it's possible to display info of the table showcase that meets the condition but with the other table ( inventory ) only display the first element that it's found according to the condition prod_on_showcase > 0 .

using(inventarioEntitiesDBA dc = new inventarioEntitiesDBA())
{
    ProductandBodViewModel finalitem = new ProductandBodViewModel();

    var m_List = dc.showcase.Where(x => x.prod_on_showcase > 0).ToList();

    var m_Each = dc.showcase.Where(e => e.prod_on_showcase > 0).Count();

    for(int i = 0; i < m_Each; i++)
    {
        var prodEach = dc.inventory.Where(x => x.prod_on_showcase > 0).FirstOrDefault();

        var b = dc.inventory.Where(a => a.id_inventory == prodEach.id_inventory).ToList();

        finalitem.bod = b;
    }

    finalitem.showcase = m_List;

    return View(finalitem);                
 }

Answer 1

You're asking var prodEach = dc.inventory.Where(x => x.prod_on_showcase > 0).FirstOrDefault(); to always return the First(or default) element in the array.

Linq's SelectMany is useful for what you're trying to do.

using(inventarioEntitiesDBA dc = new inventarioEntitiesDBA())
{
    ProductandBodViewModel finalitem = new ProductandBodViewModel();

    var m_List = dc.showcase.Where(x => x. > 0).ToList();

    var m_List = showcase.Where(x => x.prod_on_showcase > 0).ToList();

    finalitem.showcase = m_List.SelectMany(prodEach
        => dc.inventory.Where(a => a.id_inventory == prodEach.id_inventory)

    finalitem.showcase = m_List;

    return View(finalitem);                
 }```