SF_10.1, SF_10.2, SF_11.0, SF_11.1, SF_11.2, SF_12.0, SF_12.1, SF_12.2, SF_13.0, SF_13.1, SF_13.2, SF_13.3, SF_14.0, SF_14.1, SF_14.2, SF_14.3 - https://docs.sitefinity.com/for-developers-query-products-by-department

GetProductsByDepartment.cs

using System;
using System.Linq;
using Telerik.OpenAccess;
using Telerik.Sitefinity.Ecommerce.Catalog.Model;
using Telerik.Sitefinity.Model;
using Telerik.Sitefinity.Modules.Ecommerce.Catalog;

namespace Telerik.Sitefinity.Documentation.CodeSnippets.SitefinityEssentials.Modules.Ecommerce.Products
{
    public partial class ProductsCodeSnippets
    {
        public static IQueryable<Product> GetProductsByDepartment(Guid departmentId)
        {
            CatalogManager catalogManager = CatalogManager.GetManager();

            // Get all products that assigned to this department
            IQueryable<Product> productsInDepartment = catalogManager.GetProducts()
                .Where(p => p.GetValue<TrackedList<Guid>>("Department").Contains(departmentId));

            return productsInDepartment;
        }
    }
}