[DefaultValue(DropDownDirection.Down)]
[Parameter]
public DropDownDirection DropDownDirection { get; set; }

@inject IDbContextFactory<NorthwindContext> NorthwindContextFactory

<DxGrid Data="Products"
        EditMode="GridEditMode.EditRow">
    <Columns>
        <DxGridCommandColumn />
        <DxGridDataColumn FieldName="CategoryId" Caption="Category">
            <EditSettings>
                <DxComboBoxSettings Data="Categories"
                                    ValueFieldName="CategoryId"
                                    TextFieldName="CategoryName"
                                    DropDownDirection="DropDownDirection.Up" />
            </EditSettings>
        </DxGridDataColumn>
        <DxGridDataColumn FieldName="ProductName" Width="25%" />
        <DxGridDataColumn FieldName="UnitPrice" />
        <DxGridDataColumn FieldName="UnitsInStock" />
        <DxGridDataColumn FieldName="QuantityPerUnit" />
    </Columns>
</DxGrid>

@code {
    NorthwindContext Northwind { get; set; }
    List<Product> Products { get; set; }
    List<Category> Categories { get; set; }

    protected override async Task OnInitializedAsync() {
        Northwind = NorthwindContextFactory.CreateDbContext();
        Products = await Northwind.Products.ToListAsync();
        Categories = await Northwind.Categories.ToListAsync();
    }

    public void Dispose() {
        Northwind?.Dispose();
    }
}

using Microsoft.EntityFrameworkCore;
#nullable disable

namespace Grid.Northwind {
    public partial class NorthwindContext : DbContext {

        public NorthwindContext(DbContextOptions<NorthwindContext> options)
            : base(options) {
        }
        // ...
        public virtual DbSet<Category> Categories { get; set; }
        public virtual DbSet<Product> Products { get; set; }
        // ...
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) {
            if(!optionsBuilder.IsConfigured) {
                optionsBuilder.UseSqlServer("Server=.\\sqlexpress;Database=Northwind;Integrated Security=true");
            }
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder) {
            modelBuilder.HasAnnotation("Relational:Collation", "SQL_Latin1_General_CP1_CI_AS");
            // ...
            modelBuilder.Entity<Category>(entity => {
                entity.HasIndex(e => e.CategoryName, "CategoryName");
                entity.Property(e => e.CategoryId).HasColumnName("CategoryID");
                entity.Property(e => e.CategoryName)
                    .IsRequired()
                    .HasMaxLength(15);
                entity.Property(e => e.Description).HasColumnType("ntext");
                entity.Property(e => e.Picture).HasColumnType("image");
            });
            modelBuilder.Entity<Product>(entity => {
                entity.HasIndex(e => e.CategoryId, "CategoriesProducts");
                entity.HasIndex(e => e.CategoryId, "CategoryID");
                entity.HasIndex(e => e.ProductName, "ProductName");
                entity.HasIndex(e => e.SupplierId, "SupplierID");
                entity.HasIndex(e => e.SupplierId, "SuppliersProducts");
                entity.Property(e => e.ProductId).HasColumnName("ProductID");
                entity.Property(e => e.CategoryId).HasColumnName("CategoryID");
                entity.Property(e => e.ProductName)
                    .IsRequired()
                    .HasMaxLength(40);
                entity.Property(e => e.QuantityPerUnit).HasMaxLength(20);
                entity.Property(e => e.ReorderLevel).HasDefaultValueSql("((0))");
                entity.Property(e => e.SupplierId).HasColumnName("SupplierID");
                entity.Property(e => e.UnitPrice)
                    .HasColumnType("money")
                    .HasDefaultValueSql("((0))");
                entity.Property(e => e.UnitsInStock).HasDefaultValueSql("((0))");
                entity.Property(e => e.UnitsOnOrder).HasDefaultValueSql("((0))");
                entity.HasOne(d => d.Category)
                    .WithMany(p => p.Products)
                    .HasForeignKey(d => d.CategoryId)
                    .HasConstraintName("FK_Products_Categories");
            });
            // ...
            OnModelCreatingPartial(modelBuilder);
        }

        partial void OnModelCreatingPartial(ModelBuilder modelBuilder);
    }
}

public partial class Product {
    public Product() {
        OrderDetails = new HashSet<OrderDetail>();
    }

    public int ProductId { get; set; }
    public string ProductName { get; set; }
    public int? SupplierId { get; set; }
    public int? CategoryId { get; set; }
    public string QuantityPerUnit { get; set; }
    public decimal? UnitPrice { get; set; }
    public short? UnitsInStock { get; set; }
    public short? UnitsOnOrder { get; set; }
    public short? ReorderLevel { get; set; }
    public bool Discontinued { get; set; }

    public virtual Category Category { get; set; }
}

public partial class Category {
    public Category() {
        Products = new HashSet<Product>();
    }

    public int CategoryId { get; set; }
    public string CategoryName { get; set; }
    public string Description { get; set; }
    public byte[] Picture { get; set; }

    public virtual ICollection<Product> Products { get; set; }
}