public int GetGroupCount()

@using Microsoft.EntityFrameworkCore
@inject IDbContextFactory<NorthwindContext> NorthwindContextFactory
@implements IDisposable

<DxGrid Data="GridDataSource"
        ShowGroupPanel="true"
        CustomizeCellDisplayText="OnCustomizeCellDisplayText"
        @ref="@MyGrid">
    <Columns>
        <DxGridDataColumn FieldName="OrderDate"
                      DisplayFormat="d"
                      GroupIndex="0"
                      GroupInterval="GridColumnGroupInterval.DateMonth" />
        <DxGridDataColumn FieldName="Customer"
                      SortMode="GridColumnSortMode.DisplayText"
                      GroupIndex="1"
                      GroupInterval="GridColumnGroupInterval.DisplayText" />
        <DxGridDataColumn FieldName="Freight"
                      DisplayFormat="n2" />
    </Columns>
</DxGrid>

<DxButton Click="@OnGetGroupCount">Get Group Count</DxButton>

@Alert

@code {
    IGrid MyGrid { get; set; }
    object GridDataSource { get; set; }
    NorthwindContext Northwind { get; set; }
    public string Alert { get; set; } = "";
    int count;

    protected override void OnInitialized() {
        Northwind = NorthwindContextFactory.CreateDbContext();
        GridDataSource = Northwind.Orders
            .Include(i => i.Customer)
            .Include(i => i.OrderDetails)
            .Include(i => i.ShipViaNavigation)
            .ToList();
    }

    void OnCustomizeCellDisplayText(GridCustomizeCellDisplayTextEventArgs e) {
        if (e.FieldName == "Customer") {
            var customer = (Customer)e.Value;
            e.DisplayText = $"{customer.CompanyName} ({customer.Country}, {customer.City})";
        }
    }

    void OnGetGroupCount() {
        count = MyGrid.GetGroupCount();
        Alert = "The group count equals " + count;
    }

    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<Customer> Customers { get; set; }
        public virtual DbSet<Invoice> Invoices { get; set; }
        public virtual DbSet<Order> Orders { get; set; }
        public virtual DbSet<OrderDetail> OrderDetails { get; set; }
        public virtual DbSet<Product> Products { get; set; }
        public virtual DbSet<Shipper> Shippers { get; set; }
        public virtual DbSet<Supplier> Suppliers { get; set; }
        public virtual DbSet<Employee> Employees { 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<Customer>(entity => {
                entity.HasIndex(e => e.City, "City");
                entity.HasIndex(e => e.CompanyName, "CompanyName");
                entity.HasIndex(e => e.PostalCode, "PostalCode");
                entity.HasIndex(e => e.Region, "Region");
                entity.Property(e => e.CustomerId)
                    .HasMaxLength(5)
                    .HasColumnName("CustomerID")
                    .IsFixedLength(true);
                entity.Property(e => e.Address).HasMaxLength(60);
                entity.Property(e => e.City).HasMaxLength(15);
                entity.Property(e => e.CompanyName)
                    .IsRequired()
                    .HasMaxLength(40);
                entity.Property(e => e.ContactName).HasMaxLength(30);
                entity.Property(e => e.ContactTitle).HasMaxLength(30);
                entity.Property(e => e.Country).HasMaxLength(15);
                entity.Property(e => e.Fax).HasMaxLength(24);
                entity.Property(e => e.Phone).HasMaxLength(24);
                entity.Property(e => e.PostalCode).HasMaxLength(10);
                entity.Property(e => e.Region).HasMaxLength(15);
            });
            modelBuilder.Entity<Invoice>(entity => {
                entity.HasNoKey();
                entity.ToView("Invoices");
                entity.Property(e => e.Address).HasMaxLength(60);
                entity.Property(e => e.City).HasMaxLength(15);
                entity.Property(e => e.Country).HasMaxLength(15);
                entity.Property(e => e.CustomerId)
                    .HasMaxLength(5)
                    .HasColumnName("CustomerID")
                    .IsFixedLength(true);
                entity.Property(e => e.CustomerName)
                    .IsRequired()
                    .HasMaxLength(40);
                entity.Property(e => e.ExtendedPrice).HasColumnType("money");
                entity.Property(e => e.Freight).HasColumnType("money");
                entity.Property(e => e.OrderDate).HasColumnType("datetime");
                entity.Property(e => e.OrderId).HasColumnName("OrderID");
                entity.Property(e => e.PostalCode).HasMaxLength(10);
                entity.Property(e => e.ProductId).HasColumnName("ProductID");
                entity.Property(e => e.ProductName)
                    .IsRequired()
                    .HasMaxLength(40);
                entity.Property(e => e.Region).HasMaxLength(15);
                entity.Property(e => e.RequiredDate).HasColumnType("datetime");
                entity.Property(e => e.Salesperson)
                    .IsRequired()
                    .HasMaxLength(31);
                entity.Property(e => e.ShipAddress).HasMaxLength(60);
                entity.Property(e => e.ShipCity).HasMaxLength(15);
                entity.Property(e => e.ShipCountry).HasMaxLength(15);
                entity.Property(e => e.ShipName).HasMaxLength(40);
                entity.Property(e => e.ShipPostalCode).HasMaxLength(10);
                entity.Property(e => e.ShipRegion).HasMaxLength(15);
                entity.Property(e => e.ShippedDate).HasColumnType("datetime");
                entity.Property(e => e.ShipperName)
                    .IsRequired()
                    .HasMaxLength(40);
                entity.Property(e => e.UnitPrice).HasColumnType("money");
            });
            modelBuilder.Entity<Order>(entity => {
                entity.HasIndex(e => e.CustomerId, "CustomerID");
                entity.HasIndex(e => e.CustomerId, "CustomersOrders");
                entity.HasIndex(e => e.EmployeeId, "EmployeeID");
                entity.HasIndex(e => e.EmployeeId, "EmployeesOrders");
                entity.HasIndex(e => e.OrderDate, "OrderDate");
                entity.HasIndex(e => e.ShipPostalCode, "ShipPostalCode");
                entity.HasIndex(e => e.ShippedDate, "ShippedDate");
                entity.HasIndex(e => e.ShipVia, "ShippersOrders");
                entity.Property(e => e.OrderId).HasColumnName("OrderID");
                entity.Property(e => e.CustomerId)
                    .HasMaxLength(5)
                    .HasColumnName("CustomerID")
                    .IsFixedLength(true);
                entity.Property(e => e.EmployeeId).HasColumnName("EmployeeID");
                entity.Property(e => e.Freight)
                    .HasColumnType("money")
                    .HasDefaultValueSql("((0))");
                entity.Property(e => e.OrderDate).HasColumnType("datetime");
                entity.Property(e => e.RequiredDate).HasColumnType("datetime");
                entity.Property(e => e.ShipAddress).HasMaxLength(60);
                entity.Property(e => e.ShipCity).HasMaxLength(15);
                entity.Property(e => e.ShipCountry).HasMaxLength(15);
                entity.Property(e => e.ShipName).HasMaxLength(40);
                entity.Property(e => e.ShipPostalCode).HasMaxLength(10);
                entity.Property(e => e.ShipRegion).HasMaxLength(15);
                entity.Property(e => e.ShippedDate).HasColumnType("datetime");
                entity.HasOne(d => d.Customer)
                    .WithMany(p => p.Orders)
                    .HasForeignKey(d => d.CustomerId)
                    .HasConstraintName("FK_Orders_Customers");
                entity.HasOne(d => d.ShipViaNavigation)
                    .WithMany(p => p.Orders)
                    .HasForeignKey(d => d.ShipVia)
                    .HasConstraintName("FK_Orders_Shippers");
            });
            modelBuilder.Entity<OrderDetail>(entity => {
                entity.HasKey(e => new { e.OrderId, e.ProductId })
                    .HasName("PK_Order_Details");
                entity.ToTable("Order Details");
                entity.HasIndex(e => e.OrderId, "OrderID");
                entity.HasIndex(e => e.OrderId, "OrdersOrder_Details");
                entity.HasIndex(e => e.ProductId, "ProductID");
                entity.HasIndex(e => e.ProductId, "ProductsOrder_Details");
                entity.Property(e => e.OrderId).HasColumnName("OrderID");
                entity.Property(e => e.ProductId).HasColumnName("ProductID");
                entity.Property(e => e.Quantity).HasDefaultValueSql("((1))");
                entity.Property(e => e.UnitPrice).HasColumnType("money");
                entity.HasOne(d => d.Order)
                    .WithMany(p => p.OrderDetails)
                    .HasForeignKey(d => d.OrderId)
                    .OnDelete(DeleteBehavior.ClientSetNull)
                    .HasConstraintName("FK_Order_Details_Orders");
                entity.HasOne(d => d.Product)
                    .WithMany(p => p.OrderDetails)
                    .HasForeignKey(d => d.ProductId)
                    .OnDelete(DeleteBehavior.ClientSetNull)
                    .HasConstraintName("FK_Order_Details_Products");
            });
            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");
                entity.HasOne(d => d.Supplier)
                    .WithMany(p => p.Products)
                    .HasForeignKey(d => d.SupplierId)
                    .HasConstraintName("FK_Products_Suppliers");
            });
            modelBuilder.Entity<Shipper>(entity => {
                entity.Property(e => e.ShipperId).HasColumnName("ShipperID");
                entity.Property(e => e.CompanyName)
                    .IsRequired()
                    .HasMaxLength(40);
                entity.Property(e => e.Phone).HasMaxLength(24);
            });
            modelBuilder.Entity<Supplier>(entity => {
                entity.HasIndex(e => e.CompanyName, "CompanyName");
                entity.HasIndex(e => e.PostalCode, "PostalCode");
                entity.Property(e => e.SupplierId).HasColumnName("SupplierID");
                entity.Property(e => e.Address).HasMaxLength(60);
                entity.Property(e => e.City).HasMaxLength(15);
                entity.Property(e => e.CompanyName)
                    .IsRequired()
                    .HasMaxLength(40);
                entity.Property(e => e.ContactName).HasMaxLength(30);
                entity.Property(e => e.ContactTitle).HasMaxLength(30);
                entity.Property(e => e.Country).HasMaxLength(15);
                entity.Property(e => e.Fax).HasMaxLength(24);
                entity.Property(e => e.HomePage).HasColumnType("ntext");
                entity.Property(e => e.Phone).HasMaxLength(24);
                entity.Property(e => e.PostalCode).HasMaxLength(10);
                entity.Property(e => e.Region).HasMaxLength(15);
            });
            modelBuilder.Entity<Employee>(entity => {
                entity.HasIndex(e => e.EmployeeId, "EmployeeId");
                entity.HasIndex(e => e.LastName, "LastName");
                entity.HasIndex(e => e.FirstName, "FirstName");
                entity.HasIndex(e => e.Title, "Title");
                entity.HasIndex(e => e.BirthDate, "BirthDate");
                entity.HasIndex(e => e.HireDate, "HireDate");
                entity.HasIndex(e => e.Notes, "Notes");
            });
            OnModelCreatingPartial(modelBuilder);
        }

        partial void OnModelCreatingPartial(ModelBuilder modelBuilder);
    }
}

using Microsoft.EntityFrameworkCore;
// ...
builder.Services.AddDbContextFactory<NorthwindContext>((sp, options) => {
    var env = sp.GetRequiredService<IWebHostEnvironment>();
    var dbPath = Path.Combine(env.ContentRootPath, "Northwind-5e44b51f.mdf");
    options.UseSqlServer("Server=(localdb)\\MSSQLLocalDB;Integrated Security=true;AttachDbFileName=" + dbPath);
});