如果筛选器值为空，则实体框架核心返回所有数据

using System;
using System.Linq;
using Microsoft.EntityFrameworkCore;

// 定义实体类
public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
}

// 定义数据库上下文
public class AppDbContext : DbContext
{
    public DbSet<Product> Products { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer("连接字符串"); // 替换为实际的数据库连接字符串
    }
}

public class Program
{
    public static void Main()
    {
        using (var context = new AppDbContext())
        {
            var products = context.Products.ToList(); // 获取所有产品数据
            foreach (var product in products)
            {
                Console.WriteLine($"ID: {product.Id}, Name: {product.Name}, Price: {product.Price}");
            }
        }
    }
}