C#实体框架核心，左连接中的内部选择

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

public class RightTable
{
    public int Id { get; set; }
    public string Description { get; set; }
}

// 创建数据库上下文类
public class MyDbContext : DbContext
{
    public DbSet<LeftTable> LeftTables { get; set; }
    public DbSet<RightTable> RightTables { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer("YourConnectionString");
    }
}

// 执行左连接中的内部选择
using (var context = new MyDbContext())
{
    var query = from left in context.LeftTables
                join right in context.RightTables on left.Id equals right.Id into joinedTables
                from right in joinedTables.Where(r => r.Description.Contains("keyword")).DefaultIfEmpty()
                select new { left, right };

    foreach (var result in query)
    {
        Console.WriteLine($"LeftTable: {result.left.Name}, RightTable: {result.right?.Description}");
    }
}