qckdev.Data.Linq

using System;	
using System.Collections.Generic;

namespace Entities
{
	sealed class TestHeader
	{
		public Guid TestHeaderId { get; set; }
		public string Name { get; set; }
		
		public IEnumerable<TestLine> Lines { get; set; }
	}

	sealed class TestLine
	{
		public Guid TestLineId { get; set; }
		public Guid TestHeaderId { get; set; }
		public string Description { get; set; }

		public TestHeader Header { get; set; }

	}
}

using System;
using System.Linq;
using qckdev.Data.Linq;


context.TestHeaders
	.Include(x => x.Lines)
	.WhereString("First line",
		x => x.Name,
		x => x.Lines.Select(x => x.Description)
	);