参考文档:Dapper one to many

Table

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int Born { get; set; }
    public Country Residience { get; set; }
    public ICollection<Book> Books { get; set; }
}

public class Country
{
    public int CountryId { get; set; }
    public string CountryName { get; set; }
}

public class Book
{
    public int BookId { get; set; }
    public string BookName { get; set; }
}

C# Code

pulic List<Person> GetPersons(){
 var sql = @"SELECT 1 AS Id, 'Daniel Dennett' AS Name, 1942 AS Born, 1 AS CountryId, 'United States of America' AS CountryName, 1 AS BookId, 'Brainstorms' AS BookName
UNION ALL SELECT 1 AS Id, 'Daniel Dennett' AS Name, 1942 AS Born, 1 AS CountryId, 'United States of America' AS CountryName, 2 AS BookId, 'Elbow Room' AS BookName
UNION ALL SELECT 2 AS Id, 'Sam Harris' AS Name, 1967 AS Born, 1 AS CountryId,  'United States of America' AS CountryName, 3 AS BookId, 'The Moral Landscape' AS BookName
UNION ALL SELECT 2 AS Id, 'Sam Harris' AS Name, 1967 AS Born, 1 AS CountryId,  'United States of America' AS CountryName, 4 AS BookId, 'Waking Up: A Guide to Spirituality Without Religion' AS BookName
UNION ALL SELECT 3 AS Id, 'Richard Dawkins' AS Name, 1941 AS Born, 2 AS CountryId,  'United Kingdom' AS CountryName, 5 AS BookId, 'The Magic of Reality: How We Know What`s Really True' AS BookName
UNION ALL SELECT 3 AS Id, 'Richard Dawkins' AS Name, 1941 AS Born, 2 AS CountryId,  'United Kingdom' AS CountryName, 6 AS BookId, 'An Appetite for Wonder: The Making of a Scientist' AS BookName";

var remainingHorsemen = new Dictionary<int, Person>();
connection.Query<Person, Country, Book, Person>(sql, (person, country, book) => {
    //person
    Person personEntity;
    //trip
    if (!remainingHorsemen.TryGetValue(person.Id, out personEntity))
    {
        remainingHorsemen.Add(person.Id, personEntity = person);
    }

    //country
    if(personEntity.Residience == null)
    {
        if (country == null)
        {
            country = new Country { CountryName = "" };
        }
        personEntity.Residience = country;
    }                    

    //books
    if(personEntity.Books == null)
    {
        personEntity.Books = new List<Book>();
    }

    if (book != null)
    {
        if (!personEntity.Books.Any(x => x.BookId == book.BookId))
        {
            personEntity.Books.Add(book);
        }
    }

    return personEntity;
}, 
splitOn: "CountryId,BookId");

return remainingHorsemen.Value.ToList();