Given this test:
public class Author { public int AuthorId { get; set; } public List<Book> Books { get; set; } = new List<Book>(); } public class Book { public int BookId { get; set; } } [Fact] public async Task DapperCollapseLeftJoin() { var sql = @" select 1 as AuthorId, 1 as BookId union select 1 as AuthorId, 2 as BookId union select 2 as AuthorId, 3 as BookId union select 2 as AuthorId, 4 as BookId"; var authorsWithBooks = (await AC.OpenConnection.QueryAsync<Author, Book, Author>(sql, (author, book) => { author.Books.Add(book); return author; }, splitOn: "AuthorId, BookId")).ToList(); // fails because we're getting 4 author+book rows Assert.Equal(2, authorsWithBooks.Count); } The documentation for Dapper says multimapping maps rows to multiple objects and doesn't mention anything about actually collapsing objects (like would happen for left/inner joins where leftmost column values repeat).
Is there a Dapper-native way to make this happen?
