wp-how-to-use-petapoco-with-umbraco-09.cs

var sql = new Sql()
    .Select("Movies.*, Directors.*")
    .From<Movie>(dbContext.SqlSyntax)
    .InnerJoin<Director>(dbContext.SqlSyntax)
    .On<Movie, Director>(dbContext.SqlSyntax, m => m.DirectorId, d => d.Id);

var movies = dbContext.Database.Fetch<Movie, Director, Movie>((m, d) =>
{
    m.Director = d;

    return m;
}, sql);