Trying to understand Dapper Multi Mapping

Question

I have been going through Dapper's Multi Mapping documentation but remain confused.

This is the example from Dapper documentation

class Post { public int Id { get; set; } public string Title { get; set; } public string Content { get; set; } public User Owner { get; set; } } class User { public int Id { get; set; } public string Name { get; set; } } var sql = @"select * from #Posts p left join #Users u on u.Id = p.OwnerId Order by p.Id"; var data = connection.Query<Post, User, Post>(sql, (post, user) => { post.Owner = user; return post;}); var post = data.First();

What confuses me is where the variable post and user came from? I see in this line ...

connection.Query<Post, User, Post>

that Post and User are the models and I understand that ..

(post, user) => { post.Owner = user; return post;}

is a function that defines the mapping, but where do post and user get instantiated?

They don't "come from" anywhere, it's a lambda expression, go have a read about them :) — DavidG
– DavidG, Commented Apr 12, 2017 at 13:33

SomeoneLost · Accepted Answer · 2017-04-12 13:39:35Z

Its a Lambda function. Don't know the technical explanation, but basically connection.Query returns multiple records, each containing a post and user as per the query. With (post, user) => you're declaring that post will represent the Post and user will represent the User from each record.

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