add support for 1 to many relationships

[drujensen]

Create two new macros: belongs_to and has_many

require "./post"

class Comment < Kemalyst::Model
  belongs_to post
  ...
end

This will create a mapping to the post_id : Int64 field and generate a method that will query the parent and return it.

def post
  Post.find post_id
end

require "./comment"

class Post < Kemalyst::Model
  has_many comments
  ...
end

This will create a method called comments that will query the children records.

def comments
  Comments.all("JOIN posts ON posts.id = comments.post_id WHERE posts.id = ?", id)
end

Options to override the field names and types should be considered for legacy database mappings.

One of the difficulties is requiring the other model. Macros do not allow you to inject require into the class.

Another issue is the N+1 queries for comments. I think we can find ways of optimizing this later.

[elorest]

I would suggest that all of the models should be loaded into the main project file.

#src/blog.cr
require "./models/*"

[drujensen]

can you require all subdirectories as well? does this work in crystal? require "./models/**/*"

[drujensen]

found it: https://crystal-lang.org/docs/syntax_and_semantics/requiring_files.html

require "./models/**"

[elorest]

Both of those will work.

[andrewzah]

I'll try and take a stab at this in the next few weeks.

[migeorge]

Closing since #52 was merged.