Fun with ChicagoBoss Models

I decided to create some examples for CB Model API documentation.

Let’s say we want to create a basic 1:Many entity relationship between a blog post and comments in our hypothetical blog software. 1 blog post can have 0 or many comments. Create a new empty ChicagoBoss application by running:

git clone git://
cd ChicagoBoss
make app PROJECT=blogy
cd ../blogy

Create a model for a blog post. Put this into src/model/post.erl

-module(post, [Id, PostTitle, PostText]).
-has({comments, many}).

Each blog post can have many comments, CB requires that you add -has({comments, many}). to the module declaration. Note that the comment model name must end with s as the first element in the tuple (tag of the tuple).

Comment must belong to a post. We add a simple length of the PostId check into validation_tests/0. Put this into src/model/comment.erl

-module(comment, [Id, PostId, CommentAuthor, CommentText]).

validation_tests() -> [{fun() -> length(PostId) > 0 end, "Comment must have a post."}].
(wildbill@f15)1> P1 = post:new(id, "Awesome first post", "ftw").
{post,id,"Awesome first post","ftw"}
(wildbill@f15)2> {ok, P1Saved} = P1:save().
{ok,{post,"post-1","Awesome first post","ftw"}}
(wildbill@f15)3> P1Saved:id().
(wildbill@f15)4> C1 = comment:new(id, P1Saved:id(), "Anonymous", "Comment text").
{comment,id,"post-1","Anonymous","Comment text"}

At this point, the shell has variable C1 representing a new comment that is associated with our first blog post.

(wildbill@f15)5> C1:belongs_to().
[{post,{post,"post-1","Awesome first post","ftw"}}]
(wildbill@f15)6> {ok, C1Saved} = C1:save().
{ok,{comment,"comment-2","post-1","Anonymous", "Comment text"}}
(wildbill@f15)7> C1Saved:belongs_to_names().

5 thoughts on “Fun with ChicagoBoss Models”

  1. You said : Note that the comment model name must end with s as the first element in the tuple (tag of the tuple).
    I do not think so
    (cbmock@localhost)49> B=breed:new(id,”Bread”)
    (cbmock@localhost)49> .
    (cbmock@localhost)50> {ok,Bs}=B:save()
    (cbmock@localhost)50> .
    (cbmock@localhost)51> P=puppy:new(id,”Puppy”,Bs:id())
    (cbmock@localhost)51> .
    (cbmock@localhost)52> {ok,P2}=P:save().
    (cbmock@localhost)53> boss_bd:find(puppy,[])
    (cbmock@localhost)53> .
    ** exception error: undefined function boss_bd:find/2
    (cbmock@localhost)54> boss_db:find(puppy,[])
    (cbmock@localhost)54> .
    (cbmock@localhost)55> boss_db:find(breed,[])
    (cbmock@localhost)55> .
    (cbmock@localhost)56> Sb=boss_db:find(“breed-5″)
    (cbmock@localhost)56> .
    (cbmock@localhost)57> SP=boss_db:find(“puppy-5”)
    (cbmock@localhost)57> .
    (cbmock@localhost)58> Sp=boss_db:find(“puppy-6″)
    (cbmock@localhost)58> .
    (cbmock@localhost)59> Sp:belongs_to().
    (cbmock@localhost)60> Sb:puppy().

  2. Big thanks for your articles, they are very useful for beginners like me!
    I’m beginning to learn erlang and chicago boss and I’d like to use it in little project with mongodb as a database which is also new to me. But can’t find any good tutorial from people who had experience with chicago boss models and mongodb, how to use them together.
    If you know link to such tutorial or have own experience, it would be very helpful if you share your knowledge.

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