# Dymo
[](https://ci.emage.run/the-missing-link/dymo)
[](https://codecov.io/gh/the-missing-link/dymo)
[](https://hex.pm/packages/dymo)
For all your labelling and tagging needs!
## Motivations
When it comes to polymorphism, it's always hard to find a match-all solution. Each known implementation have tradeoffs:
1. Real polymorphism (`taggable_id`, `taggable_type` on the `Taggings` model) breaks database level foreign keys, and makes requests slower.
2. Parent entity (Having each model have a `entity_id` refering to some `Entity` model) and having tags assigned to the `Entity` model via `entity_id` is cumbersome when performing complex queries and reverse queries.
3. Multiple nullable foreign keys on the `Taggings` model (Eg `user_id`, `post_id`) is a very good solution but it could become hard to maintain and enforce if many models are taggable.
4. One join table per taggable model (Eg `users_tags` and `posts_tags`) make it impossible to consolidate and search using SQL queries only.
This package offers an implementation that fits the 3rd and 4th approaches, and it offers shortcuts and mix tasks to make your life easier.
## Installation
If [available in Hex](https://hex.pm/docs/publish), the package can be installed
by adding `dymo` to your list of dependencies in `mix.exs`:
```elixir
def deps do
[
{:dymo, "~> 0.1.0"}
]
end
```
Then, you can install the `Tag` migration in your application (Note that for umbrella apps, you'll need to first `cd` into the app containing your repo migrations):
```bash
$ mix dymo.install
* creating priv/repo/migrations
* creating priv/repo/migrations/20180828154957_create_tag.exs
```
Once done, you should start and make a join table for the model(s) you want to be able to label. There is a mix task for this too!
```bash
$ mix dymo.join_table MyApp.Post
* creating priv/repo/migrations
* creating priv/repo/migrations/20180828154958_create_posts_tags.exs
Once your database gets migrated, a new table posts_tags will be created.
You might want to add the following relationship to your MyApp.Post schema:
many_to_many :tags, Dymo.Tag,
join_through: "posts_tags",
on_replace: :delete,
unique: true
```
If you follow the directives given by the tasks, you should then have a fully labellable Post model. Congratulations!
Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)
and published on [HexDocs](https://hexdocs.pm). Once published, the docs can
be found at [https://hexdocs.pm/dymo](https://hexdocs.pm/dymo).
