# Dymo
[](https://ci.linky.one/tableturn/dymo)
[](https://codecov.io/gh/tableturn/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_tags.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 can add the tags relationship with dedicated macro in your MyApp.Post schema:
```elixir
schema "..." do
tags()
end
```
If you follow the directives given by the tasks, you should then have
a fully labellable Post model. Congratulations!
## Using Dymo.Taggable
When a module uses `Dymo.Taggable`, many shortcut functions are
meta-programmed into it.
It becomes easy to achieve labelling-related tasks. All the examples
bellow assyme that a `Post` module calls `use Dymo.Taggable`.
### Editing Labels
To set the tags on an instance of a post:
```elixir
Post.set_labels(post, ~w(ten eleven))
```
Similarily, you can add / remove labels using `Post.add_labels/2` and `Post.remove_labels/2`.
### Querying Labels
To get the labels associated with a given post, you have several options.
Using the association directly if you defined it:
```elixir
post
|> Repo.preload(:tags)
|> Map.get(:tags)
|> Enum.map(&(&1.label))
#
```
Using the helper function:
```elixir
post
|> Post.labels()
```
Note that the `Post.labels/1` also accepts a module directly as an input - in that case it would return all labels that were ever associated with posts.
You can also query models that are tagged with specific labels by doing the following:
```elixir
Post.labelled_with(~w(ten eleven))
```
## Notes
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).
## Changes
### 0.3.4
- Adds some more spec.
### 0.3.3
- Adds some more spec.
### 0.3.2
- Use protocols for dispatching labelling functions to implementation
- Add generic `Taggable` functions for using the `Taggable.Protocol`
protocol
### 0.3.1
- Add support for `:binary_id` primary key for taggable structures
### 0.3.0
- `Dymo.Tagger.query_labels/2` become
`Dymo.Tagger.query_all_labels/{2,3}`. See below for semantic of
third argument.
- `Dymo.Tagger.query_labels/3` become
`Dymo.Tagger.query_labels/{3,4}`. See below for semantic of third
argument.
- This version adds support for namespaces. Namespaces allows to
isolate labels. `Dymo.Taggable` generated functions can take as
additional argument a namespace on which to apply the function.
WARNING: no namespace means ~root~ namespace, not all namespaces.
- `set_labels/3`: set all tags for a given namespace, keeping others untouched
- `add_labels/3`: add labels to the given namespace
- `remove_labels/3`: remove labels from the given namespace
- `all_labels/1`: returns all labels of the given namespace for a module
- `labels/2`: return all labels for the given struct and namespace
### 0.2.0
- Add compatiblity with Ecto 3.x
### 0.1.x
- Compatible with Ecto 2.x
