Abandoning models - embracing data

@michalmuskala Warszawa, 9.06.2016
Abandoning models - embracing data
A gentle introduction to Ecto

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Michał Muskała
http://michal.muskala.eu/
https://github.com/michalmuskala/
@michalmuskala

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The Experiment

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Who used Elixir?

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Who used Ecto?

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Who has Ruby background?

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Who has C# or .NET background?

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Inspirations
LINQ - queries
ActiveRecord - associations
Other Elixir projects - Moebius - pipeline queries
Other Ruby projects - rom, trailblazer - focus on data

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Adapter-based architecture
Database adapters
Connection pool adapters
db_connection library

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Ecto
Ecto.Schema
Ecto.Query
Ecto.Repo
Ecto.Changeset

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Ecto.Schema
defmodule Weather do
use Ecto.Schema
schema "weather" do
belongs_to :city, City
field :wdate, Ecto.Date
field :temp_lo, :integer
field :temp_hi, :integer
field :prcp, :float, default: 0.0
timestamps
end
end

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Ecto.Schema
declares ﬁelds - no SELECT * FROM foos
allows for custom types
thin wrapper around Elixir’s structs
deﬁnes data - not behaviour

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Ecto.Query
from w in Weather,
where: w.prcp <= 0.0 or is_nil(w.prcp),
select: w
from s in Search,
where: ilike(fragment("?::text", s.name),
^name_search_term) or
fragment("to_tsvector(?) @@ to_tsquery(?)",
s.description, ^term)

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Ecto.Query
from p in Post,
where: fragment(position: ["$geoWithin": [...]])
def all(filter) do
filter.q
|> sanitize
|> search
|> preload(:location)
|> order_by([s] asc: s.date, desc: s.type)
end

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Ecto.Query
defmacrop geo_search(coordinates, geo_point, radius) do
quote do
fragment("ST_DWithin(?, ?, ?)",
unquote(coordinates),
unquote(geo_point),
unquote(radius)
)
end
end

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Ecto.Query
def by_location(query, %{lat: lat, lng: lng, radius: radius}) do
geo_point = %Geo.Point{coordinates: {lat, lng}}
from provider in query,
left_join: location_provider in assoc(provider, :location),
left_join: events in assoc(provider, :events),
left_join: location_event in assoc(events, :location),
where:
geo_search(location_provider.coordinates, ^geo_point, ^radius)
or
geo_search(location_event.coordinates, ^geo_point, ^radius),
distinct: true,
select: provider
end

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Ecto.Query
query = from p in Post,
select: [:visits],
order_by: [desc: :visits],
limit: 10
TestRepo.all(from p in subquery(query),
select: avg(p.visits))

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Ecto.Query
Two syntaxes - keyword and pipeline
No lazy-loading, explicit preloads
Easily extensible via fragments and macros
Translated by adapter
Composable

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Ecto.Repo
defmodule Simple.Repo do
use Ecto.Repo, otp_app: :simple
end
def start(_type, _args) do
import Supervisor.Spec
tree = [supervisor(Simple.Repo, [])]
opts = [name: Simple.Sup, strategy: :one_for_one]
Supervisor.start_link(tree, opts)
end

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Ecto.Repo
Isolates all impure operations
Is an interface to the database
Outside of repo - everything is plain data

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Ecto.Changeset
Encodes data changes as a data structure
No validations are global
Multiple changieret functions for different circumstances
Easily extensible with functions

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Ecto.Multi
def password_reset_multi(account, params) do
account = account_password_reset(account, params)
access_log = log_password_reset(account, params)
Multi.new
|> Multi.update(:account, account)
|> Multi.insert(:log, access_log)
|> Multi.delete_all(:sessions, assoc(account, :sessions))
end

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Ecto.Multi
defmodule UserManager do
def password_reset(params) do
with {:ok, account} <- load_account(params),
multi = password_reset_multi(account, params),
{:ok, results} <- Repo.transaction(multi),
:ok <- send_notification(results.account),
do: {:ok, results.account}
end
# ...
end

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Ecto.Multi
Encodes transaction as a data structure
Changesets for transactions
You can test your transaction without database!

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Schema less queries
from u in "users",
join: a in "activities",
on: a.user_id == u.id,
where: a.start_at > type(^start_at, Ecto.DateTime) and
a.end_at < type(^end_at, Ecto.DateTime),
group_by: a.user_id,
select: %{user_id: a.user_id,
interval: a.start_at - a.end_at,
count: count(u.id)}

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Schema less queries
# insert data
[%{id: id}] =
MyApp.Repo.insert_all("posts", [[title: "hello"]],
returning: [:id])
# use query for updates
post = from p in "posts", where: p.id == ^id
{1, _} = MyApp.Repo.update_all(post,
set: [title: "new title"])
# and deletes
{1, _} = MyApp.Repo.delete_all post

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Table less schemas
defmoudule RegistrationSchema do
use Ecto.Schema
schema "" do
field :foo, :string
field :bar, :integer
embeds_one :resource, Resource
end
# ...
end

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Schema less changesets
data = %{}
types = %{first_name: :string,
last_name: :string,
email: :string}
fields = Map.keys(types)
changeset =
{data, types}
|> Ecto.Changeset.cast(params, fields)
|> validate_required(...)
|> validate_length(...)

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Concurrent, transactional tests
In 1.1 - database tests sequential, 2.0 - concurrent
Works with postgres, mysql has wired transaction semantics
Works with Wallaby and Hound

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No models, no callbacks
Ecto 1.1 deprecated models, embraced schemas, 2.0 removes models
Ecto 1.1 deprecated callbacks, 2.0 removed them
I’m forbidden by José to use the world “model”
Phoenix will switch away from the model nomenclature

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KISS
Plain CRUD interfaces are easy
When you need more power - you have it
We want not to force anything on the users, but keep the simplicity

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–José Valim
“I am completely OK with taking the blame regarding Ecto 1.0. We did
push folks to the wrong direction. But Ecto 2.0 no longer puts you in
this place[…]. If you are using structs as your domain models, then it
will be more on you than on me, since you have everything to stop
doing that[…].”

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Abandoning models - embracing data

Abandoning models - embracing data

Michał Muskała

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