Intermediate SQL with Ecto - LoneStar ElixirConf 2018

Intermediate
SQL with Ecto
Dennis Beatty

@dnsbty

GET https://mybusiness.googleapis.com/v4/
{parent=accounts/*/locations/*}/reviews

defmodule GMB.Reviews.Review do
use Ecto.Schema
schema "reviews" do
field :id, :string
field :author, :string
field :rating, :integer
field :reply, :string
field :created_at, :utc_datetime
field :updated_at, :utc_datetime
field :deleted_at, :utc_datetime
end
end
(ArgumentError) field/association :id
is already set on schema

defmodule GMB.Reviews.Review do
use Ecto.Schema
@primary_key {:id, :string, []}
schema "reviews" do
field :author, :string
field :comment, :string
field :rating, :integer
field :reply, :string
field :created_at, :utc_datetime
field :updated_at, :utc_datetime
field :deleted_at, :utc_datetime
end
end

defmodule GMB.Repo.Migrations.CreateReviews do
use Ecto.Migration
def change do
create table(:reviews) do
add :author, :string, null: false, default: ""
add :rating, :integer, null: false, default: 0
add :comment, :string, null: false, default: ""
add :reply, :string, null: false, default: ""
add :created_at, :naive_datetime, null: false, default: "epoch"
add :updated_at, :naive_datetime, null: false, default: "epoch"
add :deleted_at, :naive_datetime, null: false, default: "epoch"
end
end
end

defmodule GMB.Repo.Migrations.CreateReviews do
use Ecto.Migration
def change do
create table(:reviews, primary_key: false) do
add :id, :string, primary_key: true
add :author, :string, null: false, default: ""
add :rating, :integer, null: false, default: 0
add :comment, :string, null: false, default: ""
add :reply, :string, null: false, default: ""
add :created_at, :naive_datetime, null: false, default: "epoch"
add :updated_at, :naive_datetime, null: false, default: "epoch"
add :deleted_at, :naive_datetime, null: false, default: "epoch"
end
end
end

User
id - Integer
ﬁrst_name - String
last_name - String
email - String
Group
id - Integer
name - String
description - String
slug - String
Member
user_id - Integer
group_id - Integer
role - String

defmodule SirAlex.Groups.Member do
use Ecto.Schema
alias SirAlex.Groups.{Group, User}
@primary_key false
schema "members" do
field :role, :string, default: "member"
belongs_to :group, Group
belongs_to :user, User
timestamps()
end
end

defmodule SirAlex.Repo.Migrations.CreateMembers do
use Ecto.Migration
def change do
create table(:members, primary_key: false) do
add :group_id, references(:groups), primary_key: true
add :user_id, references(:users), primary_key: true
add :role, :string, null: false, default: "member"
timestamps()
end
end
end

defmodule SirAlex.Accounts.User do
schema "users" do
...
many_to_many :groups, Group, join_through: Member
...
end
end

defmodule GMB.Reviews do
alias GMB.Repo
alias GMB.Reviews.Review
def save_reviews(reviews) do
Enum.map(reviews, &save_review/1)
end
def save_review(attrs) do
%Review{}
|> Review.changeset(attrs)
|> Repo.insert()
end
end

INSERT INTO “reviews"
(“author”,"comment",
“created_at",“id",
"rating","reply")
VALUES
('Dennis','Elixir is awesome’,
‘2018-02-24T07:15:19.730704Z','s929u9dswrf9348',
5,'Yeah, it is!');

• Check out a DB connection from the pool

• Send review data to the DB

• Wait for response from DB

• Release the DB connection back to the pool

INSERT INTO “reviews"
(“author”,"comment",
“created_at",“id",
"rating","reply")
VALUES
('Dennis','Elixir is awesome’,
‘2018-02-24T07:15:19.730704Z','s929u9dswrf9348',
5,'Yeah, it is!’),
(‘Brett','Best BBQ place around.’,
‘2018-02-21T03:26:01.359302Z','sldfi304jslfi3l',
5,’Thanks!’);

defmodule GMB.Reviews do
alias GMB.Repo
alias GMB.Reviews.Review
Repo.insert_all(Review, reviews)
end
end
No validation?! 😱

** (Postgrex.Error) ERROR 23505
(unique_violation): duplicate key
value violates unique constraint
"reviews_pkey"

opts = [on_conflict: :nothing]
Repo.insert_all(Review, reviews, opts)
end

opts = [on_conflict: :replace_all]
end
** (Postgrex.Error) ERROR 42601
(syntax_error): ON CONFLICT DO UPDATE
requires inference specification or
constraint name

opts = [
on_conflict: :replace_all,
conflict_target: :id
]
end

opts = [
on_conflict: [set: [comment: "updated"]],
]
end

query = from r in Review, update: [set: [comment:
fragment("EXCLUDED.comment")]]
opts = [
on_conflict: query,
]
end

https://goo.gl/DMof8Q

Under the Hood
• Get next val from sequence*

• Insert row with value from sequence

• If unique constraint error, run ON CONFLICT clause

reviews = [
%{
author: "Dennis",
comment: "Elixir is awesome",
created_at: #DateTime<2018-02-24 09:10:21.752944Z>,
id: "s929u9dswrf9348",
rating: 5,
reply: "Yeah, it is!"
},
%{
author: "Brett",
comment: "I wish I'd found Elixir sooner",
id: "wod938wlfu",
rating: 5,
reply: "Too bad"
}
]

iex> Reviews.save_reviews(reviews)
{2, nil}

query = from r in Review, update: [set:
[comment: fragment("EXCLUDED.comment")]]
opts = [
on_conflict: query,
conflict_target: :id,
returning: true
]
end

iex> Reviews.save_reviews(reviews)
{2,
[
%GMB.Reviews.Review{
__meta__: #Ecto.Schema.Metadata<:loaded, "reviews">,
author: "Dennis",
comment: "Elixir is awesome",
deleted_at: #DateTime<1970-01-01 00:00:00.000000Z>,
id: "s929u9dswrf9348",
rating: 5,
reply: "Yeah, it is!",
updated_at: #DateTime<1970-01-01 00:00:00.000000Z>
},
%GMB.Reviews.Review{
__meta__: #Ecto.Schema.Metadata<:loaded, "reviews">,
author: "Brett",
comment: "I wish I'd found Elixir sooner",
deleted_at: #DateTime<1970-01-01 00:00:00.000000Z>,
id: "wod938wlfu",
rating: 5,
reply: "Too bad",
updated_at: #DateTime<1970-01-01 00:00:00.000000Z>
}
]}

Further Reading
• Plataformatec - What’s New in Ecto 2.1 
http://pages.plataformatec.com.br/ebook-whats-new-in-ecto-2-0

• Ecto Docs!  
https://hexdocs.pm/ecto/Ecto.html

• @dnsbty on twitter

Intermediate SQL with Ecto - LoneStar ElixirConf 2018

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