AyeSQL
Aye /ʌɪ/ exclamation (archaic dialect): said to express assent; yes.
AyeSQL is a small Elixir library for using raw SQL.
Why raw SQL?
Writing and running raw SQL in Elixir is not pretty. Not only the lack of syntax highlighting is horrible, but also substituting parameters into the query string can be unmaintainable e.g:
query =
"""
SELECT hostname, AVG(ram_usage) AS avg_ram
FROM server
WHERE hostname IN ($1, $2, $3)
AND location = $4
GROUP BY hostname
"""
arguments = ["server_0", "server_1", "server_2", "Barcelona"]
Postgrex.query(conn, query, arguments)
Adding more hostname
s to the previous query is a nightmare, editing strings
to add the correct index to the query.
Thankfully, we have Ecto, which provides a great DSL for generating database queries at runtime. The same query in Ecto e.g:
servers = ["server_0", "server_1", "server_2"]
location = "Barcelona"
from s in "server",
where: s.location == ^location and s.hostname in ^servers,
select: %{hostname: s.hostname, avg_ram: avg(s.ram_usage)}
Pretty straightforward and maintainable.
So, why raw SQL?. Though Ecto is quite good with simple queries, complex queries often require the use of fragments, ruining the abstraction and making the code harder to read e.g:
Let's say we have the following
SQL query
to retrieve the click count of a certain type of link every day of the last X
days. In raw SQL this could be written as:
WITH computed_dates AS (
SELECT dates::date AS date
FROM generate_series(
current_date - $1::interval,
current_date - interval '1 day',
interval '1 day'
) AS dates
)
SELECT dates.date AS day, count(clicks.id) AS count
FROM computed_dates AS dates
LEFT JOIN clicks AS clicks ON date(clicks.inserted_at) = dates.date
WHERE clicks.link_id = $2
GROUP BY dates.date
ORDER BY dates.date;
Where $1
is the interval (%Postgrex.Interval{}
struct) and $2
is some
link ID. The query is easy to understand and easy to maintain.
The same query in Ecto could be written as:
dates =
"""
SELECT generate_series(
current_date - ?::interval,
current_date - interval '1 day',
interval '1 day'
)::date AS d
"""
from(
c in "clicks",
right_join: day in fragment(dates, ^days),
on: day.d == fragment("date(?)", c.inserted_at),
where: c.link_id = ^link_id
group_by: day.d,
order_by: day.d,
select: %{
day: fragment("date(?)", day.d),
count: count(c.id)
}
)
The previous code is hard to read and hard to maintain:
- Not only knowledge of SQL is required, but also knowledge of the intricacies of using Ecto fragments.
- Queries using fragments cannot use aliases defined in schemas, so the code becomes inconsistent.
Overview
Inspired on Clojure library Yesql, AyeSQL tries to find a middle ground between those two approaches by:
- Keeping the SQL in SQL files.
- Generating Elixir functions for every query.
- Having named parameters and query composability easily.
Using the previous query, we would create a SQL file with the following contents:
-- name: get_day_interval
-- docs: Gets days interval.
SELECT datetime::date AS date
FROM generate_series(
current_date - :days::interval, -- Named parameter :days
current_date - interval '1 day',
interval '1 day'
);
-- name: get_avg_clicks
-- docs: Gets average click count.
WITH computed_dates AS ( :get_day_interval )
SELECT dates.date AS day, count(clicks.id) AS count
FROM computed_date AS dates
LEFT JOIN clicks AS clicks ON date(clicks.inserted_at) = dates.date
WHERE clicks.link_id = :link_id -- Named parameter :link_id
GROUP BY dates.date
ORDER BY dates.date;
In Elixir we would load all the queries in this file by creating the following module:
defmodule Queries do
use AyeSQL, repo: MyRepo
defqueries("queries.sql") # File name with relative path to SQL file.
end
or using the macro defqueries/3
:
import AyeSQL, only: [defqueries: 3]
defqueries(Queries, "queries.sql", repo: MyRepo)
Both approaches will create a module called Queries
with all the queries
defined in "queries.sql"
.
And then we could execute the query as follows:
iex(1)> params = %{
iex(1)> link_id: 42,
iex(1)> days: %Postgrex.Interval{secs: 864_000} # 10 days
iex(1)> }
iex(2)> Queries.get_avg_clicks(params, run?: true)
{:ok, [
%{day: ..., count: ...},
...
]}
Syntax
A SQL file can have as many queries as you want as long as they are named.
Before the query, add a comment with the keyword name:
. This name will be
used for the functions' names e.g
-- name: get_servers
-- docs: Generates the functions get_servers/1 and get_servers/2
SELECT hostname FROM server;
And optionally they can have:
- Named parameters: Identified by a
:
followed by the name of the parameter e.g:
-- These functions receive a map or a Keyword with the parameter :hostname.
-- name: get_server
SELECT * FROM server WHERE hostname = :hostname;
- SQL queries calls: Identified by a
:
followed by the name of the query in the same file e.g:
-- name: get_locations
SELECT id
FROM location
WHERE region = :region;
-- This will compose :get_locations with get_servers_by_location.
-- The function will receive a map or a Keyword with the parameter :region.
-- name: get_servers_by_location
SELECT *
FROM servers
WHERE location_id IN ( :get_locations );
- Named optional parameters: Identified by a
:_
followed by the name of the parameter e.g:
-- name: get_servers
SELECT *
FROM server
WHERE hostname = :hostname
:_by_location
-- name: by_location
AND location = :location
then we could compose the queries as follow:
For:
SELECT * FROM server WHERE hostname = :hostname
it would be called like this:
Queries.get_servers(hostname: "server0")
For:
SELECT * FROM server WHERE hostname = :hostname AND location = :location
it would be called like this:
Queries.get_servers( hostname: "server0", location: "Barcelona", :_by_location: &Queries.by_location/2 )
- Documentation: Before the query, add a comment with the keyword
docs:
. This string will be used as documentation for the function e.g:
-- name: get_servers
-- docs: Gets all the servers hostnames.
SELECT hostname
FROM server;
IN
statement
Let's say we have the following query loaded in the module Server
:
-- name: get_avg_ram
SELECT hostname, AVG(ram_usage) AS avg_ram
FROM server
WHERE hostname IN (:hostnames)
AND location = :location
GROUP BY hostname;
It is possible to do the following:
iex(1)> hosts = ["server_0", "server_1", "server_2"]
iex(2)> params = %{hostnames: {:in, hosts}, location: "Barcelona"}
iex(3)> Server.get_avg_ram(params, run?: true)
{:ok, [
%{hostname: "server_0", avg_ram: ...},
%{hostname: "server_1", avg_ram: ...},
%{hostname: "server_2", avg_ram: ...},
]}
Query composability at runtime
Let's say we have the following query loaded in the module Server
:
-- name: get_servers
SELECT hostname
FROM server
WHERE region = :region;
It is possible to do the following:
iex(1)> query = &Server.get_servers/2
iex(2)> params = %{hostnames: query, location: "Barcelona", region: "Spain"}
iex(3)> Server.get_avg_ram(params, run?: true)
{:ok, [
%{hostname: ...},
...
]}
Query runners
The purpose of runners is to be able to implement other database adapters.
By default, AyeSQL
uses the runner AyeSQL.Runner.Ecto
. This runner only has
one option which is :repo
for the repo module. Additionally, it converts the
result to a list of maps.
Using other runners is as easy as setting them in the module definition as follows:
defmodule MyQueries do
use AyeSQL, runner: IdemRunner, repository: MyRepo
...
end
For runners, there is only one callback to be implemented.
run/3
: which receives aAyeSQL.statement()
,AyeSQL.arguments()
and akeyword()
list with extra options for the runner (mandatory).
The following would be a runner for Ecto
that does nothing to the result
(returns Postgrex.Result.t()
and Postgrex.Error.t()
structs):
defmodule IdemRunner do
use AyeSQL.Runner
@impl true
def run(stmt, args, options) do
repo = options[:repository] || raise ArgumentError, "No repo defined"
Ecto.Adapters.SQL.query(repo, stmt, args)
end
end
Installation
AyeSQL
is available as a Hex package. To install, add it to your
dependencies in your mix.exs
file:
def deps do
[{:ayesql, "~> 0.4"}]
end
If you're going to use any of the provided query runners, then you should add their dependencies as well:
- Add
:ecto_sql
forAyeSQL.Runner.Ecto
(default runner). - Add
:postgrex
forAyeSQL.Runner.Postgrex
. - Add
:ecto_sql
and:postgrex
for running queries usingEcto
in aPostgreSQL
database.
Author
Alexander de Sousa.
License
AyeSQL
is released under the MIT License. See the LICENSE file for further
details.