AyeSQL
Aye /ʌɪ/ exclamation (archaic dialect): said to express assent; yes.
AyeSQL is a 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 hostnames to the previous query would be a nightmare. If
the arguments
are generated dynamically, then editing this query would be
a challenging task.
Thankfully, we have Ecto, which provides a great DSL for generating database queries at runtime. The same query in Ecto would be the following:
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.
If Ecto is so good for building queries, why would you use 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 an
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 mandatory and optional named parameters.
- Allowing query composability with ease.
Using the previous query, we would create a SQL file with the following contents:
-- name: get_day_interval
-- This query do not have docs, so it's private.
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 ) -- Composing with another query
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> params = [
...> link_id: 42,
...> days: %Postgrex.Interval{secs: 864_000} # 10 days
...> ]
iex> Queries.get_avg_clicks(params, run?: true)
{:ok,
[
%{day: ..., count: ...},
...
]
}
Syntax
An SQL file can have as many queries as you want as long as they are named.
For the following sections we'll assume we have:
lib/my_repo.ex
which is anEcto
repo calledMyRepo
.lib/queries.sql
with SQL queries.lib/queries.ex
with the following structure:import AyeSQL, only: [defqueries: 3] defqueries(Queries, "queries.sql", repo: MyRepo)
Running the queries by default by adding the following in
config/config.exs
:config ayesql, run?: true
Naming Queries
For naming queries, we add a comment with the keyword -- name:
followed by
the name of the function e.g the following query would generate the function
Queries.get_hostnames/2
:
-- name: get_hostnames
SELECT hostname FROM server
Additionally, we could also add documentation for the query by adding a comment
with the keyword -- docs:
followed by the query's documentation e.g:
-- name: get_hostnames
-- docs: Gets hostnames from the servers.
SELECT hostname FROM server
Important: if the function does not have
-- docs:
it won't have documentation e.g.@doc false
.
Named Parameters
There are two types of named parameters:
- Mandatory: for passing parameters to a query. They start with
:
e.g.:hostname
. - Optional: for query composability. The start with
:_
e.g.:_order_by
.
Additionaly, any query in a file can be accessed with its name adding :
at
the front e.g :get_hostnames
.
Mandatory Parameters
Let's say we want to get the name of an operative system by architecture:
-- name: get_os_by_architecture
-- docs: Gets operative system's name by a given architecture.
SELECT name
FROM operative_system
WHERE architecture = :architecture
The previous query would generate the function
Queries.get_os_by_architecture/2
that can be called as:
iex> Queries.get_os_by_architecture(architecture: "AMD64")
{:ok,
[
%{name: "Debian Buster"},
%{name: "Windows 10"},
...
]
}
Query Composition
Now if we would like to get hostnames by architecture we could compose queries by doing the following:
-- name: get_os_by_architecture
-- docs: Gets operative system's name by a given architecture.
SELECT name
FROM operative_system
WHERE architecture = :architecture
-- name: get_hostnames_by_architecture
-- docs: Gets hostnames by architecture.
SELECT hostname
FROM servers
WHERE os_name IN ( :get_os_by_architecture )
The previous query would generate the function
Queries.get_hostnames_by_architecture/2
that can be called as:
iex> Queries.get_hostnames_by_architecture(architecture: "AMD64")
{:ok,
[
%{hostname: "server0"},
%{hostname: "server1"},
...
]
}
Optional Parameters
Let's say that now we need to order ascending or descending by hostname by
using an optional :_order_by
parameter e.g:
-- name: get_os_by_architecture
-- docs: Gets operative system's name by a given architecture.
SELECT name
FROM operative_system
WHERE architecture = :architecture
-- name: get_hostnames_by_architecture
-- docs: Gets hostnames by architecture.
SELECT hostname
FROM servers
WHERE os_name IN ( :get_os_by_architecture )
:_order_by
-- name: ascending
ORDER BY hostname ASC
-- name: descending
ORDER BY hostname DESC
The previous query could be called as before:
iex> Queries.get_hostnames_by_architecture(architecture: "AMD64")
{:ok,
[
%{hostname: "Barcelona"},
%{hostname: "Granada"},
%{hostname: "Madrid"},
...
]
}
or by order ascending:
iex> params = [architecture: "AMD64", _order_by: :ascending]
iex> Queries.get_hostnames_by_architecture(params)
{:ok,
[
%{hostname: "Barcelona"},
%{hostname: "Madrid"},
%{hostname: "Granada"},
...
]
}
or descending:
iex> params = [architecture: "AMD64", _order_by: :descending]
iex> Queries.get_hostnames_by_architecture(params)
{:ok,
[
%{hostname: "Zaragoza"},
%{hostname: "Madrid"},
%{hostname: "Granada"},
...
]
}
Important: A query can be called by name e.g.
:descending
if it's defined in the same SQL file. Otherwise, we need to pass the function instead e.g.Queries.descending/2
iex> params = [architecture: "AMD64", _order_by: Queries.descending/2] iex> Queries.get_hostnames_by_architecture(params) {:ok, [ %{hostname: "Zaragoza"}, %{hostname: "Madrid"}, %{hostname: "Granada"}, ... ] }
IN
Statement
Lists in SQL might be tricky. That's why AyeSQL supports a special type for them e.g:
Let's say we have the following query:
-- name: get_os_by_hostname
-- docs: Gets hostnames and OS names given a list of hostnames.
SELECT hostname, os_name
FROM servers
WHERE hostname IN (:hostnames)
It is possible to do the following:
iex> params = [hostnames: {:in, ["server0", "server1", "server2"]}]
iex> Server.get_os_by_hostname(params)
{:ok,
[
%{hostname: "server0", os_name: "Debian Buster"},
%{hostname: "server1", avg_ram: "Windows 10"},
%{hostname: "server2", avg_ram: "Minix 3"}
]
}
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 Queries do
use AyeSQL, runner: IdemRunner, repository: MyRepo
defqueries("queries.sql")
end
or
import AyeSQL, only: [defqueries: 3]
defqueries(Queries, "queries.sql", runner: IdemRunner, repository: MyRepo)
For runners, there is only one callback to be implemented.
run/2
: which receives aAyeSQL.Query.t()
and akeyword()
list with extra options for the runner.
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
alias AyeSQL.Query
@impl true
def run(%Query{statement: stmt, arguments: args}, options) do
repo = options[:repository] || raise ArgumentError, "No repo defined"
Ecto.Adapters.SQL.query(repo, stmt, args)
end
end
Running Queries by Default
Queries are not run by default, but the AyeSQL.Query.t()
struct is returned
instead. For running queries by default, we can add the following to the
config:
use Mix.Config
config :ayesql,
run?: true
And then we don't need to specify the [run?: true]
options for every query.
Installation
AyeSQL
is available as a Hex package. To install, add it to your
dependencies in your mix.exs
file:
def deps do
[{:ayesql, "~> 0.5"}]
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.