🐿️ Squirrelix — type-safe SQL in Elixir

Squirrelix (package squirr_elix)

Squirrelix turns plain .sql files into typed Elixir modules. You write one query per file; the generator discovers those files, resolves parameter and return types, and writes a sibling sql.ex module with @spec-annotated functions that run the queries through Postgrex.

It targets Elixir 1.20 and uses native typespecs rather than custom ADTs or Gleam-style records. See the Gleam Squirrel project for the upstream SQL discovery, inference, and query conventions that Squirrelix follows.

What's Squirrelix?

If you need to talk with a database in Elixir you'll often write something like this:

def find_user(conn, id) do
  Postgrex.query!(
    conn,
    "select name, age from users where id = $1",
    [id]
  )
  |> Map.fetch!(:rows)
  |> Enum.map(fn [name, age] -> %{name: name, age: age} end)
end

This is probably fine if you have a few small queries but it can become quite the burden when you have a lot of queries:

• The SQL query you write is just a plain string. You do not get syntax highlighting, auto formatting, suggestions... all the little niceties you would otherwise get if you were writing a plain *.sql file.
• This also means you lose the ability to run these queries on their own with other external tools, inspect them and so on.
• You have to manually keep row decoding in sync with the query's output.

One might be tempted to hide all of this by reaching for something like an ORM. Squirrelix proposes a different approach: instead of trying to hide the SQL it embraces it and leaves you in control. You write the SQL queries in plain old *.sql files and Squirrelix will take care of generating all the corresponding functions.

Instead of the hand-written example shown earlier you can instead just write the following query:

-- lib/my_app/accounts/sql/find_user.sql
-- Find a user and their age given their id.
select
  name,
  age
from
  users
where
  id = $1

And run mix squirrelix.gen --infer. Just like magic you'll now have a type-safe function find_user/2 you can use just as you'd expect:

alias MyApp.Accounts.SQL

{:ok, conn} = Postgrex.start_link(database: "my_app_dev")

# And it just works as you'd expect:
rows = SQL.find_user(conn, 42)
# => [%{name: "Ada", age: 36}]

Behind the scenes Squirrelix generates the decode helpers and functions you need; and it's pretty-printed, standard Elixir code. So now you get the best of both worlds:

• You don't have to take care of keeping encoders and decoders in sync — Squirrelix does that for you.
• And you're not compromising on type safety either: Squirrelix is able to understand the types of your query and produce correct @specs and runtime decoders.
• You can stick to writing plain SQL in *.sql files. You'll have better editor support, syntax highlighting and completions.
• You can run each query on its own: need to explain a query? No big deal, it's just a plain old *.sql file.

Requirements

• Elixir ~> 1.20
• Postgrex ~> 0.22 (for generated query modules and optional --infer mode)
• PostgreSQL >= 16 (when using --infer mode)

Installation

Add Squirrelix as a dev/test dependency (codegen Mix tool) and keep Postgrex as a runtime dependency for generated query modules:

def deps do
  [
    {:squirr_elix, "~> 0.1.0", only: [:dev, :test], runtime: false},
    {:postgrex, "~> 0.22"}
  ]
end

only: [:dev, :test] keeps the generator out of production while still available for mix squirrelix.check in CI. runtime: false prevents starting it with your app.

Then fetch dependencies:

mix deps.get

Documentation is published at https://hexdocs.pm/squirr_elix. Browse module docs locally with mix docs.

Quick start

Squirrelix discovers queries under conventional Elixir source roots. Put one SQL query per file inside a sql/ directory:

├── lib
│   ├── my_app
│   │   └── accounts
│   │       ├── sql
│   │       │   ├── find_user.sql
│   │       │   └── list_users.sql
│   │       └── sql.ex          # generated: MyApp.Accounts.SQL
│   └── my_app.ex
└── mix.exs

Generate typed query modules by connecting to Postgres and inferring types:

mix squirrelix.gen --infer --database my_app_dev

Each sql/ directory becomes one Elixir module named from your app and path — for example, lib/my_app/accounts/sql/ generates MyApp.Accounts.SQL. Each .sql file becomes a function named after the file (without the extension).

Verify generated code is current in CI:

mix squirrelix.check --infer --database my_app_dev

See the Getting Started guide for a full walkthrough.

Writing SQL queries

Squirrelix follows a small set of conventions:

• Squirrelix looks for all sql/ directories under your project's lib/, test/, and dev/ roots and reads all the *.sql files in there (in glob terms {lib,test,dev}/**/sql/*.sql).
• Each sql/ directory is turned into a single Elixir module containing a function for each *.sql file inside it. The generated module is located next to the corresponding sql/ directory and is named sql.ex.
• Each *.sql file must contain a single SQL query. The name of the file is the name of the corresponding Elixir function to run that query.
• Leading SQL comments (-- ...) become @doc strings on the generated functions.

Example. Given the project layout above, running mix squirrelix.gen --infer creates lib/my_app/accounts/sql.ex defining two functions — find_user/2 and list_users/1 — that you can import and use in your code.

See the Writing Queries guide for naming rules, comment conventions, and tips for nullable parameters.

Generated code overview

For each query Squirrelix generates:

• A per-query row @type (PascalCase of the function name + _row) describing the returned map shape.
• An @spec on the function with a Postgrex.conn() connection argument followed by inferred parameter types.
• A function body that prepares the query, encodes parameters, executes through Postgrex, and decodes rows into maps.

Example generated output:

@type find_user_row :: %{
  required(:name) => String.t(),
  required(:age) => integer()
}

@doc """
Find a user and their age given their id.
"""
@spec find_user(Postgrex.conn(), integer()) :: [find_user_row()]
def find_user(conn, id) do
  # ...
end

Row-returning queries produce [map()]. Command queries (for example insert, update, or delete with no returning clause) return :ok.

Generated modules include a runtime helpers section with shared encode/decode functions. You should treat sql.ex as generated code — edit the .sql files and re-run mix squirrelix.gen instead of editing the Elixir module directly.

CLI commands

Squirrelix offers the following Mix tasks to streamline your workflow:

• mix squirrelix.gen — Generates typed Elixir code for all SQL queries found under {lib,test,dev}/**/sql/*.sql.
• mix squirrelix.check — Validates that the generated Elixir code is up-to-date with the SQL queries. This is particularly useful to run in a CI pipeline to make sure you don't forget to run mix squirrelix.gen.

Both tasks accept the same options. See Configuration for metadata files, connection settings, and programmatic use.

mix squirrelix.gen --infer --database my_app_dev
mix squirrelix.check --infer --database my_app_dev

Query sources

Generation and checking accept a query source — either static metadata or a live Postgres inferrer:

Metadata file — keys are absolute or project-relative paths to .sql files; values are keyword lists with :params and :returns. Load one from squirr_elix.exs in the project root (or pass --metadata PATH):

# squirr_elix.exs
%{
  "lib/my_app/accounts/sql/find_user.sql" => [
    params: [:integer],
    returns: [
      %{name: "name", type: :string, nullable?: false},
      %{name: "age", type: :integer, nullable?: false}
    ]
  ]
}

mix squirrelix.gen
mix squirrelix.gen --metadata config/squirr_elix.exs

Postgres inferrer — connects to a database, prepares each query, and reads parameter and column types from Postgrex. Pass connection options on the CLI or via PG* environment variables:

mix squirrelix.gen --infer --database my_app_dev
mix squirrelix.gen --infer --url postgres://localhost/my_app_dev

The programmatic API mirrors this split — see Squirrelix.generate/3 and Squirrelix.check/3.

Configuration and connection

In order to understand the type of your queries, Squirrelix needs to connect to the Postgres server where the database schema is defined when you use --infer.

Pass a connection URL on the CLI (prefer PGPASSWORD over embedding passwords in the URL or --password):

mix squirrelix.gen --infer --url postgres://user@host:5432/database?connect_timeout=5

Or set Postgres environment variables. When a value is not set, Squirrelix uses these defaults:

You can also pass individual flags: --hostname, --port, --username, --password, and --database. Precedence (highest first): CLI flags → --url → environment → defaults.

Generated functions call Postgrex.query!/3 and raise on database errors. Metadata files are evaluated Elixir — only load trusted paths.

See the Configuration guide for metadata mode, the programmatic API, and CI setup.

Supported types

Squirrelix takes care of the mapping between Postgres types and Elixir types. This is needed in two places:

• Elixir values need to be encoded into Postgres values when you're filling in the holes of a prepared statement ($1, $2, ...).
• Postgres values need to be decoded into Elixir ones when you're reading the rows returned by a query.

The types that are currently supported are:

See the Types guide for nullable columns, JSON columns, and intentional differences from Gleam Squirrel.

Enums

If your queries deal with user-defined Postgres enums, Squirrelix maps them to String.t() in generated @specs. Enum labels are passed through at runtime as plain strings — Squirrelix does not generate Elixir enum modules or Gleam-style custom types.

For example, given this enum:

create type squirrel_colour as enum (
  'light_brown',
  'grey',
  'red'
);

A column of type squirrel_colour is typed as String.t() and decoded as "light_brown", "grey", or "red".

FAQ

What flavour of SQL does Squirrelix support?

Squirrelix only supports Postgres. It supports all versions >= 16.

Why isn't Squirrelix configurable in any way?

By going the "convention over configuration" route, Squirrelix enforces that all projects adopting it will always have the same structure. If you need to contribute to a project using Squirrelix you'll immediately know which directories and modules to look for.

This makes it easier to get started with a new project and cuts down on bike shedding: "Where should I put my queries?", "How many queries should go in one file?", ...

Can Squirrelix read my .env file?

The approach we recommend is either use your shell's built-in functionality for loading environment variables or use a convenience tool which builds upon that capability, such as direnv. This way the environment is managed by the environment rather than the application itself.

How do I deal with nullable query parameters?

Squirrelix works by inspecting the data that Postgres itself exposes about a query. Postgres doesn't expose any data about the nullability of query parameters, so Squirrelix can't generate the correct nullable type when, for example, inserting into a nullable column.

See the Writing Queries guide for recommended workarounds.

Errors and troubleshooting

Squirrelix reports structured errors during generation and checking. Common cases:

Connection failures during --infer produce a Mix error with the underlying Postgrex reason. Verify PG* variables or --url, ensure Postgres is running, and confirm the database exists and has the expected schema.

Relationship to Gleam Squirrel

Squirrelix is an Elixir port of Gleam Squirrel by Giacomo Cavalieri. It follows upstream query conventions — one query per file, sql/ directory layout, comment-to-doc mapping, parameter name inference, and Postgres type inference — while producing idiomatic Elixir output:

• Row results are plain maps, not Gleam records.
• Types use stdlib typespecs (String.t(), integer(), map() with required/1).
• Postgres enums map to String.t(), not generated enum ADTs.
• Generated modules use Postgrex, not pog.

Both projects are licensed under Apache 2.0. See LICENSE and NOTICE for attribution.

This package also draws inspiration from yesql and sqlx.

Development

Clone the repository and run the full validation suite before committing:

mix precommit

(mix precommit runs mix format, mix credo --strict --all, and mix test.)

See ROADMAP.md for completed work and remaining compatibility slices.

Guides

• Getting Started
• Writing Queries
• Types
• Configuration

License

Squirrelix is licensed under the Apache License 2.0. See LICENSE.