Cornucopia

Generate type checked Rust from your SQL

Install | Example

Cornucopia is a small CLI utility resting on postgres designed to facilitate PostgreSQL workflows in Rust.

Cornucopia aims to get out of your way, transpiling your PostgreSQL queries to Rust on demand. Each query is prepared against your schema, ensuring that the query statements are valid SQL. These prepared statements are then be used to generate properly type-checked Rust code for this query.

Features

• SQL-first. Your database schema is the source of truth. No ORM.
• Custom user types (composites, enums and domains).
• Async (tokio_postgres) and sync drivers (postgres).
• Ergonomic type mapping.
• One-dimensional array types.
• Granular nullity control.
• Optional migration management.
• Build your queries against your own live database, or let Cornucopia manage that for you.
• Use the connection type that you want (pooled or not, transaction or not). You can mix and match them freely.
• Compatible with build scripts to generate whenever your SQL changes.

Keep reading for more info, or take a look at the basic example for a quickstart 🚀.

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Install

Container manager

Cornucopia spawns a postgres container when it generates your Rust modules, so, you'll need a working docker or podman command. Note: If you only work in live mode, you may not need a container manager since you'll manage the database yourself.

To use docker on Linux, non-sudo users need to be in the docker group. For a step-by-step guide, please read the official docker installation and post-installation docs.

No special installation steps are needed for podman, but note that you will need to pass a CLI flag to cornucopia (-p or --podman) as it defaults to docker.

Dependencies

Required

• Client code: cornucopia_client.
• Postgres type utils: postgres_types.

(Optional) Async

• Runtime: tokio.
• Database driver: tokio_postgres .
• Async tools: futures.

(Optional) Connection pooling

• Pooled connections: deadpool-postgres.

(Optional) Extra types using tokio_postgres features

Crate	available types	tokio_postgres feature
serde_json	Value	with-serde_json-1
time	Date Time PrimitiveDateTime OffsetDateTime	with-time-0_3
uuid	Uuid	with-uuid-1
eui48	MacAddress	with-eui48-1

Full dependencies

The code block below shows what your dependencies might look like with every feature that cornucopia supports enabled:

# Cargo.toml
[dependencies]
tokio = { version = "1.18.1", features = ["full"] }
deadpool-postgres = { version = "0.10.2" }
cornucopia_client = "0.2.2"
futures = "0.3.21"
tokio-postgres = { version = "0.7.6", features = [
    "with-serde_json-1",
    "with-time-0_3",
    "with-uuid-1",
    "with-eui48-1",
] }
serde = { version = "1.0.137", features = ["derive"] }
serde_json = "1.0.81"
time = "0.3.9"
uuid = "1.0.0"
eui48 = "1.1.0"

You can omit tokio-postgres feature flags for json, time, uuid, eui48 and their corresponding crates if you don't need them.

Cornucopia CLI

Aside from the code dependencies, you will need the cornucopia CLI to generate your Rust modules. This can be done via a simple cargo install cornucopia which will pull the latest binary and install it in your cargo path. Note that once the queries have been generated, they build and run standalone without requiring the CLI.

Concepts

This section explain a bit more about how Cornucopia works. If you just want to get started, you should take a look at the basic example.

Cornucopia is pretty simple to use. In the next sections, we'll explore the basic usage, but feel free to look the CLI's whole interface using the --help option at any point. For convenience, the CLI's reference document is also available in this repository.

Migrations

The basic cornucopia generate command creates a new container, runs your migrations, generates your queries and cleanups the container. If you want to manage the database and migrations yourself, use the cornucopia generate live command to connect to an arbitrary live database. Keep in mind that your queries must still be otherwise compatible with Cornucopia (e.g. with regards to supported types and annotation syntax).

New migrations can be added using the command cornucopia migration new.

Finally, as a convenience, you can use cornucopia migration run to run migrations on your database too if you so desire. This feature worksfor simple cases, but is not yet thoroughly tested and it's advisable that you use a more robust migration system.

Queries

Each .sql file in your queries directory will be converted into a Rust module containing your generated queries. Each query is actually prepared against your database, ensuring as many errors as possible will be caught before production. The generated functions are fully typed, giving you insight into your SQL and pretty strong guards against runtime errors.

Generated modules

Assuming you have the following migration

CREATE TABLE Author (
    Id SERIAL NOT NULL,
    Name VARCHAR(70) NOT NULL,
    Country VARCHAR(100) NOT NULL,
    PRIMARY KEY(Id)
);

and the following query

--! author_name_starting_with
SELECT
    *
FROM
    Author
WHERE
    name LIKE CONCAT(:start_str::text, '%');

After generating your queries with cornucopia, you could use it like this

let authors = author_name_starting_with(client, &"Joh").vec().await?;
// Print all the authors whose name starts with "Joh"
for author in authors {
  println!("{}" author.name)
}

The generated code covers lot more than that, but the above should be fairly representative how you could use the generated code. Head over to the examples if you want to see more features in action.

The diagram below shows a very high level representation of the items generated by Cornucopia. It's not exhaustive, but it can help you wrap your head around the generated code if you're starting out.

Query annotation syntax

--! example_query
select * from authors
where first_name = :first_name and last_name = :last_name

Notice that bind parameters are specified by name with the :colon_identifier notation, instead of by index. This allows queries to be very concise while also being more expressive.

Annotations are whitespace insignificant and can be split accross multiple lines too

--! authors (
--!
--! )

Comments that do not start with --! (e.g. -- This) are simply ignored by Cornucopia, so feel free to use them as you usually would.

Nullable columns

--! authors_named_john(first_name?): (name?)
select name from authors 
where first_name = :first_name

Query parameters and columns can specify their nullity by using the (hello?, world?) notation. Fields that are not present are assumed to be non-null.

Transactions

Generated queries take a GenericClient as parameter, which accepts both Clients and Transactions. That means you can use the same generated queries for both single statements and transactions.

Automatically generate queries

You can make use of Rust's build script feature to automatically regenerate your Cornucopia queries upon building your crate, only when your SQL has changed. The simplest way to achieve this is simply to call Cornucopia's CLI inside your build.rs file. You can learn more about this feature in this example.

Supported types

Base types

PostgrsQL type	Rust type
bool, boolean	bool
"char"	i8
smallint, int2, smallserial, serial2	i16
int, int4, serial, serial4	i32
bigint, int8, bigserial, serial8	i64
real, float4	f32
double precision, float8	f64
text	String
varchar	String
bytea	Vec<u8>
timestamp without time zone, timestamp	time::PrimitiveDateTime
timestamp with time zone, timestamptz	time::OffsetDateTime
date	time::Date
time	time::Time
json	serde_json::Value
jsonb	serde_json::Value
uuid	uuid::Uuid
inet	std::net::IpAddr
macaddr	eui48::MacAddress

Custom types

Cornucopia also supports user-defined enums, composites and domains. Just like base types, custom types will be generated automatically by inspecting your database. The only requirement for your custom types is that they be based on other supported types (base or custom). Cornucopia is also aware of your types' namespaces (what PostgreSQL calls schemas), so it will correctly handle custom types like my_schema.my_custom_type.

Array types

Cornucopia supports one-dimensionnal arrays for which the element type is also a type supported . That is, Cornucopia supports example_elem_type[] if example_elem_type is itself a type supported by Cornucopia (base or custom).

MSRV

This crate uses Rust 2021 edition, which requires at least version 1.56.

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT) at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.