georm/src/lib.rs

//! # Georm
//!
//! ## Introduction
//!
//! Georm is a simple, opinionated SQLx ORM for PostgreSQL.
//!
//! To automatically implement the `Georm` trait, you need at least:
//! - to derive the `Georm` and `sqlx::FromRow` traits
//! - use the `georm` proc-macro to indicate the table in which your entity
//!   lives
//! - use the `georm` proc-macro again to indicate which field of your struct is
//!   the identifier of your entity.
//!
//! ## Simple usage
//! Here is a minimal use of Georm with a struct:
//!
//! ```ignore
//! #[derive(sqlx::FromRow, Georm)]
//! #[georm(table = "users")]
//! pub struct User {
//!     #[georm(id)]
//!     id: i32,
//!     username: String,
//!     hashed_password: String,
//! }
//! ```
//!
//! The `User` type will now have access to all the functions declared in the
//! `Georm` trait.
//!
//! ## One-to-one relationships
//!
//! You can then create relationships between different entities. For instance,
//! you can use an identifier of another entity as a link to that other entity.
//!
//! ```ignore
//! #[derive(sqlx::FromRow, Georm)]
//! #[georm(table = "profiles")]
//! pub struct Profile {
//!     #[georm(id)]
//!     id: i32,
//!     #[georm(
//!         relation = {
//!             entity = User,
//!             name = "user",
//!             table = "users",
//!             remote_id = "id",
//!             nullable = false
//!         })
//!     ]
//!     user_id: i32,
//!     display_name: String,
//! }
//! ```
//!
//! This will give access to the `Profile::get_user(&self, pool: &sqlx::PgPool)
//! -> User` method.
//!
//! Here is an explanation of what these different values mean:
//!
//! | Value Name | Explanation                                                                             | Default value |
//! |------------|-----------------------------------------------------------------------------------------|---------------|
//! | entity     | Rust type of the entity found in the database                                           | N/A           |
//! | name       | Name of the remote entity within the local entity; generates a method named `get_{name}` | N/A           |
//! | table      | Database table where the entity is stored                                               | N/A           |
//! | remote_id  | Name of the column serving as the identifier of the entity                              | `"id"`        |
//! | nullable   | Whether the relationship can be broken                                                  | `false`       |
//!
//! Note that in this instance, the `remote_id` and `nullable` values can be
//! omitted as this is their default value. This below is a strict equivalent:
//!
//! ```ignore
//! #[derive(sqlx::FromRow, Georm)]
//! #[georm(table = "profiles")]
//! pub struct Profile {
//!     #[georm(id)]
//!     id: i32,
//!     #[georm(relation = { entity = User, table = "users", name = "user" })]
//!     user_id: i32,
//!     display_name: String,
//! }
//! ```
//!
//! ## One-to-many relationships
//!
//! Sometimes, our entity is the one being referenced to by multiple entities,
//! but we have no internal reference to these remote entities in our local
//! entity. Fortunately, we have a way to indicate to Georm how to find these.
//!
//! ```ignore
//! #[derive(sqlx::FromRow, Georm)]
//! #[georm(table = "posts")]
//! struct Post {
//!     #[georm(id)]
//!     id: i32,
//!     #[georm(relation = { entity = User, table = "users", name = "user" })]
//!     author_id: i32,
//!     content: String
//! }
//!
//! #[derive(sqlx::FromRow, Georm)]
//! #[georm(
//!     table = "users",
//!     one_to_many = [{
//!         entity    = Post,
//!         name      = "posts",
//!         table     = "posts",
//!         remote_id = "id"
//!     }]
//! )]
//! struct User {
//!     #[georm(id)]
//!     id: i32,
//!     username: String,
//!     hashed_password: String
//! }
//! ```
//!
//! As we’ve seen earlier, the struct `Post` has access to the method
//! `Post::get_user(&self, pool: &sqlx::PgPool) -> User` thanks to the
//! proc-macro used on `author_id`. However, `User` now has also access to
//! `User::get_posts(&self, pool: &sqlx::PgPool) -> Vec<Post>`. And as you can
//! see, `one_to_many` is an array, meaning you can define several one-to-many
//! relationships for `User`.
//!
//! Here is an explanation of the values of `one_to_many`:
//!
//! | Value Name | Explanaion                                                                               | Default Value |
//! |------------|------------------------------------------------------------------------------------------|---------------|
//! | entity     | Rust type of the entity found in the database                                            | N/A           |
//! | name       | Name of the remote entity within the local entity; generates a method named `get_{name}` | N/A           |
//! | table      | Database table where the entity is stored                                                | N/A           |
//! | remote_id  | Name of the column serving as the identifier of the entity                               | `"id"`        |
//!
//! As with one-to-one relationships, `remote_id` is optional. The following
//! `User` struct is strictly equivalent.
//!
//! ```ignore
//! #[derive(sqlx::FromRow, Georm)]
//! #[georm(
//!     table = "users",
//!     one_to_many = [{ entity = Post, name = "posts", table = "posts" }]
//! )]
//! struct User {
//!     #[georm(id)]
//!     id: i32,
//!     username: String,
//!     hashed_password: String
//! }
//! ```
//!
//! ## Many-to-many relationships
//!
//! Many-to-many relationships between entities A and entities B with Georm rely
//! on a third table which refers to both. For instance, the following SQL code
//! describes a many-to-many relationship between books and book genre.
//!
//! ```sql
//! CREATE TABLE books (
//!     id SERIAL PRIMARY KEY,
//!     title VARCHAR(100) NOT NULL
//! );
//!
//! CREATE TABLE genres (
//!     id SERIAL PRIMARY KEY,
//!     name VARCHAR(100) NOT NULL
//! );
//!
//! CREATE TABLE books_genres (
//!     book_id INT NOT NULL,
//!     genre_id INT NOT NULL,
//!     PRIMARY KEY (book_id, genre_id),
//!     FOREIGN KEY (book_id) REFERENCES books(id) ON DELETE CASCADE,
//!     FOREIGN KEY (genre_id) REFERENCES genres(id) ON DELETE CASCADE
//! );
//! ```
//!
//! The table `books_genres` is the one defining the many-to-many relationship
//! between the table `books` and the table `genres`. With Georm, this gives us
//! the following code:
//!
//! ```ignore
//! #[derive(sqlx::FromRow, Georm)]
//! #[georm(
//!     table = "books",
//!     many_to_many = [{
//!         name = "genres",
//!         entity = Genre,
//!         table = "genres",
//!         remote_id = "id",
//!         link = { table = "books_genres", from = "book_id", to = "genre_id" }
//!     }]
//! )]
//! struct Book {
//!     #[georm(id)]
//!     id: i32,
//!     title: String
//! }
//!
//! #[derive(sqlx::FromRow, Georm)]
//! #[georm(
//!     table = "genres",
//!     many_to_many = [{
//!         entity = Book,
//!         name = "books",
//!         table = "books",
//!         remote_id = "id",
//!         link = { table = "books_genres", from = "genre_id", to = "book_id" }
//!     }]
//! )]
//! struct Genre {
//!     #[georm(id)]
//!     id: i32,
//!     name: String
//! }
//! ```
//!
//! This generates two methods:
//! - `Book::get_genres(&self, pool: &sqlx::PgPool) -> Vec<Genre>`
//! - `Genre::get_books(&self, pool: &sqlx::PgPool) -> Vec<Book>`
//!
//! As you can see, `many_to_many` is also an array, meaning we can define
//! several many-to-many relationships for the same struct.
//!
//! Here is an explanation of the values behind `many_to_many`:
//!
//! | Value Name | Explanation                                                                              | Default value |
//! |------------|------------------------------------------------------------------------------------------|---------------|
//! | entity     | Rust type of the entity found in the database                                            | N/A           |
//! | name       | Name of the remote entity within the local entity; generates a method named `get_{name}` | N/A           |
//! | table      | Database table where the entity is stored                                                | N/A           |
//! | remote_id  | Name of the column serving as the identifier of the entity                               | `"id"`        |
//! | link.table | Name of the many-to-many relationship table                                              | N/A           |
//! | link.from  | Column of the linking table referring to this entity                                     | N/A           |
//! | link.to    | Column of the linking table referring to the remote entity                               | N/A           |
//!
//! ## Limitations
//! ### Database
//!
//! For now, Georm is limited to PostgreSQL. Other databases may be supported in
//! the future, such as Sqlite or MySQL, but that is not the case yet.
//!
//! ## Identifiers
//!
//! Identifiers, or primary keys from the point of view of the database, may
//! only be simple types recognized by SQLx. They also cannot be arrays, and
//! optionals are only supported in one-to-one relationships when explicitly
//! marked as nullables.

pub use georm_macros::Georm;

pub trait Georm<Id> {
    /// Find all the entities in the database.
    ///
    /// # Errors
    /// Returns any error Postgres may have encountered
    fn find_all(
        pool: &sqlx::PgPool,
    ) -> impl ::std::future::Future<Output = ::sqlx::Result<Vec<Self>>> + Send
    where
        Self: Sized;

    /// Find the entiy in the database based on its identifier.
    ///
    /// # Errors
    /// Returns any error Postgres may have encountered
    fn find(
        pool: &sqlx::PgPool,
        id: &Id,
    ) -> impl std::future::Future<Output = sqlx::Result<Option<Self>>> + Send
    where
        Self: Sized;

    /// Create the entity in the database.
    ///
    /// # Errors
    /// Returns any error Postgres may have encountered
    fn create(
        &self,
        pool: &sqlx::PgPool,
    ) -> impl std::future::Future<Output = sqlx::Result<Self>> + Send
    where
        Self: Sized;

    /// Update an entity with a matching identifier in the database.
    ///
    /// # Errors
    /// Returns any error Postgres may have encountered
    fn update(
        &self,
        pool: &sqlx::PgPool,
    ) -> impl std::future::Future<Output = sqlx::Result<Self>> + Send
    where
        Self: Sized;

    /// Update an entity with a matching identifier in the database if
    /// it exists, create it otherwise.
    ///
    /// # Errors
    /// Returns any error Postgres may have encountered
    fn create_or_update(
        &self,
        pool: &sqlx::PgPool,
    ) -> impl ::std::future::Future<Output = sqlx::Result<Self>>
    where
        Self: Sized,
    {
        async {
            if Self::find(pool, self.get_id()).await?.is_some() {
                self.update(pool).await
            } else {
                self.create(pool).await
            }
        }
    }

    /// Delete the entity from the database if it exists.
    ///
    /// # Returns
    /// Returns the amount of rows affected by the deletion.
    ///
    /// # Errors
    /// Returns any error Postgres may have encountered
    fn delete(
        &self,
        pool: &sqlx::PgPool,
    ) -> impl std::future::Future<Output = sqlx::Result<u64>> + Send;

    /// Delete any entity with the identifier `id`.
    ///
    /// # Returns
    /// Returns the amount of rows affected by the deletion.
    ///
    /// # Errors
    /// Returns any error Postgres may have encountered
    fn delete_by_id(
        pool: &sqlx::PgPool,
        id: &Id,
    ) -> impl std::future::Future<Output = sqlx::Result<u64>> + Send;

    /// Returns the identifier of the entity.
    fn get_id(&self) -> &Id;
}