**include-postgres-sql** is an extension of [include-sql][1] for using Postgres SQL in Rust. It completes include-sql by providing `impl_sql` macro to generate database access methods from the included SQL. include-postgres-sql uses [Rust-Postgres][2] for database access.
# Usage
Include `include-postgres-sql` as a dependency:
```toml
[dependencies]
include-postgres-sql = "0.1"
```
Write your SQL and save it in a file. For example, let's say the following is the content of the `library.sql` file that is saved in the project's `src` folder:
```sql
-- name: get_loaned_books?
-- Returns the list of books loaned to a patron
-- # Parameters
-- param: user_id: &str - user ID
SELECT book_title
FROM library
WHERE loaned_to = :user_id
ORDER BY 1;
-- name: loan_books!
-- Updates the book records to reflect loan to a patron
-- # Parameters
-- param: user_id: &str - user ID
-- param: book_ids: i32 - book IDs
UPDATE library
SET loaned_to = :user_id
, loaned_on = current_timestamp
WHERE book_id IN (:book_ids);
```
And then use it in Rust as:
```rust , ignore
use include_postgres_sql::{include_sql, impl_sql};
use postgres::{Config, NoTls, Error};
include_sql!("src/library.sql");
fn main() -> Result<(),Error> {
let args : Vec<String> = std::env::args().collect();
let user_id = &args[1];
let mut db = Config::new().host("localhost").connect(NoTls)?;
db.get_loaned_books(user_id, |row| {
let book_title : &str = row.try_get("book_title")?;
println!("{}", book_title);
Ok(())
})?;
Ok(())
}
```
> **Note** that the path to the SQL file must be specified relative to the project root, i.e. relative to `CARGO_MANIFEST_DIR`, even if you keep your SQL file alongside rust module that includes it. Because include-sql targets stable Rust this requirement will persist until [SourceFile][3] stabilizes.
# Anatomy of the Included SQL File
Please see the **Anatomy of the Included SQL File** in [include-sql][4] documentation for the description of the format that include-sql can parse.
# Generated Methods
**include-postgres-sql** generates 3 variants of database access methods using the following selectors:
* `?` - methods that process rows retrieved by `SELECT`,
* `!` - methods that execute all other non-`SELECT` methods, and
* `->` - methods that execute `RETURNING` statements and provide access to returned data.
## Process Selected Rows
For the `SELECT` statement like:
```sql
-- name: get_loaned_books?
-- param: user_id: &str
SELECT book_title FROM library WHERE loaned_to = :user_id;
```
The method with the following signature is generated:
```rust , ignore
fn get_loaned_books<F>(&self, user_id: &str, row_callback: F) -> Result<(),postgres::Error>
where F: Fn(postgres::Row) -> Result<(),postgres::Error>;
```
Where:
- `user_id` is a parameter that has the same name as the SQL parameter with the declared (in the SQL) type as `&str`.
- `F` is a type of a callback (closure) that the method implementation will call to process each row.
## Execute Non-Select Statements
For non-select statements - INSERT, UPDATE, DELETE, etc. - like the following:
```sql
-- name: loan_books!
-- param: user_id: &str
-- param: book_ids: i32
UPDATE library
SET loaned_to = :user_id
, loaned_on = current_timestamp
WHERE book_id IN (:book_ids);
```
The method with the following signature is generated:
```rust , ignore
fn loan_books(&self, user_id: &str, book_ids: &[i32]) -> Result<u64,postgres::Error>;
```
Where:
- `user_id` is a parameter that has the same name as the SQL parameter with the declared (in the SQL) type as `&str`,
- `book_ids` is a parameter for the matching IN-list parameter where each item in a collection has type `u32`.
## RETURNING Statements
For DELETE, INSERT, and UPDATE statements that return data via `RETURNING` clause like:
```sql
-- name: add_new_book->
-- param: isbn: &str
-- param: book_title: &str
INSERT INTO library (isbn, book_title)
VALUES (:isbn, :book_title)
RETURNING book_id;
```
The method with the following signature is generated:
```rust , ignore
fn add_new_book(&self, isbn: &str, book_title: &str) -> Result<postgres::Row,postgres::Error>;
```
# Inferred Parameter Types
If a statement parameter type is not explicitly specified via `param:`, **include-postgres-sql** will use `impl postgres::types::ToSql` for the corresponding method parameters. For example, if the SQL from the example above has not provided its parameter type:
```sql
-- name: get_loaned_books?
-- Returns the list of books loaned to a patron
SELECT book_title
FROM library
WHERE loaned_to = :user_id
ORDER BY 1;
```
Then the signature of the generated method would be:
```rust , ignore
/// Returns the list of books loaned to a patron
fn get_loaned_books<F>(&self, user_id: impl postgres::types::ToSql, row_callback: F) -> Result<(),postgres::Error>
where F: Fn(postgres::Row) -> Result<(),postgres::Error>;
```
[1]: https://crates.io/crates/include-sql
[2]: https://crates.io/crates/postgres
[4]: https://doc.rust-lang.org/proc_macro/struct.SourceFile.html
[3]: https://quietboil.github.io/include-sql