Crate include_postgres_sql

Expand description

include-postgres-sql is an extension of include-sql 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 for database access.

§Features

include-postgres-sql has a single feature - tokio - which, when selected, makes include-postgres-sql generate async databases access methods that can be used with tokio-postgres.

§Usage

Add include-postgres-sql and postgres as a dependency:

[dependencies]
include-postgres-sql = "0.2"
postgres = "0.19"

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 sql folder:

-- 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: book_titles: &str - book titles
-- param: user_id: &str - user ID
--
UPDATE library
   SET loaned_to = :user_id
     , loaned_on = current_timestamp
 WHERE book_title IN (:book_titles)

And then use it in Rust as:

use postgres::{Config, NoTls, Error};
use include_postgres_sql::{include_sql, impl_sql};

include_sql!("sql/library.sql");

fn main() -> Result<(),Error> {
    let mut db = Config::new().host("localhost").connect(NoTls)?;

    db.loan_books(&["War and Peace", "Gone With the Wind"], "Sheldon Cooper")?;

    db.get_loaned_books("Sheldon Cooper", |row| {
        let book_title : &str = row.try_get(0)?;
        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 stabilizes.

§Async

Add the following dependencies:

[dependencies]
include-postgres-sql = { version = "0.2", features = ["tokio"] }
tokio-postgres = "0.7"
tokio = { version = "1", features = ["full"] }

Note full tokio features are not required. tokio dependency is listed like that for illustration only.

The same SQL as above can then be used in async Rust as:

use include_postgres_sql::{include_sql, impl_sql};
use tokio_postgres::{Config, NoTls, Error};

include_sql!("sql/library.sql");

#[tokio::main]
async fn main() -> Result<(),Error> {
    let (db, conn) = Config::new().host("localhost").connect(NoTls).await?;
    tokio::spawn(async move {
        if let Err(e) = conn.await {
            eprintln!("connection error: {}", e);
        }
    });

    db.loan_books(&["War and Peace", "Gone With the Wind"], "Sheldon Cooper").await?;

    db.get_loaned_books("Sheldon Cooper", |row| {
        let book_title : &str = row.try_get(0)?;
        println!("{book_title}");
        Ok(())
    }).await?;

    Ok(())
}

§Anatomy of the Included SQL File

Please see the Anatomy of the Included SQL File in include-sql documentation for the description of the format that include-sql can parse.

§Generated Methods

include-postgres-sql generates 5 variants of database access methods using the following selectors:

? - methods that process rows retrieved by SELECT,
^ - methods that return rows retrieved by SELECT (as postgres::RowIter or tokio_postgres::RowStream ),
% - methods that extract data from selected rows into row specific structs and return them as Vec,
! - methods that execute all other non-SELECT methods, and
-> - methods that execute RETURNING statements and provide access to returned data.

§Process Selected Rows

§Callback

For the SELECT statement like:

-- 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:

fn get_loaned_books<F>(&self, user_id: &str, row_callback: F) -> Result<(),postgres::Error>
where F: FnMut(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.

§Row Iterator

When the same SELECT statement is tagged as ^:

-- name: get_loaned_books^
-- param: user_id: &str
SELECT book_title FROM library WHERE loaned_to = :user_id

Then a regular postgres variant of the generated method will have the following signature:

fn get_loaned_books<'a>(&'a self, user_id: &str) -> Result<postgres::RowIter<'a>,postgres::Error>;

§Row Stream

For the same - tagged as ^ - SELECT statement for the tokio-postgres variant, i.e. when tokio feature is used, of the generated method will have the following signature:

async fn get_loaned_books(&self, user_id: &str) -> Result<tokio_postgres::RowStream,tokio_postgres::Error>;

§Vector

When the same SELECT statement is tagged as %:

-- name: get_loaned_books%
-- param: user_id: &str
SELECT isbn, book_title FROM library WHERE loaned_to = :user_id

Then a regular postgres variant of the generated method will have the following signature:

fn get_loaned_books<R>(&self, user_id: &str) -> Result<Vec<R>,postgres::Error>
where R: TryFrom<postgres::Row>, postgres::Error: From<R::Error>;

It requires a struct defines that is capable deserializing a returned Row. For example, to deserialize the rows from the above query the following struct can be defined:

struct LoanedBook {
    isbn: String,
    title: String,
}

impl TryFrom<postgres::Row> for LoanedBook {
    type Error = postgres::Error;

    fn try_from(row: postgres::Row) -> Result<Self, Self::Error> {
        let isbn  = row.try_get(0)?;
        let title = row.try_get(1)?;
        Ok(Self {isbn, title})
    }
}

Then the entire result set can be retrieved as:

let loaned_books : Vec<LoanedBook> = db.get_loaned_books(user_id)?;

§Execute Non-Select Statements

For non-select statements - INSERT, UPDATE, DELETE, etc. - like the following:

-- name: loan_books!
-- param: book_titles: &str
-- param: user_id: &str
UPDATE library
   SET loaned_to = :user_id
     , loaned_on = current_timestamp
 WHERE book_titles IN (:book_titles)

The method with the following signature is generated:

fn loan_books(&self, user_id: &str, book_titles: &[&str]) -> Result<u64,postgres::Error>;

Where:

book_titles is a parameter for the matching IN-list parameter where each item in a collection has type &str.
user_id is a parameter that has the same name as the SQL parameter with the declared (in the SQL) type as &str,

§RETURNING Statements

For DELETE, INSERT, and UPDATE statements that return data via RETURNING clause like:

-- 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:

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 scalar method parameters. For example, if the SQL from the example above has not provided its parameter type:

-- name: get_loaned_books?
SELECT book_title
  FROM library
 WHERE loaned_to = :user_id
 ORDER BY 1

Then the signature of the generated method would be:

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>;

For the “IN list” type of parameters include-postgres-sql will generate a method parameter as a slice where each element is the same generic type supplied by include-sql:

-- name: loan_books!
UPDATE library
   SET loaned_to = :user_id
     , loaned_on = current_timestamp
 WHERE book_titles IN (:book_titles)

The signature of the generated method would be:

fn loan_books<BookTitles: postgres::types::ToSql>(&self, 
    user_id: impl postgres::types::ToSql, 
    book_titles: &[BookTitles]
) -> Result<u64,postgres::Error>;

§Examples

include-postgres-sql integration tests are written as tiny applications that can be used as examples of various usages of included SQL.

Macros§

impl_sql: Generates Rust code to use included SQL.
include_sql: Reads and parses the specified SQL file, and generates impl_sql macro call.