postgres-mapper

postgres-mapper is a proc-macro designed to make mapping from postgresql tables to structs simple.

Why?

It can be frustrating to write a lot of boilerplate and, ultimately, duplicated code for mapping from postgres Rows into structs.

For example, this might be what someone would normally write:

extern crate postgres;

use postgres::rows::Row;

pub struct User {
    pub id: i64,
    pub name: String,
    pub email: Option<String>,
}

impl From<Row> for User {
    fn from(row: Row) -> Self {
        Self {
            id: row.get("id"),
            name: row.get("name"),
            email: row.get("email"),
        }
    }
}

// code to execute a query here and get back a row
let user = User::from(row); // this can panic

This becomes worse when manually implementating using the non-panicking get_opt method variant.

Using this crate, the boilerplate is removed, and panicking and non-panicking implementations are derived:

#[macro_use] extern crate postgres_mapper_derive;
extern crate postgres_mapper;

use postgres_mapper::FromPostgresRow;

#[derive(PostgresMapper)]
#[pg_mapper(table = "user")]
pub struct User {
    pub id: i64,
    pub name: String,
    pub email: Option<String>,
}

// Code to execute a query here and get back a row might now look like:
let stmt = "SELECT {$1} FROM {$2}
    WHERE username = {$3} AND password = {$4}";

let rows = &self
    .conn
    .query(
        stmt,
        &[&User::sql_fields(), &User::sql_table(), username, pass],
    ).unwrap();

let user = rows
    .iter()
    .next()
    .map(|row|
      // `postgres_mapper::FromPostgresRow`'s methods do not panic and return a Result
      User::from_postgres_row(row)?
    );

The two crates

This repository contains two crates: postgres-mapper which contains an Error enum and traits for converting from a postgres or tokio-postgres Row without panicking, and postgres-mapper-derive which contains the proc-macro.

postgres-mapper-derive has 3 features that can be enabled (where T is the struct being derived with the provided PostgresMapper proc-macro):

• postgres-support, which derives impl<'a> From<::postgres::rows::Row<'a>> for T and impl<'a> From<&'a ::postgres::Row<'a>> for T implementations
• tokio-postgres-support, which derives impl From<::tokio_postgres::rows::Row> for T and impl From<&::tokio_postgres::rows::Row> for T implementations
• postgres-mapper which, for each of the above features, implements postgres-mapper's FromPostgresRow and/or FromTokioPostgresRow traits

postgres-mapper has two features, postgres-support and tokio-postgres-support. When one is enabled in postgres-mapper-derive, it must also be enabled in postgres-mapper.

Installation

The above might be confusing, so here's an example where tokio-postgres is enabled in both crates:

Add the following to your Cargo.toml:

[dependencies.postgres-mapper]
features = ["tokio-postgres-support"]
version = "0.1"

[dependencies.postgres-mapper-derive]
features = ["postgres-mapper", "tokio-postgres-support"]
version = "0.1"

This will derive implementations for converting from owned and referenced tokio-postgres::rows::Rows, as well as implementing postgres-mapper's FromTokioPostgresRow trait for non-panicking conversions.

License

ISC.