Working with Postgres

Create tables in a Postgres database

Use the postgres crate to create tables in a Postgres database.

Client::connect helps in connecting to an existing database. The recipe uses a URL string format with Client::connect. It assumes an existing database named library, the username is postgres and the password is postgres.

use postgres::{Client, NoTls, Error};

fn main() -> Result<(), Error> {
    let mut client = Client::connect("postgresql://postgres:postgres@localhost/library", NoTls)?;
    
    client.batch_execute("
        CREATE TABLE IF NOT EXISTS author (
            id              SERIAL PRIMARY KEY,
            name            VARCHAR NOT NULL,
            country         VARCHAR NOT NULL
            )
    ")?;

    client.batch_execute("
        CREATE TABLE IF NOT EXISTS book  (
            id              SERIAL PRIMARY KEY,
            title           VARCHAR NOT NULL,
            author_id       INTEGER NOT NULL REFERENCES author
            )
    ")?;

    Ok(())

}

Insert and Query data

The recipe inserts data into the author table using execute method of Client. Then, displays the data from the author table using query method of Client.

use postgres::{Client, NoTls, Error};
use std::collections::HashMap;

struct Author {
    _id: i32,
    name: String,
    country: String
}

fn main() -> Result<(), Error> {
    let mut client = Client::connect("postgresql://postgres:postgres@localhost/library", 
                                    NoTls)?;
    
    let mut authors = HashMap::new();
    authors.insert(String::from("Chinua Achebe"), "Nigeria");
    authors.insert(String::from("Rabindranath Tagore"), "India");
    authors.insert(String::from("Anita Nair"), "India");

    for (key, value) in &authors {
        let author = Author {
            _id: 0,
            name: key.to_string(),
            country: value.to_string()
        };

        client.execute(
                "INSERT INTO author (name, country) VALUES ($1, $2)",
                &[&author.name, &author.country],
        )?;
    }

    for row in client.query("SELECT id, name, country FROM author", &[])? {
        let author = Author {
            _id: row.get(0),
            name: row.get(1),
            country: row.get(2),
        };
        println!("Author {} is from {}", author.name, author.country);
    }

    Ok(())

}

Aggregate data

This recipe lists the nationalities of the first 7999 artists in the database of the Museum of Modern Art in descending order.

use postgres::{Client, Error, NoTls};

struct Nation {
    nationality: String,
    count: i64,
}

fn main() -> Result<(), Error> {
    let mut client = Client::connect(
        "postgresql://postgres:postgres@127.0.0.1/moma",
        NoTls,
    )?;

    for row in client.query 
    ("SELECT nationality, COUNT(nationality) AS count 
    FROM artists GROUP BY nationality ORDER BY count DESC", &[])? {
        
        let (nationality, count) : (Option<String>, Option<i64>) 
        = (row.get (0), row.get (1));
        
        if nationality.is_some () && count.is_some () {

            let nation = Nation{
                nationality: nationality.unwrap(),
                count: count.unwrap(),
        };
            println!("{} {}", nation.nationality, nation.count);
            
        }
    }

    Ok(())
}