Code shared from the Rust Playground

playground.rs

use std::path::Path;
use core::marker::PhantomData;
use core::borrow::Borrow;
use chrono::{DateTime, Utc, Days};
use rusqlite::{named_params, Connection, Statement};
use serde::{Serialize, Deserialize};
use thiserror::Error;


pub type Result<T, E = Error> = core::result::Result<T, E>;

#[derive(Debug, Error)]
pub enum Error {
    #[error("SQLite error: {0}")]
    SQLite(#[from] rusqlite::Error),
    #[error("SQL type conversion error: {0}")]
    FromSql(#[from] rusqlite::types::FromSqlError),
    #[error("invalid name `{0}`")]
    InvalidName(String),
    #[error("encoding error: {0}")]
    Encoding(#[from] serde_json::Error),
    #[error("value not found for key")]
    KeyNotFound,
}

pub struct Store {
    conn: Connection,
}

impl Store {
    pub fn open<P: AsRef<Path>>(path: P) -> Result<Self> {
        let conn = Connection::open(path)?;
        Ok(Store { conn })
    }
    
    pub fn collection<K, V>(&self, name: &str) -> Result<Collection<'_, K, V>> {
        if !name.chars().all(|ch| ch.is_ascii_alphanumeric() || ch == '_') {
            return Err(Error::InvalidName(name.to_owned()));
        }
        
        let create_sql = format!(
            r#"
            CREATE TABLE IF NOT EXISTS "{}"(
                "key" BLOB NOT NULL PRIMARY KEY,
                "value" BLOB NOT NULL,
                "expiry" REAL NULL -- NULL means never expires
            )"#,
            name
        );
        self.conn.execute(&create_sql, [])?;
        
        let get_sql = format!(
            r#"
            SELECT "value" AS "value"
            FROM "{}"
            WHERE
                "key" = :key
              AND
                ("expiry" IS NULL OR JULIANDAY() < "expiry")
            "#,
            name
        );
        let get_stmt = self.conn.prepare(&get_sql)?;
        
        let set_sql = format!(
            r#"
            INSERT OR REPLACE INTO "{}"("key", "value", "expiry")
            VALUES (:key, :value, JULIANDAY(:expiry))
            "#,
            name
        );
        let set_stmt = self.conn.prepare(&set_sql)?;

        let del_sql = format!(
            r#"
            DELETE FROM "{}"
            WHERE "key" = :key
            "#,
            name
        );
        let del_stmt = self.conn.prepare(&del_sql)?;
        
        let cln_sql = format!(
            r#"
            DELETE FROM "{}"
            WHERE
                "expiry" IS NOT NULL
              AND
                "expiry" < JULIANDAY()
            "#,
            name
        );
        let cln_stmt = self.conn.prepare(&cln_sql)?;
        
        Ok(Collection {
            get_stmt,
            set_stmt,
            del_stmt,
            cln_stmt,
            buf: Vec::new(),
            marker: PhantomData,
        })
    }
}

pub struct Collection<'store, K, V> {
    get_stmt: Statement<'store>,
    set_stmt: Statement<'store>,
    del_stmt: Statement<'store>,
    cln_stmt: Statement<'store>,
    buf: Vec<u8>,
    marker: PhantomData<fn() -> (K, V)>,
}

impl<'store, K, V> Collection<'store, K, V> {
    pub fn get<Q>(&mut self, key: &Q) -> Result<V>
    where
        K: Eq + Borrow<Q>,
        V: for<'de> Deserialize<'de>,
        Q: ?Sized + Eq + Serialize,
    {
        self.buf.clear();
        serde_json::to_writer(&mut self.buf, key.borrow())?;
        
        let mut rows = self.get_stmt.query(named_params!{":key": &self.buf[..]})?;
        let maybe_row = rows.next()?;
        let row = maybe_row.ok_or(Error::KeyNotFound)?;
        let bytes = row.get_ref("value")?.as_bytes()?;
        let value: V = serde_json::from_slice(bytes)?;
        
        Ok(value)
    }
    
    pub fn get_opt<Q>(&mut self, key: &Q) -> Result<Option<V>>
    where
        K: Eq + Borrow<Q>,
        V: for<'de> Deserialize<'de>,
        Q: ?Sized + Eq + Serialize,
    {
        self.buf.clear();
        serde_json::to_writer(&mut self.buf, key.borrow())?;
        
        let mut rows = self.get_stmt.query(named_params!{":key": &self.buf[..]})?;
        let row = match rows.next()? {
            Some(r) => r,
            None => return Ok(None),
        };
        let bytes = row.get_ref("value")?.as_bytes()?;
        let value: V = serde_json::from_slice(bytes)?;
        
        Ok(Some(value))
    }
    
    pub fn set<Q, U, E>(&mut self, key: &Q, value: &U, expiry: E) -> Result<()>
    where
        K: Eq + Borrow<Q>,
        V: Borrow<U>,
        Q: ?Sized + Eq + Serialize,
        U: ?Sized + Serialize,
        E: Into<Option<DateTime<Utc>>>,
    {
        self.buf.clear();
        serde_json::to_writer(&mut self.buf, key.borrow())?;
        let key_len = self.buf.len();
        
        serde_json::to_writer(&mut self.buf, value.borrow())?;
        let (key_bytes, value_bytes) = self.buf.split_at(key_len);
        
        self.set_stmt.execute(named_params!{
            ":key": key_bytes,
            ":value": value_bytes,
            ":expiry": expiry.into(),
        })?;
        
        Ok(())
    }
    
    pub fn remove<Q>(&mut self, key: &Q) -> Result<bool>
    where
        K: Eq + Borrow<Q>,
        Q: ?Sized + Eq + Serialize,
    {
        self.buf.clear();
        serde_json::to_writer(&mut self.buf, key.borrow())?;
        
        let num_rows = self.del_stmt.execute(named_params!{":key": &self.buf[..]})?;
        
        Ok(num_rows > 0)
    }
    
    /// remove expired entries
    pub fn cleanup(&mut self) -> Result<()> {
        self.cln_stmt.execute([])?;
        Ok(())
    }
}

#[derive(Clone, Copy, PartialEq, Eq, Debug, Serialize, Deserialize)]
enum Color {
    Red,
    Green,
    Blue,
}

#[derive(Clone, PartialEq, Eq, Debug, Serialize, Deserialize)]
struct User {
    handle: String,
    age: u32,
    favorite_color: Color,
}

fn main() -> Result<()> {
    let store = Store::open("/tmp/store.db")?;
    let mut coll: Collection<String, User> = store.collection("people")?;
    
    coll.set("foo", &User {
        handle: String::from("John Foo"),
        age: 63,
        favorite_color: Color::Red,
    }, Utc::now().checked_add_days(Days::new(1)))?; // expiry in 1 day
    coll.set("bar", &User {
        handle: String::from("Alice Bar"),
        age: 27,
        favorite_color: Color::Blue,
    }, None)?; // does not expire
    
    let u1 = coll.get("foo")?;
    dbg!(u1);
    
    let u2 = coll.get_opt("nonexistent")?;
    dbg!(u2);
    
    assert_eq!(coll.remove("bar")?, true);
    assert_eq!(coll.remove("something")?, false);
    
    Ok(())
}