如何将 PickleDB 与 Rocket/Juniper 上下文一起使用？答案

【问题标题】：How do I use PickleDB with Rocket/Juniper Context?如何将 PickleDB 与 Rocket/Juniper 上下文一起使用？
【发布时间】：2020-05-25 01:14:44
【问题描述】：

我正在尝试使用 PickleDB 编写一个基于 Rocket / Juniper / Rust 的 GraphQL 服务器 - 一个内存键/值存储。

pickle db 在开始时创建/加载并交给rocket进行管理：

fn rocket() -> Rocket {
    let pickle_path = var_os(String::from("PICKLE_PATH")).unwrap_or(OsString::from("pickle.db"));
    let pickle_db_dump_policy = PickleDbDumpPolicy::PeriodicDump(Duration::from_secs(120));
    let pickle_serialization_method = SerializationMethod::Bin;

    let pickle_db: PickleDb = match Path::new(&pickle_path).exists() {
        false => PickleDb::new(pickle_path, pickle_db_dump_policy, pickle_serialization_method),
        true => PickleDb::load(pickle_path, pickle_db_dump_policy, pickle_serialization_method).unwrap(),
    };

    rocket::ignite()
        .manage(Schema::new(Query, Mutation))
        .manage(pickle_db)
        .mount(
            "/",
            routes![graphiql, get_graphql_handler, post_graphql_handler],
        )
}

我想从我的 Guard 中的 Rocket State 中检索 PickleDb 实例：

pub struct Context {
    pickle_db: PickleDb,
}

impl juniper::Context for Context {}

impl<'a, 'r> FromRequest<'a, 'r> for Context {
    type Error = ();

    fn from_request(_request: &'a Request<'r>) -> request::Outcome<Context, ()> {
        let pickle_db = _request.guard::<State<PickleDb>>()?.inner();
        Outcome::Success(Context { pickle_db })
    }
}

这不起作用，因为国家只给了我一个参考：

26 |         Outcome::Success(Context { pickle_db })
   |                                    ^^^^^^^^^ expected struct `pickledb::pickledb::PickleDb`, found `&pickledb::pickledb::PickleDb`

当我更改我的 Context 结构以包含一个引用时，我遇到了我还不熟悉的终身问题：

15 |     pickle_db: &PickleDb,
   |                ^ expected named lifetime parameter

我尝试使用 'static 确实让 rust 很不高兴，我尝试使用 FromRequest 的请求生命周期 (?) 'r，但这也不起作用...

如何让它工作？由于我对生锈很陌生，这是做事的正确方法吗？

【问题讨论】：

标签： rust rust-rocket

【解决方案1】：

我终于有了一个解决方案，尽管对 unsafe 的需求表明它不是最理想的 :)

#![allow(unsafe_code)]
use pickledb::{PickleDb, PickleDbDumpPolicy, SerializationMethod};
use serde::de::DeserializeOwned;
use serde::Serialize;
use std::env;
use std::path::Path;
use std::time::Duration;

pub static mut PICKLE_DB: Option<PickleDb> = None;

pub fn cache_init() {
    let pickle_path = env::var(String::from("PICKLE_PATH")).unwrap_or(String::from("pickle.db"));
    let pickle_db_dump_policy = PickleDbDumpPolicy::PeriodicDump(Duration::from_secs(120));
    let pickle_serialization_method = SerializationMethod::Json;
    let pickle_db = match Path::new(&pickle_path).exists() {
        false => PickleDb::new(
            pickle_path,
            pickle_db_dump_policy,
            pickle_serialization_method,
        ),
        true => PickleDb::load(
            pickle_path,
            pickle_db_dump_policy,
            pickle_serialization_method,
        )
        .unwrap(),
    };
    unsafe {
        PICKLE_DB = Some(pickle_db);
    }
}

pub fn cache_get<V>(key: &str) -> Option<V>
where
    V: DeserializeOwned + std::fmt::Debug,
{
    unsafe {
        let pickle_db = PICKLE_DB
            .as_ref()
            .expect("cache uninitialized - call cache_init()");
        pickle_db.get::<V>(key)
    }
}

pub fn cache_set<V>(key: &str, value: &V) -> Result<(), pickledb::error::Error>
where
    V: Serialize,
{
    unsafe {
        let pickle_db = PICKLE_DB
            .as_mut()
            .expect("cache uninitialized - call cache_init()");
        pickle_db.set::<V>(key, value)?;
        Ok(())
    }
}

这可以按预期简单地导入和使用，但我想当负载变高时我会遇到问题......

【讨论】：