为什么Rusqlite在执行查询时拒绝Option类型？

Question

我正在尝试将CSV数据插入到SQLite数据库中。stripe_id是可选的，因此它的类型是Option<&str>。所有其他字段均为&str。当我使用conn.execute插入值时，它们都正确插入，除了stripe_id，它抛出一个错误，说明它需要&str而不是Option。

我搜索了文档和Option<T>实现了ToSQL，当我尝试用包含Option值的Rusqlite示例替换我的代码时，它对示例代码抛出了相同的错误。

相关的结构和查询代码片段：

struct Merchant<'a> {
    name: &'a str,
    billing_portal: &'a str,
    billing_period: &'a str,
    stripe_id: Option<&'a str>,
}

conn.execute(
    "INSERT INTO merchants (name, billing_portal, billing_period, stripe_id)
     values (?, ?, ?, ?)",
     &[&merch.name, &merch.billing_portal, &merch.billing_period, &merch.stripe_id]
).expect("Error inserting merchant into database");

错误：

error[E0308]: mismatched types
  --> src/main.rs:38:75
   |
38 |              &[&merch.name, &merch.billing_portal, &merch.billing_period, &merch.stripe_id]
   |                                                                           ^^^^^^^^^^^^^^^^ expected `&str`, found enum `std::option::Option`
   |
   = note: expected reference `&&str`
              found reference `&std::option::Option<&str>`

以及完整的代码：

extern crate csv;
extern crate rusqlite;

use rusqlite::{Connection, Result};

#[derive(Debug)]
struct Merchant<'a> {
    name: &'a str,
    billing_portal: &'a str,
    billing_period: &'a str,
    stripe_id: Option<&'a str>,
}

fn main() -> Result<()> {
    let conn = Connection::open("data.sqlite")?;

    let mut reader = csv::ReaderBuilder::new()
                                        .has_headers(false)
                                        .from_path("merchants.csv")
                                        .expect("Failed to read csv");
    for record in reader.records() {
        let record = record.unwrap();
        let merch = Merchant {
            name: &record[0],
            billing_portal: &record[3],
            billing_period: &record[4],
            stripe_id: (match &record[5] {
                x if x == "" => None,
                x            => Some(x)
            }),
        };
        println!("{:?}", &merch);

        conn.execute(
            "INSERT INTO merchants (name, billing_portal, billing_period, stripe_id)
             values (?, ?, ?, ?)",
             &[&merch.name, &merch.billing_portal, &merch.billing_period, &merch.stripe_id]
        ).expect("Error inserting merchant into database");

    }

    Ok(())
}

Answer 1

使用rusqlite::params宏可解决此问题：

use rusqlite::{params, Connection, Result};

fn main() -> Result<()> {
    // ...

    for record in reader.records() {
        // ...

        conn.execute(
            "INSERT INTO merchants (name, billing_portal, billing_period, stripe_id)
             values (?, ?, ?, ?)",
            params![
                &merch.name,
                &merch.billing_portal,
                &merch.billing_period,
                &merch.stripe_id,
            ],
        )
        .expect("Error inserting merchant into database");
    }

    Ok(())
}