为什么 Rusqlite 在执行查询时拒绝 Option 类型? [英] Why does Rusqlite reject the Option type when executing a query?

问题描述

我正在尝试将 CSV 数据插入到 SQLite 数据库中.stripe_id 是可选的，所以它的类型是 Option<&str>.所有其他字段都是 &str.当我使用 conn.execute 插入值时，除了 stripe_id 之外，它们都正确插入，这会抛出一个错误，说它需要 &str而不是 Option.

I'm trying to insert CSV data into a SQLite database. stripe_id is optional, and so its type is Option<&str>. All the other fields are &str. When I use conn.execute to insert the values, they all insert correctly except for stripe_id, which throws an error saying it expects &str and not Option.

我搜索了文档并且 Option 实现了 ToSQL，当我尝试用包含 的 Rusqlite 示例替换我的代码时Option 值，它会为示例代码抛出相同的错误.

I've searched the docs and Option<T> implements ToSQL, and when I've tried replacing my code with the Rusqlite example that includes an Option value, it throws the same error for the example code.

相关的结构和查询代码片段:

The relevant struct and query code snippet:

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(())
}

推荐答案

使用 rusqlite::params 宏解决问题:

Using the rusqlite::params macro solves the problem:

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(())
}

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