我们如何在 rusqlite 中使用带有外部 WHERE 参数的 SELECT 查询？

问题描述

我需要使用 SELECT 和 WHERE 从数据库中获取一行，我需要根据年龄获取一行，我使用其他教程尝试过这种方式。

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

#[derive(Debug)]
struct Person {
    id: i32,name: String,age: u8,data: String,}

fn main() -> Result<()> {
    let conn = Connection::open_in_memory()?;

    conn.execute(
        "CREATE TABLE person (
                  id              INTEGER PRIMARY KEY,name            TEXT NOT NULL,age           INTEGER,data            TEXT
                  )",[],)?;
    let me = Person {
        id: 0,name: "Steven".to_string(),age:1,data: "data1".to_string(),};
    conn.execute(
        "INSERT INTO person (name,age,data) VALUES (?1,?2,?3)",params![me.name,me.age,me.data],)?;

    conn.execute(
        "INSERT INTO person (name,params!["john".to_string(),2,"data2".to_string()],)?;
    
    let age:u8 = 1;
    
    let mut stmt = conn.prepare("SELECT id,name,data FROM person WHERE age=:age;")?;
    let person_iter = stmt.query_map([],|row| {
        Ok(Person {
            id: row.get(0)?,name: row.get(1)?,age: row.get(2)?,data: row.get(3)?,})
    })?;

    for person in person_iter {
        println!("Found person {:?}",person);
    }

    Ok(())
}

我们如何使用带有外部 WHERE 参数的 SELECT 查询？

解决方法

您可以像这样使用 params 的 query_map()：

stmt.query_map(&[(":age",age.to_string().as_str())],|row| { ... }

基于您在问题中的代码的完整工作示例：

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

#[derive(Debug)]
struct Person {
    id: i32,name: String,age: u8,data: String,}

fn main() -> Result<()> {
    let conn = Connection::open_in_memory()?;

    conn.execute(
        "CREATE TABLE person (
                  id              INTEGER PRIMARY KEY,name            TEXT NOT NULL,age           INTEGER,data            TEXT
                  )",[],)?;
    let me = Person {
        id: 0,name: "Steven".to_string(),age:1,data: "data1".to_string(),};
    conn.execute(
        "INSERT INTO person (name,age,data) VALUES (?1,?2,?3)",params![me.name,me.age,me.data],)?;

    conn.execute(
        "INSERT INTO person (name,params!["john".to_string(),2,"data2".to_string()],)?;
    
    let age:u8 = 1;
    
    let mut stmt = conn.prepare("SELECT id,name,data FROM person WHERE age=:age;")?;
    let person_iter = stmt.query_map(&[(":age",|row| {
        Ok(Person {
            id: row.get(0)?,name: row.get(1)?,age: row.get(2)?,data: row.get(3)?,})
    })?;

    for person in person_iter {
        println!("Found person {:?}",person);
    }

    Ok(())
}

rusqlite rust