sqlite.get() 导致 TypeError:无法读取 null 的属性“get" [英] sqlite.get() results in TypeError: Cannot read property 'get' of null

问题描述

当尝试执行 sql.get() 调用时，它在某些地方有效，但在其他地方无效，我似乎无法弄清楚有什么区别.
数据库已成功打开，或者至少我从未收到错误并且从未关闭过.我还在第二个(工作示例)中使用了 Discord.js，但不确定这是否相关.
在这个例子中它不起作用.
测试.js:

When trying to execute a sql.get() call it works in some places, but not in others and I can't seem to figure out what's the difference.
The database is sucessfully opened or at least I never got an error and it never gets closed. I also use Discord.js in the second (working example), not sure if that is relevant, though.
In this example it doesn't work.
test.js:

const sql = require("sqlite");
sql.open("./data.sqlite");

exports.getItemID = function(item) {
    return new Promise(function (fulfill, reject){
        sql.get(`SELECT * FROM items WHERE name="${item}"`).then(row => {
            console.log(`do stuff`);
        }).catch((e) => {
            console.error;
            reject(e);
        })
    });
}

exports.getItemID("Coins").then(itemID => {
    console.log(itemID);
}).catch((e) => {
    console.log(e);
});

堆栈跟踪:

$ node test.js 
TypeError: Cannot read property 'get' of null
    at Promise (/Users/julianveerkamp/node_modules/sqlite/main.js:225:18)
    at Promise (<anonymous>)
    at Database.get (/Users/julianveerkamp/node_modules/sqlite/main.js:224:12)
    at /Users/julianveerkamp/workspace/test-bot/test.js:6:13
    at Promise (<anonymous>)
    at Object.exports.getItemID (/Users/julianveerkamp/workspace/test-bot/test.js:5:12)
    at Object.<anonymous> (/Users/julianveerkamp/workspace/test-bot/test.js:15:9)
    at Module._compile (module.js:573:30)
    at Object.Module._extensions..js (module.js:584:10)
    at Module.load (module.js:507:32)

但是当我用

const sql = require("sqlite");
sql.open("./data.sqlite");
// other stuff
let commandFile = require(`./commands/command.js`);
commandFile.run(client, message, args);
// other stuff

它工作得很好.

command.js:

command.js:

const sql = require("sqlite");
sql.open("./data.sqlite");

exports.run = (client, message, args) => {
    sql.get(`SELECT * FROM scores WHERE userID ="${message.author.id}"`).then(row => {
        // Do stuff with row
    }).catch(() => {
        console.error;
    });
}

推荐答案

这可能是 sqlite 中的一个错误，所以我继续使用 sqlite3 代替并包装/promisified自己使用 util.promisify() 函数.

This might be a bug in sqlite so I went ahead and used sqlite3 instead and wrapped/promisified the functions myself with util.promisify().

const util = require('util');
const sqlite3 = require('sqlite3');

var db = new sqlite3.Database('./data.sqlite');

db.get = util.promisify(db.get);
db.run = util.promisify(db.run);

exports.getItemID = function(item) {
    return new Promise(function (fulfill, reject){
        db.get(`SELECT * FROM items WHERE name="${item}"`).then(row => {
            console.log(`do stuff`);
        }).catch((e) => {
            console.error;
            reject(e);
        });
    });
}

exports.getItemID("Coins").then(itemID => {
    console.log(itemID);
}).catch((e) => {
    console.log(e);
});

注意:函数内部的新 Promise 不是必须的.人们可以从 get 函数返回承诺.

Note: The new Promise inside the function is not necessary. One could just return the promise from the get function.

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