CODEWITHSUNDEEP
node.jspromise
Manaar
Manaar

Reputation: 212

Using promise to pass results of one NodeJS module.export function to another NodeJS module.export function

I'm working in some existing NodeJS code with Core and CoreTest as two of the functions. CoreTest runs a query and stores the selected rows in a variable called CoreSQL. Core is also running some queries, however it requires part of CoreSQL as a parameter for one of the queries.

I think I'm calling CoreTest incorrectly

module.exports = {

    CoreTest: (req, res) => {
        return new Promise((resolve, reject) => {
            const core = db.format.escape(req.query.q);
            const coreSQL = `query with parameter = ${core}`;
            returnData(coreSQL, resolve, reject);
            resolve(coreSQL);
        })
    },

    Core: (req, res) => {
        return new Promise((resolve, reject) => {
            if (req.query.q.length > 0) {
                var core = module.exports.CoreTest(req, res);
            }
            else
            {
                reject("PROBLEMS")
            }
            const coreSQLceDevID = `query where parameter like ${core}`
            const coreSQLpID = `query where parameter like ${coreSQLceDevID})`
            const coreSQL = `query where parameter like ${coreSQLpID}`
            returnDataB(coreSQL, resolve, reject);
        })
    } 
}

The return data functions run the SQL query and looks as follows:

const returnData = (sql, resolve, reject) => {
    db.query(sql, (err, result) => {
        if (err)
            reject(err)
        else
            resolve(result)
    })
}

I'm getting the following error: 

error: Unhandled rejection!
Reason:TypeError: Cannot read property 'q' of undefined,
Promise: [object Promise]

Although when I use breakpoints to check the value of q, its not undefined, so it must be an issue with how CoreTest is being called.

Upvotes: 1

Views: 156

Answers (1)

Bergi
Bergi

Reputation: 664547

Two problems:

  • in CoreTest, you are calling both returnData and resolve. Drop the immediate resolve() call, returnData will do that later. (Btw, I'd recommend renaming that to runQuery or so).

    CoreTest(req, res) {
    return new Promise((resolve, reject) => {
        const core = db.format.escape(req.query.q);
        const coreSQL = `query with parameter = ${core}`;
        returnData(coreSQL, resolve, reject);
    })
}

  • in Core, you seem to expect CoreTest() to return a value synchronously. It can't do that, it returns a promise. You will need to chain the rest of your code to that with then or await. Also you should keep the new Promise wrapper minimal:

    Core(req, res) {
    if (req.query.q.length == 0) {
        return Promise.reject("PROBLEMS");
    }
    return module.exports.CoreTest(req, res).then(core => {
//                                          ^^^^^
        return new Promise((resolve, reject) => {
            const coreSQLceDevID = `query where parameter like ${core}`
            const coreSQLpID = `query where parameter like ${coreSQLceDevID})`
            const coreSQL = `query where parameter like ${coreSQLpID}`
            returnDataB(coreSQL, resolve, reject);
        });
    });
}

Upvotes: 2

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