NodeJS - unable to create a recursive MySQL request properly

Question

I have a table called categories which should hold the categories of articles available on my site. I want to have a parent and child system in the table, where a category with no parent has the value of 0 for its parent column. A category that has a parent will hold the id of its parent category in its parent column.

To query it I have created this function:

function categoryTree(table, parent = 0) {
    var categTreeArr = [];
    return new Promise(resolve => {
        dbCon.promise().execute("select * from " + table + " where parent = " + parent, []).then(function (err, result, fields) {
            result.forEach(e => {
                var categTreeArrNext = categoryTree(table, e.id).then((value) => {
                    categTreeArr.push([e.img, e.name, e.slug, value]);
                });
            });
            resolve(categTreeArr);
        })
    })
}

On my index page, I have used this code to call the function:

categArr = myModule.categoryTree("course_category", 0).then(value => {
            setValue(row, response, value)
            console.log(value)
});

This gives me an UnhandledPromiseRejectionWarning. Please Help.

PS: I am new to NodeJS. If anything about this question is wrong, please don't flag it. If the question is unclear, I will clarify it in the comment.

José Henrique · Accepted Answer · 2021-12-14 16:55:12Z

1

Appearenly, your promise is being rejected and there's not a catch block to handle it. Try catching the whole function and see what is actually going on.

categArr = myModule.categoryTree("course_category", 0).then(value => {
            setValue(row, response, value)
            console.log(value)
}).catch(e => console.log(e));

answered Dec 14, 2021 at 16:55

José Henrique

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1 Comment

Yash Kejriwal Over a year ago

I found the other way round - instead of creating a function that queries the database and sorts the result accordingly, I called the mysql2 query inside of the index page and then passing it to a function that sorts it in the form of a parent-child tree. This way I can keep the code simpler and avoid errors. Thanks for the reply though - it will be helpful in the future :)

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