Using knex.js updates existing column with results of select query - mysql

Question

Product (id, currentdraw, totaldraw, ratio)
Product is my table
I want to use currentdraw and totaldraw to update ratio
Here is my code
Product.updateRatio = function(pid, cb) {
db('product')
.where({
productid : pid
})
.select('currentdraw', 'totaldraw')
.then(function(ratiolist) {
db('product')
.where({
productid : pid
})
.update({
ratio : ratiolist.currentdraw / ratiolist.totaldraw
})
cb(null, ratiolist);
})
.catch(function(err) {
cb(new GeneralErrors.Database());
console.log('updateRatio');
});
}
When I run the code, no error occuring but ratio column doesn't update.
I don't know where is wrong.
Can someone help me? Thanks

Answer 1

I suppose that your ratiolist is array instead of an object, add console.dir(ratiolist) to check what is returned from the first query:
function(ratiolist) {
// here ratiolist is an array
db('product')
.where({
productid : pid
})
.update({
// undefined / undefined is NaN
ratio : ratiolist.currentdraw / ratiolist.totaldraw
})
// second query is not yet ran when this callback is called
// try to use promise chains...
cb(null, ratiolist);
})
Better way to do this query would be:
// return value passed as promise instead of callback
Product.updateRatio = function(pid) {
return db('product')
.where('productid', pid)
.update({
ratio : db.raw('?? / ??', ['currentdraw', 'totaldraw'])
})
.then(() => db('product').where('productid', pid));
}
If you insist using callbacks this should work:
Product.updateRatio = function(pid, cb) {
db('product')
.where('productid', pid)
.update({
ratio : db.raw('?? / ??', ['currentdraw', 'totaldraw'])
})
.then(() => db('product').where('productid', pid))
.then(ratiolist => cb(null, ratiolist));
}