Unable to assign a value in a javascript function while fetching from sqlite [duplicate]

Question

Unable to assign a value in a javascript function while fetching from sqlite.

For Eg: This code in not working

function bookContent(dtb) {

    var bkContent = '';     

    dtb.all("SELECT count(*) ttlRw FROM books;", function(err, row) {

        if (err)
        bkContent = "Error SQL";
        else
        {           

            if(parseInt(row[0].ttlRw)>0)
            {
                bkContent = row[0].ttlRw + " rows";
            }
            else
            bkContent = 'No rows found!';                   
        }

    });

    return bkContent;

}

It's returns an empty value.

This is working

function bookContent(dtb) {

    dtb.all("SELECT count(*) ttlRw FROM books;", function(err, row) {

        if (err)
        document.getElementById("bookCnt").innerHTML = "Error SQL";
        else
        {           

            if(parseInt(row[0].ttlRw)>0)
            {
                document.getElementById("bookCnt").innerHTML = row[0].ttlRw + " rows";
            }
            else
            document.getElementById("bookCnt").innerHTML = 'No rows found!';                    
        }

    });

}

I want the first one work. Please tell me, where i am wrong.

forrestmid · Accepted Answer · 2017-02-04 17:38:59Z

1

You're returning a value before the asynchronous dtb.all() finishes. You need to pass a callback to bookContent and call it when the database query finishes.

var globalBkContent = "";  
function bookContent(dtb, callback) {
    dtb.all("SELECT count(*) ttlRw FROM books;", function(err, row) {

        if (err)
        return callback("Error SQL");
        else
        {           

            if(parseInt(row[0].ttlRw)>0)
            {
                return callback(false, row[0].ttlRw + " rows");
            }
            else
            return callback("No rows found!")           
        }

    });
}

var dtb = new DatabaseInstance();//Or whatever your dtb variable is defined as.
bookContent(dtb, function(err, bkContent) {
    if(err) throw(err);
    globalBkContent = bkContent;
    console.log(bkContent); //Here your bkContent & globalBkContent are both accessible and have the correct values. 
    //Make sure you don't do anything with globalBkContent until it is set by this function.
})

//If I access globalBkContent outside the callback above then it will still be an empty string.

edited Feb 4, 2017 at 17:38

answered Feb 4, 2017 at 0:58

forrestmid

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10 Comments

Jay Over a year ago

Thanks @forrestmid for your reply. But still how can i get the bkContent value outside bookContent(); Like assign to a global variable.

forrestmid Over a year ago

@Jay Your question doesn't ask anything about a global variable. I'll modify my answer to allow for a global variable, but your primary issue is because you're returning the function before the asynchronous portion has finished.

forrestmid Over a year ago

@Jay Additionally, you can't do anything with bkContent until your callback is returned, simply because it hasn't been set yet. You need to read up on how asynchronous functions work in Node if you want to be able to program in it. It's vitally necessary to know how to nest asynchronous functions in order to accomplish a goal in the programming language.

Jay Over a year ago

Thanks @forrestmind. Thanks for the help.

Jay Over a year ago

SORRY! It's not working

|

Teymur Mardali · Accepted Answer · 2017-02-03 22:15:32Z

0

I have basic knowledges Nodejs, but I think it returns empty value because in the first code your return bkContent out of the dtb.all() function. But in the second code, you write in the function.

answered Feb 3, 2017 at 22:15

Teymur Mardali

8477 silver badges20 bronze badges

4 Comments

Jay Over a year ago

Thanks @Teymur Mardaliyer Lennon for your reply. I tried it inside the dtb.all. But then the function returns an 'undefined' msg;

Teymur Mardali Over a year ago

@Jay may be it will help you? stackoverflow.com/questions/25399725/… or stackoverflow.com/questions/18361930/… or you need just return value?

Teymur Mardali Over a year ago

Also you can test seems like this

var result = dtb.all("SELECT count(*) ttlRw FROM books;", function(err, row) {...... return bkContent; }); console.log(result);

hm?

Jay Over a year ago

i tried it. but it's returns a DB object. Not the values returns from bkContent. I will try the links you specified above. Thanks once again for the help.

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