Loop through Array and perform My SQL query based on result of previous query for each entry in the array

Question

I have an array of items:

var myArr = ['item1', 'item2', 'item3'];

I'm attempting to loop over these items and check if they exist in my database. If the item does not exist, then I add it to the database.

var sql = 'Select * from DB where item="' + myArr[i] + '"';
connection.query(sql, function(e, r, f) {
    if(!e && r.length <= 0) {
        performInsertOnDB(myArr[i]);
    }
});

My trouble is, the reference to variable i will not stay as connnection.query is asynchronous. I need to wait until the first select finishes before I can continue. I'm trying to use the Async library to accomplish this, but I must not be fully grasping how to perform the task.

This is what I have so far:

async.each(lootArray, function(lootItem, addLootItem) {
    var sql = "SELECT * FROM loot_history WHERE date = DATE('" + moment(lootItem[1]).format('YYYY-MM-DD') + "') AND time = '" + lootItem[2] + "' AND itemId = " + lootItem[4];
    connection.query(sql, function(error, results, fields) {
        if (error) {
            sendDiscordMessage(loachannel, error + ', <@105094681141977088>');
            return false;
        } else {
            if (results.length > 0) {
                //duplicates.push(lootArray[i]);
            } else {
                addLootItem(lootItem);
            }
        }
    });
}, function(err) {
    // if any of the file processing produced an error, err would equal that error
    if (err) {
        // One of the iterations produced an error.
        // All processing will now stop.
        console.log('A file failed to process');
    } else {
        console.log('All files have been processed successfully');
    }
});

function addLootItem(lootItem) {
    var sql = "INSERT INTO loot_history SET player = " + lootItem[0] + ", date = " + moment(lootItem[1]).format('YYYY-MM-DD') + ", time = '" + lootItem[2] + ", item = " + lootItem[3] + ", itemId = " + lootItem[4] + ", itemString=" + lootItem[5] + ", response= " + lootItem[6] + ", votes= " + lootItem[7] + ", class= " + lootItem[8] + ", instance=" + lootItem[9] + ", boss=" + lootItem[10] + ", gear1=" + lootItem[11] + ", gear2=" + lootItem[12] + ", reasponseId=" + lootItem[13] + ", isAwardReason=" + lootItem[14];
    connection.query(sql, function(error, results, fields) {
        if (error) {
            sendDiscordMessage(loachannel, error + ', <@105094681141977088>');
        }
    });
}

EDIT: Everything works, except the callback AddLootItem is not firing. Why is this callback not getting called? I can set log events in that if statement that execute, but the function itself never fires.

Lena Kaplan · Accepted Answer · 2017-07-03 18:01:20Z

The problem is that the name of async callback is the same as the function you want to be called when the item does not exist. Try to change the name in the function to something else let's say: callback, and call it in your if statement or pass it to addLootItem, and call it there once the item added.

async.each(lootArray, function(lootItem, callback) {
    var sql = "SELECT * FROM loot_history WHERE date = DATE('" + moment(lootItem[1]).format('YYYY-MM-DD') + "') AND time = '" + lootItem[2] + "' AND itemId = " + lootItem[4];
    connection.query(sql, function(error, results, fields) {
        if (error) {
            sendDiscordMessage(loachannel, error + ', <@105094681141977088>');
            calback(err);
        } else {
            if (results.length > 0) {
                //duplicates.push(lootArray[i]);
                callback();
            } else {
                addLootItem(lootItem, callback);
            }
        }
    });
}, function(err) {
    // if any of the file processing produced an error, err would equal that error
    if (err) {
        // One of the iterations produced an error.
        // All processing will now stop.
        console.log('A file failed to process');
    } else {
        console.log('All files have been processed successfully');
    }
});

function addLootItem(lootItem, done) {
    var sql = "INSERT INTO loot_history SET player = " + lootItem[0] + ", date = " + moment(lootItem[1]).format('YYYY-MM-DD') + ", time = '" + lootItem[2] + ", item = " + lootItem[3] + ", itemId = " + lootItem[4] + ", itemString=" + lootItem[5] + ", response= " + lootItem[6] + ", votes= " + lootItem[7] + ", class= " + lootItem[8] + ", instance=" + lootItem[9] + ", boss=" + lootItem[10] + ", gear1=" + lootItem[11] + ", gear2=" + lootItem[12] + ", reasponseId=" + lootItem[13] + ", isAwardReason=" + lootItem[14];
    connection.query(sql, function(error, results, fields) {
        if (error) {
            sendDiscordMessage(loachannel, error + ', <@105094681141977088>');
        }
        done();
    });
}

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