Node.js chaining promises in a loop with MySQL - mysql

Question

I am trying to make a non-relational DB into a relational DB. So I am starting from data with no unique IDs.
I need to get the result from one SQL call loop through those rows, and for each one, do a SQL SELECT using part of the first result, then another SQL select using the next result, and then a write using IDs from the first and last queries.
I am using Node.js and ES6 promises to keep everything in order, but I seem to be missing something. I was actually trying to do an extra SQL call, and also use that result in the third query, but I am simplifying it to just get one call to feed into another.
Maybe some code will help show what I am trying to do.
Here is my query class that returns promises:
var mysql = require('mysql');
class Database {
constructor() {
this.connection = mysql.createConnection({
host: "localhost",
user: "root",
password: "root",
database: "pressfile"
});
}
query(sql, args) {
return new Promise((resolve, reject) => {
this.connection.query(sql, args, (err, result, fields) => {
if (err) return reject(err);
resolve (result);
});
});
}
close() {
return new Promise((resolve, reject) => {
this.connection.end(err => {
if (err) return reject (err);
resolve();
});
});
}
}
This was stolen pretty much as is from a tutorial site, and this part seems to work pretty well. Then here comes the loop, and the multiple queries:
var contactId;
var address1;
var orgName;
var database = new Database();
database.query("SELECT * FROM contact")
.then( result => {
for (var i = 0; i < result.length; i++) {
contactId = result[i].contactId;
orgName = result[i].org;
var sql2 = "SELECT * FROM organization WHERE (name = \"" + orgName + "\")";
console.log(sql2);
database.query(sql2)
.then(result2 => {
console.log(result2);
var orgId = result2[0].organizationId;
var sql3 = "INSERT INTO contact_organization (contactId, organizationId) VALUES (" + contactId + ", " + orgId + ")";
console.log(sql3);
return ""; //database.query(sql3);
}).then( result3 => {
console.log(result3);
});
}
}).catch((err) => {
console.log(err);
databse.close();
});
I know it is kind of unraveling at the end, but I'm not wanting to do the INSERT query until I know I can get it right. Right now in the console, I get a valid organization object, followed by:
`INSERT INTO contact_organization (contactId, organizationId) VALUES (17848, 29)'
17848 is the final contactId that is returned in the for loop. How can I get the contactId that is assigned before the second query. I know I am not doing this asynchronous stuff right.

Answer 1

Try something like this. Just a quick solution. (not tested).
const selectOrg = (result) => {
contactId = result[i].contactId;
orgName = result[i].org;
var sql = "SELECT * FROM organization WHERE (name = \"" + orgName + "\")";
return database.query(sql);
};
const insertOrg = (result) => {
var orgId = result[0].organizationId;
var sql = "INSERT INTO contact_organization (contactId, organizationId) VALUES (" + contactId + ", " + orgId + ")";
return database.query(sql);
};
database.query("SELECT * FROM contact")
.then(result => {
const promises = [];
for (var i = 0; i < result.length; i++) {
promises << selectOrg(result)
.then(insertOrg);
}
return Promise.all(promises);
})
.then(allResults => {
console.log(allResults);
})
.catch((err) => {
databse.close();
});

Answer 2

I found a way to do this, but it is kind of cheesy. I included the contactId as a constant in the SQL query to get the organization, so I could then pass the value to the .then, keeping everything in order.
My sql2 statement becomes:
var sql2 = "SELECT *, " + contactId + " AS contactId FROM organization WHERE (name = \"" + orgName + "\")";
Then when that query returns, I can just pull the correct contactId out as result[0].contactId, from the same result I get the organizationId from.
Here is the final code:
database.query("SELECT * FROM contact")
.then( result => {
for (var i = 0; i < result.length; i++) {
var contactId = result[i].contactId;
var orgName = result[i].org;
var sql2 = "SELECT *, " + contactId + " AS contactId FROM organization WHERE (name = \"" + orgName + "\")";
database.query(sql2)
.then(result2 => {
var orgId = result2[0].organizationId;
var contactId = result2[0].contactId;
var sql3 = "INSERT INTO contact_organization (contactId, organizationId) VALUES (" + contactId + ", " + orgId + ")";
console.log(sql3);
return database.query(sql3);
}).then( result3 => {
console.log(result3);
});
}
}).catch((err) => {
console.log(err);
databse.close();
});
The console.log(result3) returns a bunch of these:
OkPacket {
fieldCount: 0,
affectedRows: 1,
insertId: 0,
serverStatus: 2,
warningCount: 0,
message: '',
protocol41: true,
changedRows: 0 }
And I got one contact_organization inserted for every contact row returned from the first query.