In general how does javascript interpret a Database {} object? I am writing some back end scripts to handle a registration form verification. In particular I need to ensure that the username and email used to register is not currently in use. To do this I use the sqlite3 package and use a few db.get calls to determine if there are existing entries in my database for the username and email used on the registration form. I want to use the return of db.get to check if it is empty or not and use this conditional to perform the necessary task. However the db.get returns a Database {} object which I am unfamiliar of how to work with.
Hopefully the following pseudo describes the issue better. Here uname returns Database {} and so never fails the if statement.
function existance(username, email) {
let uname = db.get(sql, username, callback(err, throw));
if (uname) {
let errors = {username: 'Username already in use.'};
return errors;
}
};
EDIT
I have since used Gajiu's recommendation but still having issues. So I have two files:
registrant_existence.js
// necessary requirements and initialisation
function registrant_existence(username) {
let uname;
let sql = 'SELECT username FROM table WHERE username=?';
db.get(sql, username, function(err, row) {
if (err) {
throw err;
} else {
uname = row;
console.log(uname);
}
});
console.log(uname);
if (uname !== undefined) {
return {username: 'Username already in use.'};
} else {
return 'DNE';
}
};
module.exports = registrant_existence;
register.js
let registrant_existence = require("path to registrant_existence.js");
// necessary requirements and initialisation
router.post('/', function(req, res) {
let existence = registrant_existence(req.body.username, req.body.email);
if (existence != 'DNE') {
// render registration page notifying the user
// that the username is already in use
} else {
// register the new user details
}
});
The uname variable is undefined always. I placed the console.log(uname) in two spots in registrant_existence.js as is seen above to see what is happening. Two strange things occur.
The first is that the console.log(uname) outside the db.get() displays undefined in the console and the console.log(uname) inside the db.get() displays the expected string (a username I know is in my database).
The second is that the console.log(uname) outside the db.get() is displayed before the console.log(uname) _inside the db.get() in my console.
I have no idea why these things are happening. Does anyone have any suggestions?
You should try something like that:
db.get(sql, username, (err, data) => {
// process the data here
if (err) {
return console.error(err.message);
}
return data
? console.log(data.id, data.userName)
: console.log('No username found');
});
I guess you are looking for a wrapper around your Database object, something like an Object Relational Mapper (ORM), this one is used regularly https://sequelize.org/master/manual/getting-started.html
On the other hand for your specific use case you might want to get a look at this https://www.sqlite.org/lang_createtable.html#unique_constraints: unicity is usually via constraints in the data store.
Related
So basically I have a similar block written in Express:
var sqlite3 = require('sqlite3');
const data = {};
const db = new sqlite3.Database("sqlite/test.db");
db.run("INSERT INTO [Employees]([Name]) VALUES(?)", [name], function (err) {
if (err) { //this is the error block
data.error = err.code;
data.status = 0;
}
else { //this is the success block
data.data = { Name: name, Id: this.lastID };
data.status = 1;
}
db.close();
res.send(data);
});
This does what it looks like, just a simple insert statement and its callback. The update, select and delete operations are literally all the same.
But whenever I get errors (syntax error, missing fields, missing tables, yada yada), I always just get {errNo: 0, code: "SQLITE_ERROR"} in my err argument, which is annoyingly unspecific and unhelpful.
Is there a way to fix the error handling and make it not insanity inducing?
This is the closest thing I found to documentation on the error object. You probably want to look at err.message.
I tried to create function that get the admin rows from users table mysql. Then I want to store it to the variable to check it latter, but when I console log it, it just return undifined. I knows this about async and should using callbacks or promises. But I'm really new about this, please help!
exports.admin = function(req, res) {
var isAdmin = connection.query('SELECT admin FROM users where first_name = "yehezkiel"',function(error,rows,fields){
if(error){
console.log(error)
} else{
return rows[0].admin // returning 1
}
});
console.log(isAdmin.values) //return undifined
};
I have code that attempts to access a database and search it for a specific field. The database itself is not exactly accessible by me; I can only pull certain information from it. In the following code, when the field exists, the code returns the respective user info. When it does not exist, it skips the code and returns absolutely nothing. How can I make my code know that the code was skipped and it isn't just a latency compensation problem. I was trying to make the code return null or undefined and then check for that in a variable, but I'm not sure how to do that. This code is on the server side:
client.search(base, options, function (err, res) {
if (err) {
console.log('search error:' + err);
}
res.on('searchEntry', function (entry) {
if (JSON.stringify(entry.object, null, 2) === undefined) {
userData = null;
}
else {
userData = JSON.stringify(entry.object, null, 2);
}
});
});
I would like to 'functionalize' my queries by putting them into functions which have apt names for the task.
I want to avoid putting everything in the req, res functions (my controllers), and instead put them in 'models' of sorts, that is, another JavaScript file that will be imported and used to run the functions that execute queries and return the results on behalf of the controller.
Assuming that I have the following setup for the queries:
UserController.js
exports.userAccount = function(req, res, next) {
var queryText = "\
SELECT *\
FROM users\
WHERE id = $1\
";
var queryValues = [168];
pg.connect(secrets.DATABASE_URL, function(err, client, done) {
client.query(queryText, queryValues, function(err, result) {
res.render('pathToSome/page', {
queryResult: result.rows
});
});
});
}
Here, while I'm in the query, I essentially redirect and render a page with the data. That works fine. But I want to take out all that pg.connect and client.query code and move it to a separate file to be imported as a model. I've come up with the following:
UserModel.js
exports.findUser = function(id) {
// The user to be returned from the query
// Local scope to 'findUser' function?
var user = {};
var queryText = "\
SELECT *\
FROM users\
WHERE id = $1\
";
var queryValues = [id];
pg.connect(secrets.DATABASE_URL, function(err, client, done) {
client.query(queryText, queryValues, function(err, result) {
// There is only ever 1 row returned, so get the first one in the array
// Apparently this is local scope to 'client.query'?
// I want this to overwrite the user variable declared at the top of the function
user = result.rows;
// Console output correct; I have my one user
console.log("User data: " + JSON.stringify(user));
});
});
// I expect this to be correct. User is empty, because it was not really
// assigned in the user = result.rows call above.
console.log("User outside of 'pg.connect': " + JSON.stringify(user));
// I would like to return the user here, but it's empty!
return user;
};
and I'm calling my model function as so:
var user = UserModel.findUser(req.user.id);
The query executes perfectly fine in this fashion - except that the user object is not being assigned correctly (I'm assuming a scope issue), and I can't figure it out.
The goal is to be able to call a function (like the one above) from the controller, have the model execute the query and return the result to the controller.
Am I missing something blatantly obvious here?
pgconnect is an asynchronous call. Instead of waiting for data to return from the database before proceeding with the next line, it goes ahead with the rest of the program before Postgres answers. So in the code above, findUser returns a variable that has not yet been populated.
In order to make it work correctly, you have to add a callback to the findUser function. (I told you wrong in a previous edit: The done parameter in pg.connect is called in order to release the connection back to the connection pool.) The final result should look something like this:
exports.findUser = function(id, callback) {
var user = {};
var queryText = "SELECT FROM users WHERE id = $1";
var queryValues = [id];
pg.connect(secrets.DATABASE_URL, function(err, client, done) {
client.query(queryText, queryValues, function(err, result) {
user = result.rows;
done(); // Releases the connection back to the connection pool
callback(err, user);
});
});
return user;
};
And you'd use it, not like this:
var user = myModule.findUser(id);
But like this:
myModule.findUser(id, function(err, user){
// do something with the user.
});
If you have several steps to perform, each of them dependent on data from a previous asynchronous call, you'll wind up with confusing, Inception-style nested callbacks. Several asynchronous libraries exist to help you with making such code more readable, but the most popular is npm's async module.
I'm new to mongoose/mongodb and I am trying to do some sort of error handling with my document save.
I am trying to create a stub id to store into the db for easier data retrieval later on (and also to put into the url bar so people can send links to my website to that particular page more easily -- like jsfiddle or codepen).
Basically I want to search for a document with a page_id and if it exists, I want to regenerate that page_id and search until it gets to one that's unused like this:
while(!done){
Model.findOne({'page_id': some_hex}, function (err, doc) {
if(doc){
some_hex = generate_hex();
}
else
{
done = true;
}
});
}
model.page_id = some_hex;
model.save();
However, since mongoose is asynchronous, the while loop will pretty much run indefinitely while the find works in the background until it finds something. This will kill the resources on the server.
I'm looking for an efficient way to retry save() when it fails (with a change to page_id). Or to try and find an unused page_id. I have page_id marked as unique:true in my schema.
Retrying should be performed asynchronously:
var tryToSave = function(doc, callback) {
var instance = new Model(doc);
instance.page_id = generate_hex();
instance.save(function(err) {
if (err)
if (err.code === 11000) { // 'duplicate key error'
// retry
return tryToSave(doc, callback);
} else {
// another error
return callback(err);
}
}
// it worked!
callback(null, instance);
});
};
// And somewhere else:
tryToSave(doc, function(err, instance) {
if (err) ...; // handle errors
...
});