Javascript – allow null value for sequelize foreignkey

javascriptnode.jspostgresqlsequelize.js

How do I allow null for a foreignkey? I have a through and belongsToMany association:

Shelf
    belongsToMany(Book, { through: Library, as: "Books"});

Book
    belongsToMany(Shelf, { through: Library, as: "Shelves"});

Library
    section: DataTypes.STRING,
    // ... other fields

I would like to record a null on the bookId in Library:

Library.create({
    section: "blah",
    bookId: null,
    shelfId: 3
});

Since Sequelize automatically creates the bookId and shelfId in the join table Library, how would I specify that I want to allow a null on the bookId foreignkey in Library?

Best Solution

I am no expert on node.js nor sequelize.js, but with one search in google I got the official documentation. You might need to pay some attention to this part of the code in the documentation:

Library.hasMany(Picture, {
  foreignKey: {
    name: 'uid',
    allowNull: false
  }
});

It seems you need to specify the {foreignKey: {name: 'bookId', allowNull: true} } in Library.

Related Solutions

Javascript – Which “href” value should I use for JavaScript links, “#” or “javascript:void(0)”

I use javascript:void(0).

Three reasons. Encouraging the use of # amongst a team of developers inevitably leads to some using the return value of the function called like this:

function doSomething() {
    //Some code
    return false;
}

But then they forget to use return doSomething() in the onclick and just use doSomething().

A second reason for avoiding # is that the final return false; will not execute if the called function throws an error. Hence the developers have to also remember to handle any error appropriately in the called function.

A third reason is that there are cases where the onclick event property is assigned dynamically. I prefer to be able to call a function or assign it dynamically without having to code the function specifically for one method of attachment or another. Hence my onclick (or on anything) in HTML markup look like this:

onclick="someFunc.call(this)"

onclick="someFunc.apply(this, arguments)"

Using javascript:void(0) avoids all of the above headaches, and I haven't found any examples of a downside.

So if you're a lone developer then you can clearly make your own choice, but if you work as a team you have to either state:

Use href="#", make sure onclick always contains return false; at the end, that any called function does not throw an error and if you attach a function dynamically to the onclick property make sure that as well as not throwing an error it returns false.

Use href="javascript:void(0)"

The second is clearly much easier to communicate.

Javascript – How to check for an empty/undefined/null string in JavaScript

If you just want to check whether there's a truthy value, you can do:

if (strValue) {
    //do something
}

If you need to check specifically for an empty string over null, I would think checking against "" is your best bet, using the === operator (so that you know that it is, in fact, a string you're comparing against).

if (strValue === "") {
    //...
}

Best Solution

Related Solutions

Javascript – Which “href” value should I use for JavaScript links, “#” or “javascript:void(0)”

Javascript – How to check for an empty/undefined/null string in JavaScript

Related Question