Default values

Summary

In this lesson, we explore the defaultsTo property in Waterline models, which allows setting default values for attributes when a record is created without explicitly providing them. This ensures attributes always have a meaningful fallback instead of being null. The lesson demonstrates how to define defaultsTo values, create records, and verify them in the database. It also clarifies that defaultsTo applies only during creation, not updates.

Transcript

So apart from the five basic types you can set for a Waterline attribute, there are additional guarantees you can provide to ensure its type. One of them is the defaultsTo property, which I personally like.

defaultsTo lets you assign a default value to an attribute when a record is created and that attribute isn't explicitly provided. This is great because it ensures the attribute never ends up as null unless intended.

Let's set this up in our User model. Suppose we want to make sure every user has an age, even if they don't provide one. We can do this by modifying the age attribute:

age: {
  type: 'number',
  defaultsTo: 18
}

Now, if a user signs up and doesn’t specify their age, it will automatically default to 18. Let's test this by creating a user without an age:

await User.create({
  firstName: 'Hansel',
  lastName: 'Grimm'
}).fetch();

If we check the database, we’ll see that the age attribute is set to 18 even though we didn’t provide it. Other unspecified attributes, like isAdmin, remain null unless they also have a defaultsTo value.

Now, let’s try setting a default for isAdmin:

isAdmin: {
  type: 'boolean',
  defaultsTo: false
}

Now, creating a user without specifying isAdmin will automatically set it to false. However, default values can still be overridden when explicitly provided:

await User.create({
  firstName: 'Bin',
  lastName: 'Doing',
  isAdmin: true
}).fetch();

If we check the database, isAdmin will be true because we specified it, while attributes we didn’t set will still get their default values.

One important thing to note: defaultsTo only applies when creating a record, not when updating. If you update a record and don’t provide a value for an attribute, the default won’t be re-applied.

In summary, defaultsTo is a great way to ensure attributes always have meaningful values, reducing the risk of unexpected null values while following your business logic.