# Model Constraints

# Overview

Our first example was pretty basic and in our second one we're only going to add a bit but they are important changes to understand:

  dbOffset: 'authenticated',
  localPrefix: 'in.the.tree',
  plural: 'peeps',
  audit: true
export class Person extends Model {
  @property public name: string;
  @property public age: number;
  @property public gender?: "male" | "female" | "other";

Maybe not surprisingly the "model constaints" are meta properties about your model as a whole (versus on a specific property). Let's review the options highlighted above ...

# Database Offseting

The dbOffset property tells Firemodel that all Person records should be saved to the database off of the "authenticated" data path. This string can contain both static paths and dynamic paths. The dynamic paths are denoted by prefixing the offset with a colon. Here are two examples:

// static prefix
@model({ dbOffset: "foo/bar" })
export class Anything extends Model {}

and as a dynamic path example:

// dynamic prefix
@model({ dbOffset: ":foo/bar" })
export class Anything extends Model {}

in the dynamic prefix example, it is assumed that the model has a property named foo and that the records will be stored in the database according to the value of the foo property. For more details on why you might want to use dynamic paths refer to the section Modeling → Dynamic Paths, if you just want to know how to run queries or setup watchers on models with dynamic paths then check out: Using → Dynamic Paths

# Frontend State Management

The localPrefix / localPostfix properties are used to help get Watch events into the right part of the client state management tree. To understand how they effect to the resultant localPath values found in the dispatched events we need to distinguish between the Watch of a Record versus a List. So, given a model defined as:

@model({ localPrefix: "foo/bar", localPostfix: "baz" })
export default class Person extends Model {...}

when watched in a client app like this:

await Watch.record(Person, "1234").start();

The resulting dispatches (e.g., RECORD_ADDED, RECORD_CHANGED, etc.) will have a localPath property of: /foo/bar. This may be surprising at first but it makes sense when you consider that in a majority of cases you are watching on a record (versus a list) when you only want a single record of that type.

Bear in mind that there could be some edge cases where this isn't the case and for these you should use a dynamic notation on one of the properties of the model (typically the "id"). By example if the localPrefix had been foo/bar/:id then it would have resolved the dbPath to foo/bar/1234.

Note: if no localPrefix is set for a given model and there is a record based watcher placed on the database, the localPath will be set to the singular model name

In all Record-based Watch's the localPostfix property is ignored but List-based Watch's are a bit different. Using our example above as the template, imagine:

await Watch.list(Person).all().start();

In this case, there may be several records returned initially as a RECORD_ADDED dispatch. For the record of id "1234" the dispatch payload would include:

  id: "1234"
  localPath: "foo/bar/people/baz",
  // ...

Unfortunately our use of an explicit value for localPostfix is maybe a bit confusing. Typically you would NOT set this value and then the type of list query type would determine the postfix for you. The default value for postfix is "all" and the localPath becomes foo/bar/people/all.

This fits into a very standard convention you find on a lot of frontend state management frameworks which allows for the primary "data" for a given model to be offset on .all or comparable which allows the base node (aka, foo/bar/people in this example) to contain getters which modify or filter the base data. This base node can also contain various meta attributes. For instance, let's assume you have a product catalog that is divided by region but a customer travels between two of these regions. You might imagine the following state tree:

products: {
  all: [ ... ], // the result of the two Watchers below
  currentRegion: "abc",
  previousRegion: "def",
  current: [ ... ], // a GETTER which filters to the "currentRegion"

Where you are populating the products/all property with:

Watch.list(Product).where("region", currentRegion).start();
Watch.list(Product).where("region", previousRegion").start();

# Other Model Constraints

  1. plural - by default Firemodel will pluralize your model name using standard rules. It should get it right most of the time but if you want to override this you can here. The reason the plural name is brought up is that the plural name is used in the storage path for both Firebase and your frontend state management.
  2. audit - in cases where the given model holds very sensitive data you may want to opt-in to having all changes audited. For more on this see the Auditing subsection in the Using section.
Last Updated: 10/2/2019, 3:31:55 PM