books/models/README.md

# Models

The `models` root folder contains all the model files, i.e. files containing all
the models. **Models** here, refers to the classes that handle the data, its
validation and updation and a bunch of other stuff.

Each model directly or indirectly extends the `Doc` class from
`fyo/model/doc.ts` so for more info check that file and the associated types
in `fyo/model/types.ts`.

A model class can used even if the class body has no content, for example
`PurchaseInvoiceItem`. Else the model used will default to using `Doc`. The
class can also be used to provide type information for the field types else they
default to the catch all `DocValue` example:

```typescript
class Todo extends Doc {
  title?: string;
  date?: Date;
  completed?: boolean;
}
```

While this has obvious advantages, the drawback is if the underlying fieldtype
changes this too will have to be changed.

The data stored by the models is decided by the schema passed to it's
constructor. Check `schemas/README.md` for info on this.

## Adding Stuff

When adding stuff to `models/**` make sure that it isn't importing any Vue code
or other frontend specific code globally. This is cause model file tests will
directly use the the `Fyo` class and will be run using `mocha` on `node`.

Importing frontend code will break all the tests. This also implies that one
should be wary about transitive dependencies.

It should also not import the `Fyo` object (singleton) from `src`, where ever
`fyo` is required in models it should be passed to it.

_Note: Frontend specific code can be imported but they should be done so, only
using dynamic imports i.e. `await import('...')`._

## Regional Models

Regional models should as far as possible extend the base model and override
what's required.

They should then be imported dynamicall and returned from `getRegionalModels` in
`models/index.ts` on the basis of `countryCode`.