vikunja-api/docs/concepts.md

Architectural concepts

Vikunja was built with a maximum flexibility in mind while developing. To achive this, I built a set of easy-to-use functions and respective web handlers, all represented through interfaces.

CRUDable

This interface defines methods to Create/Read/ReadAll/Update/Delete something. In order to use the common web handler, the struct must implement this and the Rights interface.

The interface is defined as followed:

type CRUDable interface {
	Create(*User) error
	ReadOne() error
	ReadAll(*User) (interface{}, error)
	Update() error
	Delete() error
}

Each of these methods is called on an instance of a struct like so:

func (l *List) ReadOne() (err error) {
	*l, err = GetListByID(l.ID)
	return
}

In that case, it takes the ID saved in the struct instance, gets the full list object and fills the original object with it. (See parambinder to understand where that ID is coming from).

All functions should behave like this, if they create or update something, they should return the created/updated struct instance. The only exception is ReadAll() which returns an interface. Usually this is an array, because, well you cannot make an array of a set type (If you know a way to do this, don't hesitate to drop me a message).

Rights

This interface defines methods to check for rights on structs. They accept a User as parameter and usually return a bool.

The interface is defined as followed:

type Rights interface {
	IsAdmin(*User) bool
	CanWrite(*User) bool
	CanRead(*User) bool
	CanDelete(*User) bool
	CanUpdate(*User) bool
	CanCreate(*User) bool
}

When using the standard web handler, all methods except CanRead() are called before their CRUD counterparts. CanRead() is called after ReadOne() was invoked as this would otherwise mean getting an object from the db to check if the user has the right to see it and then getting it again if thats the case. Calling the function afterwards means we only have to get the object once.

Standard web handler

Errors

Error types with their messages and http-codes are set in models/error.go. If the error type implements HTTPError, the server returns a user-friendly error message when this error occours. This means it returns a good HTTP status code, a message, and an error code. The error code should be unique across all error codes and can be used on the client to show a localized error message or do other stuff based on the exact error the server returns. That way the client won't have to "guess" that the error message remains the same over multiple versions of Vikunja.

An HTTPError is defined as follows:

type HTTPError struct {
	HTTPCode int    `json:"-"` // Can be any valid HTTP status code, I'd reccomend to use the constants of the http package.
	Code     int    `json:"code"` // Must be a uniqe int identifier for this specific error. I'd reccomend defining a constant for this.
	Message  string `json:"message"` // A user-readable message what went wrong.
}