Ecosyste.ms: Awesome
An open API service indexing awesome lists of open source software.
https://github.com/noredink/elm-saved
A type keeping track of changes to a value since it was last saved.
https://github.com/noredink/elm-saved
Last synced: about 2 months ago
JSON representation
A type keeping track of changes to a value since it was last saved.
- Host: GitHub
- URL: https://github.com/noredink/elm-saved
- Owner: NoRedInk
- License: bsd-3-clause
- Created: 2018-04-14T19:36:49.000Z (over 6 years ago)
- Default Branch: master
- Last Pushed: 2018-11-28T03:17:18.000Z (about 6 years ago)
- Last Synced: 2024-05-08T23:24:51.967Z (8 months ago)
- Language: Elm
- Homepage: http://package.elm-lang.org/packages/NoRedInk/elm-saved/latest
- Size: 10.7 KB
- Stars: 1
- Watchers: 6
- Forks: 0
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# `Saved a`
A type keeping track of changes to a value since it was last saved.
This is great for building editing interfaces that keep track of whether the user has
made any changes.
## Dealing with an intial unsaved value
Suppose we're writing a text editing application.
`Saved a` assumes that a saved value we can revert to always exists.
For our text editing example such a value can for instance be an empty document.
If we're saving these documents to some backend, we might want to distinguish between this initial unpersisted value and a value that has been persisted to the backend.
One way to do this is to use different types for persisted and unpersisted documents.
For instance, let's assume a document that is persisted on the backend has an id, while one that's not persisted does not.
We can define separate types for documents in these different states:
```elm
type alias PersistedDoc =
{ id : Int
, title : String
-- More properties here
}
type alias UnpersistedDoc =
{ title : String
-- More properties here
}
type Model
= Persisted (Saved PersistedDoc)
| Unpersisted (Saved UnpersistedDoc)
```
When we perform the initial save, we can turn a `Saved UnpersistedDoc` to a `Saved PersistedCo` using the `map` function.
## Saving data to a server
Lets stay with the example of a text editing application a bit longer.
At some point we'll want to save a version of the document to a backend, keeping track of the progress of this operation and whether it results in a successful safe or not.
The `Saved a` type has no opinion on what it means for a value to be saved, but the [RemoteData](http://package.elm-lang.org/packages/krisajenkins/remotedata/latest) is perfect for this use case.
We can put the `Saved a` and `RemoteData e a` types next to each other on the model:
```elm
type alias Model =
{ doc : Saved Doc
, saveState : RemoteData Http.Error Doc
}
```
At this point it looks a bit like by using both `Saved a` and `RemoteData e a` we're duplicating state, but really the above solution precisely tracks the tree versions of a document that are relevant while the document is in the process being saved:
1. The last succesfully saved version, which is tracked by `Saved a`.
2. The version we're currently attempting to save, which is tracked by `RemoteData e a`.
3. The most recently edited version the user is seeing on the screen, which can already have diverged from the version we're currently saving. This version is also traced by `Saved a`.
Once our Http request responds that the save was successfull, we can use `setSaved` to update the last saved value of our document.