I think I would use a dictionary as a cache. If I can get the data from the cache all is good, if not make a request for the data, and cache it upon return for future use. Something like this, roughly speaking, there may errors in here, but this does compile. I’m also eliding over some other implementation details, such as initialization, views etc.
import Dict exposing (Dict)
import Http exposing (Error)
import Task exposing (Task)
type alias Cache =
Dict String String
type alias Model =
{ cache : Cache
, key : String
, locations : List String
}
model : Model
model =
{ cache = Dict.empty
, key = ""
, locations =
[ "foo", "bar", "baz" ]
-- get these via an API call, or load them via flags, etc
}
type Msg
= GetItem String
| GetAllItems (List String)
| GetItemFromCache String (Result Http.Error String)
update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
case msg of
GetAllItems locations ->
( model
, Cmd.batch
(List.map
(\key ->
Task.attempt (GetItemFromCache key) (getItem key model.cache)
)
locations
)
)
GetItem key ->
( model, Task.attempt (GetItemFromCache key) (getItem key model.cache) )
GetItemFromCache key result ->
case result of
Ok data ->
( { model | cache = Dict.insert key data model.cache }, Cmd.none )
Err err ->
-- add error handling here
( model, Cmd.none )
getItem : String -> Cache -> Task Http.Error String
getItem key cache =
case (Dict.get key cache) of
Just item ->
Task.succeed item
Nothing ->
Http.getString "https://path-to-api?query=key"
|> Http.toTask
