Decode Json Array with objects in Elm

问题:

I recently tried to get data from server with Elm's Http module and i'm stuck with decoding json to custom types in Elm.

My JSON looks like that:

[{     "id": 1,     "name": "John",     "address": {         "city": "London",         "street": "A Street",         "id": 1     } }, {     "id": 2,     "name": "Bob",     "address": {         "city": "New York",         "street": "Another Street",         "id": 1     } }] 

Which should be decoded to:

type alias Person = {  id : Int,  name: String,  address: Address }  type alias Address =  {  id: Int,  city: String,  street: String  } 

What i found so far is that i need to write a decoder function:

personDecoder: Decoder Person personDecoder =   object2 Person     ("id" := int)     ("name" := string) 

That for the first two properties but how i integrate the nested Address property and how combine this to decode the list?

回答1:

You first need an Address Decoder similar to your Person Decoder

Edit: Upgraded to Elm 0.18

import Json.Decode as JD exposing (field, Decoder, int, string)  addressDecoder : Decoder Address addressDecoder =   JD.map3 Address     (field "id" int)     (field "city" string)     (field "street" string) 

Then you can use that for the "address" field:

personDecoder: Decoder Person personDecoder =   JD.map3 Person     (field "id" int)     (field "name" string)     (field "address" addressDecoder) 

A list of persons can be decoded like this:

personListDecoder : Decoder (List Person) personListDecoder =   JD.list personDecoder 

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