Re: [go-nuts] Preserving extra properties using JSON unmarshal / marshal?

['Eric Johnson' via golang-nuts]

Thanks for the pointers.

I was hoping for an easier answer. Maybe will look into patching stdlib.

Eric.


On Sat, Feb 22, 2020 at 1:15 AM Brian Candler  wrote:

> Looks like your thoughts are the right ones:
>
> https://stackoverflow.com/questions/33436730/unmarshal-json-with-some-known-and-some-unknown-field-names
>
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Re: [go-nuts] Preserving extra properties using JSON unmarshal / marshal?

[Brian Candler]

Looks like your thoughts are the right ones:
https://stackoverflow.com/questions/33436730/unmarshal-json-with-some-known-and-some-unknown-field-names

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Re: [go-nuts] Preserving extra properties using JSON unmarshal / marshal?

['Eric Johnson' via golang-nuts]

Understand all that. It doesn't help.

Asking the question a different way, as concrete code always clarifies. For 
something like the following snippet of code:

const testJSON = `{
"first_name": "first",
"last_name": "last",
"favorite_color": "orange",
"age": 92
}`

func TestUnmarshalling(t *testing.T) {
var res struct {
FirstName string `json:"first_name"`
LastName  string `json:"last_name"`
}
err := json.Unmarshal([]byte(testJSON), )
assert.NoError(t, err)
out, err := json.MarshalIndent(, "", "\t")
assert.NoError(t, err)
assert.Equal(t, testJSON, string(out))
}

Is there anything I can do to the "res" struct" to preserve the 
"favorite_color" and "age" properties from the original JSON, so that the 
final assert.Equal() passes? Ideally, as I indicated in the original post, 
it would be something along the lines of an additional struct member that 
acts as the catch-all for any values not found for the struct. (hence the 
line "Extras map[string]interface{} `json:",extra" that I put in my 
example.)

Stepping through the standard library, it seems pretty clear that the 
standard library simply discards JSON properties that it doesn't map to 
fields. I think the crucial lines 
 (decode.go, 753-769) 
indicate that if a field is not found, no target value ("subv") is set, and 
then the resulting data is discarded.

Since the standard library doesn't support it, I'm wondering if there are 
any other reliable JSON encode / decode libraries out there that might?

I have three options, that I can tell:

   - Find an alternate library that supports something like this (hence the 
   post)
   - Use the standard library by implementing the Unmarshaler interface on 
   the struct, use normal unmarshaling for the known fields, then also 
   unmarshal as a map[string]interface{}, remove all the fields that I don't 
   want, and store the results in the "Extra" field myself. This will result 
   in double-parsing each struct and a lot of extra boilerplate code. Then 
   also need to do appropriate somethings to implement Marshal as well.
   - Fork the standard library JSON package, add the support myself, and 
   submit it back as a possible enhancement(!).
   
Using the standard library as is seems like a bad option, given the extra 
boilerplate that would be required for each struct. I'm hoping someone has 
already made an implementation that does this!

Eric.

On Friday, February 21, 2020 at 1:41:20 PM UTC-8, Chris Burkert wrote:
>
> Take a Look at 
> https://blog.golang.org/json-and-go:
>
> The json package uses map[string]interface{} and []interface{}values to 
> store arbitrary JSON objects and arrays; it will happily unmarshal any 
> valid JSON blob into a plain interface{} value. The default concrete Go 
> types are:
>
>- bool for JSON booleans,
>
>
>- float64 for JSON numbers,
>
>
>- string for JSON strings, and
>
>
>- nil for JSON null.
>
>
> Does this help?
>
> 'Eric Johnson' via golang-nuts > 
> schrieb am Fr. 21. Feb. 2020 um 19:00:
>
>> If I've got a structure like this:
>>
>> type jsonData struct {
>> FirstName string `json:"first_name"`
>> LastName  string `json:"last_name"`
>> }
>>
>> I can marshal / unmarshal JSON as:
>> {
>>   "first_name": "first",
>>   "last_name": "last"
>> }
>>
>> What if my input JSON is this:
>> {
>>   "first_name": "first",
>>   "last_name": "last",
>>   "favorite_color": "orange",
>>   "age": 92
>> }
>>
>> Is there an existing library to have a structure that's something like 
>> this:
>>
>> type jsonData struct {
>> FirstName string `json:"first_name"`
>> LastName  string `json:"last_name"`
>> Extrasmap[string]interface{} `json:",extras"`
>> }
>>
>> Such that a JSON unmarshal and marshal will preserve the data of the 
>> original JSON?
>>
>> I think I can probably make something work with the standard library, 
>> except that it will require extra marshaling / unmarshaling steps that will 
>> be annoying to reproduce for each structure that needs to capture extra 
>> data. So I'm hoping there's a better solution?
>>
>> Eric
>>
>>
>> -- 
>> You received this message because you are subscribed to the Google Groups 
>> "golang-nuts" group.
>> To unsubscribe from this group and stop receiving emails from it, send an 
>> email to golan...@googlegroups.com .
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>>  
>> 
>> .
>>
>

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Re: [go-nuts] Preserving extra properties using JSON unmarshal / marshal?

[Chris Burkert]

Take a Look at
https://blog.golang.org/json-and-go:

The json package uses map[string]interface{} and []interface{}values to
store arbitrary JSON objects and arrays; it will happily unmarshal any
valid JSON blob into a plain interface{} value. The default concrete Go
types are:

   - bool for JSON booleans,


   - float64 for JSON numbers,


   - string for JSON strings, and


   - nil for JSON null.


Does this help?

'Eric Johnson' via golang-nuts  schrieb am
Fr. 21. Feb. 2020 um 19:00:

> If I've got a structure like this:
>
> type jsonData struct {
> FirstName string `json:"first_name"`
> LastName  string `json:"last_name"`
> }
>
> I can marshal / unmarshal JSON as:
> {
>   "first_name": "first",
>   "last_name": "last"
> }
>
> What if my input JSON is this:
> {
>   "first_name": "first",
>   "last_name": "last",
>   "favorite_color": "orange",
>   "age": 92
> }
>
> Is there an existing library to have a structure that's something like
> this:
>
> type jsonData struct {
> FirstName string `json:"first_name"`
> LastName  string `json:"last_name"`
> Extrasmap[string]interface{} `json:",extras"`
> }
>
> Such that a JSON unmarshal and marshal will preserve the data of the
> original JSON?
>
> I think I can probably make something work with the standard library,
> except that it will require extra marshaling / unmarshaling steps that will
> be annoying to reproduce for each structure that needs to capture extra
> data. So I'm hoping there's a better solution?
>
> Eric
>
>
> --
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> "golang-nuts" group.
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> 
> .
>

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[go-nuts] Preserving extra properties using JSON unmarshal / marshal?

['Eric Johnson' via golang-nuts]

If I've got a structure like this:

type jsonData struct {
FirstName string `json:"first_name"`
LastName  string `json:"last_name"`
}

I can marshal / unmarshal JSON as:
{
  "first_name": "first",
  "last_name": "last"
}

What if my input JSON is this:
{
  "first_name": "first",
  "last_name": "last",
  "favorite_color": "orange",
  "age": 92
}

Is there an existing library to have a structure that's something like this:

type jsonData struct {
FirstName string `json:"first_name"`
LastName  string `json:"last_name"`
Extrasmap[string]interface{} `json:",extras"`
}

Such that a JSON unmarshal and marshal will preserve the data of the 
original JSON?

I think I can probably make something work with the standard library, 
except that it will require extra marshaling / unmarshaling steps that will 
be annoying to reproduce for each structure that needs to capture extra 
data. So I'm hoping there's a better solution?

Eric


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