I have a structure that looks like this
type MediaFile struct {
ID string `json:"id"`
Secret string `json:"-"`
Title string `json:"title"`
}
I want to be able to change the script tag for Secret into json:"secret" when a condition is satisfied.
The struct MediaFile has been referenced a lot within other parts of the code, so using a different Struct with a different name isn't feasible.
I tried to use pointers like follows. Note that I have removed the definition of struct Mediafile as seen before in the following example.
type AlterMediaFile struct {
ID string `json:"id"`
Secret string `json:"secret"`
Title string `json:"title"`
}
type MediaFile struct {
*AlterMediaFile
}
But it resulted in me receiving a lot of promoted field errors since it's AlterMediaFile is basically just a nested class of MediaFile in this case.
So, is there any simple way for me to be able to alter the 'Secret' script tag from json:"-" to json:"secret" ?
You can not alter the 'Secret' script tag from json:"-" to json:"secret" at runtime.
However, you can use the omitempty option, json:"secret,omitempty", to specify that the field should be omitted from the encoding if the field has an empty value (in this case, an empty string).
When your condition is not satisfied, you can just simply set the Secret field to an empty string (this can be done with your database) and it will not show up in the json data.
You can write your own MarshalJSON/UnmarshalJSON methods.
type MediaFile struct {
ID string
Secret string
Title string
}
type jsonMediaFile struct {
ID string `json:"id"`
Title string `json:"title"`
}
type jsonSecretMediaFile struct {
*jsonMediaFile
Secret string `json:"secret"`
}
func (mf *MediaFile) MarshalJSON() ([]byte, error) {
jsonMF := jsonMediaFile{
ID: mf.ID,
Title: mf.Title,
}
if isNeedMarshalSecret() {
return json.Marshal(jsonSecretMediaFile{
jsonMediaFile: &jsonMF,
Secret: mf.Secret,
})
}
return json.Marshal(jsonMF)
}
I have written this piece of code. I can't figure out why it is giving empty fields when i run it. I have tried Uppercase variables. Still doesn't work.
package main
import (
"encoding/json"
"fmt"
)
type FirstName struct {
Name1 string
}
type SecondName struct {
Name2 string
}
type Person struct {
Details FirstName
MoreDetails SecondName
}
func main() {
var someGuy Person
var data = []byte(`{"details": {"firstName": "alan"}, "moreDetails": {"surName": "Turing"}}`)
json.Unmarshal(data, &someGuy)
fmt.Println(someGuy)
}
Your JSON to Go mapping is incorrect. To have automatic matching between struct fields and the JSON properties during the unmarshaling process, the field names (and not the name of their types) must match the properties in JSON (in a case in-sensitive manner):
type FirstName struct {
FirstName string
}
type SecondName struct {
SurName string
}
type Person struct {
Details FirstName
MoreDetails SecondName
}
With this, the output is (try it on the Go Playground):
{{alan} {Turing}}
If you want to keep those names in Go, another option is to provide a mapping between Go struct fields and JSON property names. For this you may use struct tags:
type FirstName struct {
Name1 string `json:"firstName"`
}
type SecondName struct {
Name2 string `json:"surName"`
}
Output will be the same. Try this one on the Go Playground.
For an introduction and more details about struct tags, see What are the use(s) for tags in Go?
So I have JSON like this
{"Name":"Jame","Age":6,"Original_Name":"Jameson"}
In order to get "Name" and "Age" in Go, I just need to use a corresponding struct
type Result struct {
Name string
Age int
}
But how do I get the field "Original_Name" since I cannot use underscore in go?
Does this work:
type Result struct {
Name string
Age int
Originalname string `json:"Original_Name"`
}
This question already has answers here:
My structures are not marshalling into json [duplicate]
(3 answers)
Closed 7 months ago.
I would like to create a JSON of a GatewayInfo where the type are defined like this:
type SpanInfo struct {
imsi string
network string
network_status string
signal_quality int
slot int
state string
}
type GatewayInfo []SpanInfo
The gateway information is created with:
var gatewayInfo = make(GatewayInfo, nb_spans)
To create the JSON, I use the json.Marshal function:
gatewayInfo := getGatewayInfo(spans)
log.Printf("Polling content: %s\n", gatewayInfo)
jsonInfo, _ := json.Marshal(gatewayInfo)
log.Printf("jsonInfo: %s\n", jsonInfo)
Unfortunately the result is not what I was expecting:
2015/02/09 13:48:26 Polling content: [{652020105829193 20801 Registered (Roaming) %!s(int=17) %!s(int=2) } {652020105829194 20801 Registered (Roaming) %!s(int=16) %!s(int=3) } {652020105829192 20801 Registered (Roaming) %!s(int=19) %!s(int=1) } {652020105829197 20801 Registered (Roaming) %!s(int=19) %!s(int=4) }]
2015/02/09 13:48:26 jsonInfo: [{},{},{},{}]
As we can see, the GatewayInfo instance has the SpanInfo, but in the JSON I have empty SpanInfo.
Your struct fields must be exported (field is exported if it begins with a capital letter) or they won't be encoded:
Struct values encode as JSON objects. Each exported struct field
becomes a member of the object
To get the JSON representation as probably expected change the code to this:
type SpanInfo struct {
IMSI string `json:"imsi"`
Network string `json:"network"`
NetworkStatus string `json:"network_status"`
SignalQuality int `json:"signal_quality"`
Slot int `json:slot"`
State string `json:"state"`
}
type GatewayInfo []SpanInfo
The json package can only serialize exported fields of your struct. Change your struct to start all fields with an uppercase letter so they can be included in the output:
type SpanInfo struct {
Imsi string
Network string
Network_status string
Signal_quality int
Slot int
State string
}
Read the documentation of json.Marshal() for details and more information.
This is not a new answer. It is just consolidation of comments on the
accepted answer.
From ORIGINAL Query
type SpanInfo struct {
imsi string
network string
network_status string
signal_quality int
slot int
state string
}
From Answer and comments - Please note that the first char of each field in struct is now in UPPER case along with json representation added to each field
type SpanInfo struct {
IMSI string `json:"imsi"`
Network string `json:"network"`
NetworkStatus string `json:"network_status"`
SignalQuality int `json:"signal_quality"`
Slot int `json:slot"`
State string `json:"state"`
}
I can't decode the json code below ... any ideas why it doesn't work ? See also play.golang
package main
import (
"encoding/json"
)
type LocationReadable struct {
District string
City string
State string
}
type Locale struct {
Location string
CountryCode string
CurrencyId string
CurrencySymbol string
LocationReadable LocationReadable
}
type Media struct {
Image string
Video string
}
type Variations struct {
FixedPrice float64
Media Media
Quantity int
}
type PaymentData struct {
PaymentName string
PaymentService string
}
type Payment struct {
Online PaymentData
Offline PaymentData
}
type Shipping struct {
ShippingService string
ShippingName string
ShippingCost float64
HandlingTimeMax int
DispatchTimeMin int
DispatchTimeMax int
ShippingAdditionalCost int
}
type Item []struct {
_version string
CategoryId string
Title string
Media Media
SellerId string
Locale Locale
ListingType string
Payment Payment
StartTime string
EndTime string
Shipping Shipping
TitleSlug string
Variations Variations
_fpaiStatus string
}
func main() {
itemInfoR := `{"locale":{"location":"51.51121389999999,-0.11982439999997041","countryCode":"GB","currencyId":"GBP","currencySymbol":"£","locationReadable":{"district":"City of Westminster","city":"London","state":"Greater London"}},"_version":"serving","categoryId":["Root","Cameras \u0026 Photo","Digital Cameras"],"title":"many pictures","media":{"image":["//lh5.ggpht.com/O_o_N6CFkClY5AV0-LqntpyFjor7Of4u23ZcK7lYwc2uY1ea7GWi61VDJZCB7UCb79svkjKPHIenqwEUhjHi0jdIQnnl6z_p03yktPUB1FBHezIQ","//lh6.ggpht.com/ih3q2d7CenGLPyupH9FpfsoJQWQpw1i8wWA2Kd26bFnSF2fbnKyGU9WePIhCgEeqw5p6YMVmFi1c9oS0Ag93aF_oZ3ZiwK7fQuSYIrZ9VhgXbrTHkw","//lh6.ggpht.com/7RJRsapsnwWL3_KiLIjMz4QojDzUvsztXtvKTFvIfde_AHccDnOibAvXRN73tTB4SeHzlj8S1LWxbYwwWFGn9elfCKdSb8BUIU5QJY1LO791HutQ","//lh6.ggpht.com/qAtjgyHAB734Ox_4NC_fa-ZRqrCjCmJu0Tp8bo-HMO88duv8l4hhuv2REBkB--yneFzOL7annecVlGty-YsKouondiOFVnAZWzjpdrfsGfbL6wh2","//lh3.ggpht.com/dWUbASepwHF4lHaXIPnpv4BNm2pCml9MlJt7s86s1cpu-PsYNmS0yQmKFKTM38q_oMLW_YJMJ19civ2gVViKAGYcZylRW7jN3w77AJvhzS6JE2g","//lh6.ggpht.com/9aXLmPRVeZnxkwvNb3mWTF8kvfEY_lho_lOVVc9AbNqLb8GQmiS_XXVZ3OKqMv2pxgYSayMYPPRh6ACYyh0H8KtS8mPD6MKUkEajwxkTtp5Q4Lo","//lh3.ggpht.com/FG_QXZPHJ2tTYwI_t5Fg1KqivglVg9RlJn0JRsu9Ox8vJ7IcBirb2IV_I1LL_WVOMxfTuBBSDLMlrw9v0MCAdmnPCR29sCbRGjhm6zEfIH-3q2QSdw","//lh4.ggpht.com/Y23DqORrVkM2m55f-rq5_BBrlkvQg4uX7AsAt-ixhMobjK_SFgFaDfktgLhkNsyKwSr9HcF8iiGY3Nw0xOKXG1sn6wyAWg_qsolmKjVOrM5V5mIR","//lh6.ggpht.com/mQ62Ly-DjMKPMzU1OcSPJ7SLBqym0uBjawlkTHfmb-HOKaD56dnitk1duwPFJVdbi0GUpd63RQvr2VMpHp6S1OQ3di-hq4-JPeRoS5FJzksXSvW_","//lh3.ggpht.com/dqWjWPcNsvlR1tMC_agizX19f9MDiNGWFYTYVn4kjJxzIIkEe0mLzNcvS62zVJxAOaitT-IgaUfZ-Ze23BgzbqYY-l600i_LbVe35Uinz6sXIyoB","//lh6.ggpht.com/xhSdFc9uHgghs_6gf3seUWYM-PG2oLmjTrpF7ptEEMqaIrQIa8VPfC6tXE7f3M13eZvDXYqMW_k0AHO5vwCEPNp-iObixskd_lBaKNfz3MH3SNQ","//lh5.ggpht.com/kYeoKPoZGJCow-G1FhnD8kzVjNjbQA8-Kyj8eAh0HL-fMZX9tTeFPQikTZdSU0kks4-5Ui54cZF2CjGut9vfMJAVDKIq3T-bAQewCxvfl2120tH5zQ","//lh5.ggpht.com/4qUl3d-G9EPBzcYKrimNsWhQw7CmONV0jgfVhxFgB9mEU_QLRCyNJTWs2A3xf6wc7AUF2DXrKEkoX-SNLMZ6s-O4aXXV9WOjOPcWdAYreMRBld0E","//lh5.ggpht.com/z-0C4G6EWYkelAF1LjPfl_UQcsp92H4joIPt8NfsOl0nPJ2VpzZYahWadKqTLfl6kq3C6aDBcwfGQyMWSozYoZIAOAW0yRvZrwxia321PlsKTxbZ","//lh4.ggpht.com/U7I12JrDYmMC_pUXpw8DVBjBilU67BvbM8qT8gJE0bQfkhHo7FOdMttiz3syP5IR-LyO4J1WBlfmZjvMjRr4GIBt4o3Vqp-hKz7q2_OGwGtsN5s","//lh3.ggpht.com/fF2XWEtqG23ybhzClhC_p8gvKJalf1vg7k3H7UkuAaIVubil7EgOvJUCwAZk2KiCtlPYp1E5Ep2xaxZjJRmg5EFSEAjqlMHJS_Wd1Bcje6xre4s","//lh3.ggpht.com/jgOebMihBoIZvHE4EOklJvZ_k-9egjNIlUKfKFcLkvXJs8g2FXjPvdFUbwqGrkHrMtyis8uOvgt-E51Vm11hq4bieh7h0cegca0VI4vFtFaAemU","//lh3.ggpht.com/MOrI-zKNMNrQE_aHj5hzbojP3T0hEMJKK6K8UO3e1NBC-nkcQeIM1QnvtJdT_G-W4e7-qv4BiqwdWcNHBpZXOmmX3tcuYEV8u_ANEoa9_aUIfeyg","//lh6.ggpht.com/SyIS5sGOkTG7k_jFF14wzH9Evrblv6o4pHBI6z6X070-xhAeyut_kRO6xHtDID4KLcWFvItjQy-plPcJ6K1T9tlFOrtaryEPvuAYdMVx8e0TTw","//lh6.ggpht.com/2Pp9kLYFhDT3USwHinU5OxnzcWWOLI0nOWe29gOD5KMzyEcXoHkTN-AutJV9M8F_9eqAP379XB9O1d0BWPanhr-MguzKxfHeUvYTs6yHzDkxyfe0NA","//lh4.ggpht.com/7aofqklSkF3AMDfF19yqsA9J3EfEiKy1NdOelEGKNnW0Cv5tGEpq2PF_jZO1MVoBbrrmVVRv0Tdq7I8KyZbIlyHdbTs1jMl7dEFqVMvsPcyaORyHlQ","//lh4.ggpht.com/anYJHqkMCkuhmIHQTBspLtWcDTyx1ZRe84_q5pAgVEOVmsKkaKhS725N4YFoj2zpJrBP7iTC2vf1GUtrp6H7kkm8c1k6zkW6I_Gf5f9A3re_I8Ex","//lh3.ggpht.com/OtSw0rU-DvfoXgoWrQdkln6Kz7O14TF9qrPNJSGJnZLeDqUEctOn1DT09pdwwVpNQV-cXmVYQL-PX4XPhpZLWH1ciSkVT6WHNmTz1D9pHphBwJUv","//lh3.ggpht.com/cTCZnXPIjI-EO2bvQdLgeoSLOSlMFcv805n347Zyci9XDYUdcVDC_5H7SFVYDr4pC5HtQDYnrOHL6AinLW7hWtfSCLlvVhVUNQ-DlDn0NwZ-1iCO-g","//lh4.ggpht.com/i-mL_JcF9rwjQq6HnuKzuAHU41_UGxQ62IOPZvaDrATXaPFbhe-EbT7ZIpboyNA5PXRCsxNsZ9hu58edRvNs5ScgKN8Lg-00J2LhlwMAbdEsv7b0nw","//lh6.ggpht.com/D_YV2BG1WWwl67xNloP3sxzRkqhcVTgJi58L-A8nLrOcMR_tBqLz4fHEGQ-qiNcG_-32MNy3dlSPWrTBKzBcweJxgMnRVet5yuGfelUlwehDtXX_3w"],"video":[]},"sellerId":"mihai","listingType":"fixedPrice","payment":{"online":[{"paymentName":"PayPal","paymentService":"paypal"}],"offline":[{"paymentName":"Pay on Pick-up","paymentService":"payOnPickup"}]},"startTime":"2014-01-04T10:02:18+00:00","endTime":"2014-04-04T10:02:18+00:00","shipping":[{"shippingService":"economy","shippingName":"Economy","shippingCost":1.0,"handlingTimeMax":4,"dispatchTimeMin":1,"dispatchTimeMax":10,"shippingAdditionalCost":"2"},{"shippingService":"localPickup","shippingName":"Local Pick-Up","shippingCost":0.0,"handlingTimeMax":2,"dispatchTimeMin":0,"dispatchTimeMax":0,"shippingAdditionalCost":"0"}],"titleSlug":"many-pictures","variations":[{"fixedPrice":222999.0,"media":{"image":["//lh6.ggpht.com/ih3q2d7CenGLPyupH9FpfsoJQWQpw1i8wWA2Kd26bFnSF2fbnKyGU9WePIhCgEeqw5p6YMVmFi1c9oS0Ag93aF_oZ3ZiwK7fQuSYIrZ9VhgXbrTHkw","//lh6.ggpht.com/9aXLmPRVeZnxkwvNb3mWTF8kvfEY_lho_lOVVc9AbNqLb8GQmiS_XXVZ3OKqMv2pxgYSayMYPPRh6ACYyh0H8KtS8mPD6MKUkEajwxkTtp5Q4Lo","//lh3.ggpht.com/FG_QXZPHJ2tTYwI_t5Fg1KqivglVg9RlJn0JRsu9Ox8vJ7IcBirb2IV_I1LL_WVOMxfTuBBSDLMlrw9v0MCAdmnPCR29sCbRGjhm6zEfIH-3q2QSdw"],"video":[]},"quantity":1121,"Brand":"Bell \u0026 Howell"},{"fixedPrice":211.0,"media":{"image":["//lh6.ggpht.com/qAtjgyHAB734Ox_4NC_fa-ZRqrCjCmJu0Tp8bo-HMO88duv8l4hhuv2REBkB--yneFzOL7annecVlGty-YsKouondiOFVnAZWzjpdrfsGfbL6wh2","//lh3.ggpht.com/FG_QXZPHJ2tTYwI_t5Fg1KqivglVg9RlJn0JRsu9Ox8vJ7IcBirb2IV_I1LL_WVOMxfTuBBSDLMlrw9v0MCAdmnPCR29sCbRGjhm6zEfIH-3q2QSdw","//lh6.ggpht.com/9aXLmPRVeZnxkwvNb3mWTF8kvfEY_lho_lOVVc9AbNqLb8GQmiS_XXVZ3OKqMv2pxgYSayMYPPRh6ACYyh0H8KtS8mPD6MKUkEajwxkTtp5Q4Lo","//lh3.ggpht.com/MOrI-zKNMNrQE_aHj5hzbojP3T0hEMJKK6K8UO3e1NBC-nkcQeIM1QnvtJdT_G-W4e7-qv4BiqwdWcNHBpZXOmmX3tcuYEV8u_ANEoa9_aUIfeyg"],"video":[]},"quantity":2,"Brand":"Fujifilm"},{"fixedPrice":22.0,"media":{"image":["//lh3.ggpht.com/jgOebMihBoIZvHE4EOklJvZ_k-9egjNIlUKfKFcLkvXJs8g2FXjPvdFUbwqGrkHrMtyis8uOvgt-E51Vm11hq4bieh7h0cegca0VI4vFtFaAemU","//lh3.ggpht.com/MOrI-zKNMNrQE_aHj5hzbojP3T0hEMJKK6K8UO3e1NBC-nkcQeIM1QnvtJdT_G-W4e7-qv4BiqwdWcNHBpZXOmmX3tcuYEV8u_ANEoa9_aUIfeyg","//lh4.ggpht.com/anYJHqkMCkuhmIHQTBspLtWcDTyx1ZRe84_q5pAgVEOVmsKkaKhS725N4YFoj2zpJrBP7iTC2vf1GUtrp6H7kkm8c1k6zkW6I_Gf5f9A3re_I8Ex"],"video":[]},"quantity":12,"Brand":"Gateway"}],"_fpaiStatus":"published"}`
itemInfoBytes := []byte(itemInfoR)
var ItemInfo Item
er := json.Unmarshal(itemInfoBytes, &ItemInfo)
if er != nil {
panic(er)
}
}
Here's a fixed version of it: http://play.golang.org/p/w2ZcOzGHKR
The biggest fix that was needed is when Unmarshalling an array, that property needs to be an array/slice in the struct as well.
For example:
{ "things": ["a", "b", "c"] }
Would Unmarshal into a:
type Item struct {
Things []string
}
And not into:
type Item struct {
Things string
}
The other thing to watch out for when Unmarshaling is that the types line up exactly. It will fail when Unmarshalling a JSON string representation of a number into an int or float field -- "1" needs to Unmarshal into a string, not into an int like we saw with ShippingAdditionalCost int
Determining of root cause is not an issue since Go 1.8; field name now is shown in the error message:
json: cannot unmarshal object into Go struct field Comment.author of type string
You JSON doesn't match your struct fields: E.g. "district" in JSON and "District" as the field.
Also: Your Item is a slice type but your JSON is a dict value. Do not mix this up. Slices decode from arrays.
Just in case you're looking for an answer to this from an AWS perspective, particularly if you're trying to use UnmarshalListOfMaps() on the items coming back from a DynamoDB query(), then watch out for a simple typo I made.
Given that this function UnmarshalListOfMaps() takes in...a list of maps :-) then it needs to unmarshal into a List of whatever struct you're trying to build, and not just the plain struct itself. This was throwing me off because I was trying to start by querying for something that should only return one row.
movie := Movie{}
// Run the DynamoDB query
resp, err := session.Query(input) // type QueryInput
if err != nil {
log.WithError(err).Error("Error running DynamoDB query")
}
// Unmarshal all the attribute values into a Movie struct
err = dynamodbattribute.UnmarshalListOfMaps(resp.Items, &movie); if err != nil {
log.WithError(err).Error("Error marshaling DynamoDB result into Movie")
return link, err
}
The problem is in the first line. It should be movies := []Movie{} and then the reference &movie needs to change to &movies as well. If you leave it just as it is above, then the AWS Go SDK will throw this error:
cannot unmarshal list into Go value of type (etc).
If you ever face this while typing yml file not copy-pasting, it might be a problem with your yml file - mine was wrong indent.
This happened while making pipeline on concourse.