I have a struct -
type User struct {
Uid string `firestore:"uid"`
FcmToken string `firestore:"fcmtoken"
}
How do I convert It to map using json.Marshal(user) ,
I know it can be done when struct fields are annotated with json:"fieldname" but I don't know how to do the same when it is annotated with firestore, or is it even possible?
I have used the word annotation, which may not be what it is called, please correct me!
A field tag can contain multiple key/value pairs. See the struct tag documentation for more details.
Edit the field tags to include whatever JSON configuration you want:
type User struct {
Uid string `firestore:"uid" json:"uid"`
FcmToken string `firestore:"fcmtoken" json:"tid"`
}
It is not possible to make the JSON package use the firestore tags or vice versa.
Related
I use AWS Lambda with DynamoDB using golang.
My DynamoDB table use lowercase attribute names such as id or name.
In Go, if I want to be able to marshal a struct correctly, I have to name fields starting with a capital letter.
type Item struct {
ID string
Name string
}
To put an item into my DynamoDB table, I have to marshal it into a map[string]*dynamodb.AttributeValue, using dynamodbattribute.MarshalMap function.
item := Item{
ID: "xxxx",
Name: "yyyy"
}
av, _ := dynamodbattribute.MarshalMap(item)
Of course, this will create a map using names written as ID and Name, which are incompatible with id and name from the dynamodb table.
Reading the documentation, I found that you can use a custom encoder, and enable json tags.
type Item struct {
ID string `json="id"`
Name string `json="name"`
}
func setOpts(encoder *dynamodbattribute.Encoder) {
// Not sure which one I sould set
// So I set them both :)
encoder.SupportJSONTags = true
encoder.MarshalOptions.SupportJSONTags = true
}
func main() {
encoder := dynamodbattribute.NewEncoder(setOpts)
encoder.Encode(...)
}
But here the encoder.Encode() method is only used to create a dynamodb.AttributeValue, and not a map[string]*dynamodb.AttributeValue.
Is there a way to use a custom encoder with MarshalMap? Or am I using it in a wrong way?
EDIT:
Okay so as Zak pointed out, there is a dynamodbav tag that can be used.
I also found out that I was using json tags in a wrong way. I should use the syntax json:"id" instead of json="id".
Indeed, DynamoDB SDK uses the json tag if available, and this one can be overrided by the dynamodbav.
So all I had to do was to make my structure looks like this and it worked
type Item struct {
ID string `json:"id"`
Name string `json:"name"`
}
Dynamo's built in marshalling, from MarshalMap(...) can support struct tags, similar to json.
You can add them to the type that you are marshalling, like so:
type Item struct {
ID string `dynamodbav:"id"`
Name string `dynamodbav:"name"`
}
See the docs here
I'm trying to decode a json response with a struct type. An instance of the object i'm trying to decode looks as follows:
{
"title": "Some Title",
"views": 344,
"profiles": {
"customField": "somevalue",
"customField2:" :somevalue"
}
}
The golang struct is the following:
type Topic struct {
Title string `json:"title"`
Views string `json:"views"`
Profiles string `json:"profiles"`
}
As you can see, the "Profiles" attribute is a string, since the profiles object is unknown, as the fields inside it can be dinamically defined.
I'm trying to decode this with:
json.NewDecoder(response.Body).Decode(result)
Where result is of type Topic, but isn't working. What type should the "Profiles" attribute be in order to correctly decoding the answer?
Thanks!
Reading the comment it's clear that profiles value could be of any type, for this reason I suggest you to declare the Profiles type as a map[string]interface{}.
Topic becomes:
type Topic struct {
Title string `json:"title"`
Views int32 `json:"views"`
Profiles map[string]interface{} `json:"profiles"`
}
Check out https://github.com/mitchellh/mapstructure
The readme has an answer you probably look for.
problem is if you have configuration or an encoding that changes slightly depending on specific fields.
Perhaps we can't populate a specific structure without first reading the "type" field from the JSON. We could always do two passes over the decoding of the JSON (reading the "type" first, and the rest later). However, it is much simpler to just decode this into a map[string]interface{} structure, read the "type" key, then use something like this library to decode it into the proper structure.
If profiles can vary you should take json.RawMessage here. Internally it is a []byte which late can be unmarshalled into other types, e.g. depending on values of the outer document.
See https://golang.org/pkg/encoding/json/#RawMessage and the examples.
The Profiles should be a struct and initiated along with the container, in this case I assume it's a Status, such as FB status or Tweet, I've made an example here https://play.golang.org/p/tG90idakLP
Remember to instantiate the new profiles inside a newly created status, before you start unmarshalling.
I'm writing an application in Go that will recieve two forms of JSON:
Example 1:
{"book_data":{"title":"book-title","page_number":457}}
Example 2:
{"book_data":{"collection":214},"books":{"data":[{"title":"book-title","page_number":457},{"title":"book-title","page_number":354}]}}
I thought that I could create a struct like the following and unmarshal JSON into it:
type Book struct {
Title string `json:"title"`
PageNumber int `json:"page_number"`
}
but that only works for the first example.
How can I handle JSON from both examples?
You can first unmarshal partly in json.RawMessage to next decide depending of unmarshalled payload. And you also can just unmarshal in more generic structure. Something like
type Book struct {
Title string `json:"title"`
PageNumber int `json:"page_number"`
}
type BookShelf struct {
BookData struct {
Book
Collection int `json:"collection"`
} `json:"book_data"`
Books struct {
Data []Book `json:"data"`
} `json:"books"`
}
which for me looks readable, meaningful and handy enough for further processing.
Why not unmarshal to a map[string]interface{} and then use the result to see which form you need to handle? You can then deserialize with a specific struct type for each form.
Another way would be to use the following package to check for differing attributes, so you can decide which struct to use for the real unmarshaling.
https://github.com/go-xmlpath/xmlpath/tree/v2
You can unmarshal to map because your key is string and value may be anything like - map[string]interface{}. If you are not sure any data type or value then use interface{} beacause it can store any value. Then use result to see which form it is, And deserialize to specific struct type.
Another way to convert JSON to go struct is use this tool.
https://mholt.github.io/json-to-go/
I'd like to marshal part of this struct:
type ValueSet struct {
Id string `json:"id" bson:"_id"`
Url string `bson:"url,omitempty" json:"url,omitempty"`
Identifier *Identifier `bson:"identifier,omitempty" json:"identifier,omitempty"`
Version string `bson:"version,omitempty" json:"version,omitempty"`
Name string `bson:"name,omitempty" json:"name,omitempty"`
Status string `bson:"status,omitempty" json:"status,omitempty"`
Experimental *bool `bson:"experimental,omitempty" json:"experimental,omitempty"`
Publisher string `bson:"publisher,omitempty" json:"publisher,omitempty"`
Contact []ValueSetContactComponent `bson:"contact,omitempty" json:"contact,omitempty"`
Date *FHIRDateTime `bson:"date,omitempty" json:"date,omitempty"`
LockedDate *FHIRDateTime `bson:"lockedDate,omitempty" json:"lockedDate,omitempty"`
Description string `bson:"description,omitempty" json:"description,omitempty"`
UseContext []CodeableConcept `bson:"useContext,omitempty" json:"useContext,omitempty"`
Immutable *bool `bson:"immutable,omitempty" json:"immutable,omitempty"`
Requirements string `bson:"requirements,omitempty" json:"requirements,omitempty"`
Copyright string `bson:"copyright,omitempty" json:"copyright,omitempty"`
Extensible *bool `bson:"extensible,omitempty" json:"extensible,omitempty"`
CodeSystem *ValueSetCodeSystemComponent `bson:"codeSystem,omitempty" json:"codeSystem,omitempty"`
Compose *ValueSetComposeComponent `bson:"compose,omitempty" json:"compose,omitempty"`
Expansion *ValueSetExpansionComponent `bson:"expansion,omitempty" json:"expansion,omitempty"`
}
which is part of a Go implementation of HL7 FHIR, including only the metadata fields, and omitting the three content three fields (codeSystem, compose and expansion). I can't (and shouldn't) change the JSON tags in the original source code, since other code strongly depends on it working the way it's written. How can I tell json.Marshal to override the existing JSON tags on these struct elements?
You can't change it, but you don't have to.
Easiest solution is to create your own struct, define your own json tags (how you want them to appear in the output), copy the fields, and marshal a value of your own struct.
E.g. let's say you want to marshal the Id and Urlfields, then:
type MyValueSet struct {
Id string `json:"MyId"`
Url string `json:"MyUrl"`
}
var vs ValueSet = ... // Comes from somewhere
mvs := MyValueSet {
Id: vs.Id,
Url: vs.Url,
}
data, err := json.Marshal(&mvs)
// Check err
I'm trying to pull reddit content from the json API into a custom structure for the client. the structure i've come up with in go for this is
type Subreddit struct {
offset int
num_of_posts int
subscribers: int
thumbnail string
children []post
}
type post struct {
type string
url string
thumbnail string
submitted_by string
upvotes int
downvotes int
}
unfortunately the reddit json isn't formatted even close to this and in addition i'll want to filter out url's i can't support etc.
The only way i know to do it this is to create an interface for each of the "children" in the source data, and iterate through each child manually, creating an individual "post" for each interface. and pushing them into the subreddit object's post array.
For reference the data is formatted like http://www.reddit.com/r/web_design/.json
Is this the right way to do this? Or is there a faster way. It seems like a lot of overhead for such a small task, but i'm a PHP Javascript dev, so It's just unusual for me I suppose.
Before I even start to answer the question:
Remember that your struct fields must be exported in order to be used with the encoding/json package.
Secondly I must admit I am not entirely sure what you meant with the entire create an interface for each of the "children" part. But it sounded complicated ;)
Anyway, to your answer:
If you wish to use the standard encoding/json package to unmarshal the json, you must use an intermediate structure unless you will use a similar structure as the one used by Reddit.
Below you can find an example of how parts of the Reddit structure might be mapped to Go structs. By Unmarshalling the json into an instance of RedditRoot, you can then easily iterate over the Children , remove any unwanted child, and populate your Subreddit struct:
type RedditRoot struct {
Kind string `json:"kind"`
Data RedditData `json:"data"`
}
type RedditData struct {
Children []RedditDataChild `json:"children"`
}
type RedditDataChild struct {
Kind string `json:"kind"`
Data *Post `json:"data"`
}
type Post struct {
Type string `json:"-"` // Is this equal to data.children[].data.kind?
Url string `json:"url"`
Thumbnail string `json:"thumbnail"`
Submitted_by string `json:"author"`
Upvotes int `json:"ups"`
Downvotes int `json:"downs"`
}