I have the following response struct that I want to use as a base wrapper for responding to API calls users send to me.
type Response struct {
Data ??? `json:"data,omitempty"`
Time int64 `json:"time,omitempty"`
Message string `json:"message,omitempty"`
}
The type of the Data field is varying and could be a map[string]*CustomStruct1 map[string*CustomStruct2 or an []CustomStruct3.
What is the best way to attack this kind of problem?
One option is to simply treat "Data" as the interface{} (any) type, instead of using your custom structs, and handle the resulting values based on inspection of what actually got unmarshaled. Of course, once you've inspected the data to determine what type it should be you could convert it into the appropriate strong type after the fact.
type Response struct {
Data interface{} `json:"data,omitempty"`
Time int64 `json:"time,omitempty"`
Message string `json:"message,omitempty"`
}
Another option is to embed the "Response" struct into specialized structs that look for your custom types and unmarshal into the appropriate one, assuming you know which one you've got ahead of time:
type BaseResponse struct {
Time int64 `json:"time,omitempty"`
Message string `json:"message,omitempty"`
}
type Response1 struct {
BaseResponse
Data map[string]*CustomStruct1 `json:"data"`
}
type Response2 struct {
BaseResponse
Data map[string]*CustomStruct2 `json:"data"`
}
// etc...
Ultimately, the unmarshaler cannot pick a varying type based on the document that gets unmarshaled, it only deserializes JSON values into structures either defined explicitly by you or into generic ones.
You could try to use reflection, but it wouldn't be very idiomatic.
Related
I need to marshal into this JSON format:
{"messageProtocolHandshake":[{"handshakeType":"announceMax"},{"version":[{"major":1},{"minor":0}]}]}
Problem is matching the handshakeType. My struct is
type MessageProtocolHandshake struct {
HandshakeType HandshakeType `json:"handshakeType"`
Version []Version `json:"version"`
}
type HandshakeType struct {
HandshakeType string
}
Marshaling can be done using slice of interface:
func (h MessageProtocolHandshake) MarshalJSON() ([]byte, error) {
res := make([]interface{}, 3)
res[0] = struct {
HandshakeType string `json:"handshakeType"`
}{h.HandshakeType.HandshakeType}
res[1] = struct {
Version []Version `json:"version"`
}{h.Version}
return json.Marshal(res)
}
Using a simple marshaler/unmarshaler takes away the surrounding curly brackets from the handshakeType, so that doesn't work:
{"messageProtocolHandshake":[{"handshakeType":"announceMax","version":[{"major":1,"minor":0}],"formats":[{"format":"JSON-UTF8"}]}]}
Seems as if Go applies some heuristic in that case on the retuned byte array (undocumented?).
Is there a more elegant way of omitting the structs outer field name?
--
UPDATE To summarise the answers: key is to think about different structs for marshalling and unmarshalling if nothing else works, potentially a using a 3rd presentation for working internally with the data.
When custom (Un)Marshalers come into play remember that promoted fields inherit their methods and hence influence parent structs.
The JSON that you specified has a different model from that of your struct.
There are a few approaches to aligning these: Change the specification of the JSON data to match your structs, change the structs to match the specification of the JSON, or create a new struct that is only used for marshaling.
I omit the last example, because it's very similar to the second method.
Changing the specification of the JSON
The following model stays the same:
type MessageProtocolHandshake struct {
HandshakeType HandshakeType `json:"handshakeType"`
Version []Version `json:"version"`
}
type HandshakeType struct {
HandshakeType string
}
The JSON for this would be:
{"handshakeType":{"HandshakeType":""},"version":[]}
You did not specify the Version type so I don't know how one would change the JSON for that.
Changing the structs
The following JSON stays the same:
{"messageProtocolHandshake":[{"handshakeType":"announceMax"},{"version":[{"major":1},{"minor":0}]}]}
The structs for this would be:
type Model struct {
MessageProtocolHandshake []interface{} `json:"messageProtocolHandshake"`
}
type HandshakeType struct {
HandshakeType string `json:"handshakeType"`
}
type Versions struct {
Version []Version `json:"version"`
}
type Version struct {
Major *int `json:"major,omitempty"`
Minor *int `json:"minor,omitempty"`
}
Unmarshaling would not be trivial.
https://play.golang.org/p/89WUhcMFM0B
As is obvious from the results, the models you are using are not good. If there's a way to change all of this, I would recommend starting from scratch, using the data that is necessary and creating the JSON specification from the structs.
I recommend reading up on JSON: https://www.json.org/json-en.html
Also, I recommend this introduction to Go and JSON: https://blog.golang.org/json
I'm trying to parse some xml documents in Go. I need to define a few structs for this purpose, and my struct tags depend on a certain condition.
Imagine the following code (even though I know it won't work)
if someCondition {
type MyType struct {
// some common fields
Date []string `xml:"value"`
}
} else {
type MyType struct {
// some common fields
Date []string `xml:"anotherValue"`
}
}
var t MyType
// do the unmarshalling ...
The problem is that these two structs have lots of fields in common. The only difference is in one of the fields and I want to prevent duplication. How can I solve this problem?
You use different types to unmarshal. Basically, you write the unmarshaling code twice and either run the first version or the second. There is no dynamic solution to this.
The simplest is probably to handle all possible fields and do some post-processing.
For example:
type MyType struct {
DateField1 []string `xml:"value"`
DateField2 []string `xml:"anotherValue"`
}
// After parsing, you have two options:
// Option 1: re-assign one field onto another:
if !someCondition {
parsed.DateField1 = parsed.DateField2
parsed.DateField2 = nil
}
// Option 2: use the above as an intermediate struct, the final being:
type MyFinalType struct {
Date []string `xml:"value"`
}
if someCondition {
final.Date = parsed.DateField1
} else {
final.Date = parsed.DateField2
}
Note: if the messages are sufficiently different, you probably want completely different types for parsing. The post-processing can generate the final struct from either.
As already indicated, you must duplicate the field. The question is where the duplication should exist.
If it's just a single field of many, one option is to use embedding, and field shadowing:
type MyType struct {
Date []string `xml:"value"`
// many other fields
}
Then when Date uses the other field name:
type MyOtherType struct {
MyType // Embed the original type for all other fields
Date []string `xml:"anotherValue"`
}
Then after unmarshaling of MyOtherType, it's easy to move the Date value into the original struct:
type data MyOtherType
err := json.Unmarshal(..., &data)
data.MyType.Date = data.Date
return data.MyType // will of MyType, and fully populated
Note that this only works for unmarshaling. If you need to also marshal this data, a similar trick can be used, but the mechanics around it must be essentially reversed.
I have big structure with more than 50 params
type Application struct {
Id int64 `json:"id"`
FullName string `json:"fullName,omitempty"`
ActualAddress string `json:"actualAddress,omitempty"`
.....
}
I use gin-gonic and when I return application I need to omit some params I've created a function which makes empty some params (playLink) and then gin returns me correct json (without unnecessary values). I heard that reflection isn't fast operation so in our case we can use a lot of ugly if-else or switch-cases. Is there any other solutions faster than reflecting and more beautiful than if-elses?
The thing is that structure params have non-empty values, so they wont by omitted by gin. That's why I've created function to make some params empty before return
The thing is, if you only want to zero a few fields, it's more readable to do it without a function, e.g.
app := Application{}
app.FullName, app.ActualAddress = "", ""
If you want to create a function for it, at least use variadic parameter, so it's easier to call it:
func zeroFields(application *Application, fields ...string) {
// ...
}
So then calling it:
zeroFields(&app, "FullName", "ActualAddress")
Yes, this will have to use reflection, so it's slower than it could be, and error prone (mistyped names can only be detected at runtime). If you want to avoid using reflection, pass the address of the fields:
func zeroFields(ps ...*string) {
for _, p := range ps {
*p = ""
}
}
This way you have compile-time guarantee that you type field names correctly, and that they have string type.
Calling it:
zeroFields(&application.FullName, &application.ActualAddress)
Try it on the Go Playground.
If I understand correctly: you want to return some values from your struct but not all of them? Perhaps a nested struct?
type Application struct {
ID struct {
ID int64 `json:"id"`
} `json:"id"`
Person struct {
Fullname string `json:"Fullname"
} `json:"person"
}
That should let you filter out the fields you want to use.
I'm new to Go and working with a set of types generated by gowsdl based on the NetSuite SuiteTalk web service definition. It has created the following types:
type BaseRef struct {
XMLName xml.Name `xml:"urn:core_2018_2.platform.webservices.netsuite.com BaseRef"`
Name string `xml:"name,omitempty"`
}
type RecordRef struct {
XMLName xml.Name `xml:"urn:core_2018_2.platform.webservices.netsuite.com RecordRef"`
*BaseRef
InternalId string `xml:"internalId,attr,omitempty"`
ExternalId string `xml:"externalId,attr,omitempty"`
Type *RecordType `xml:"type,attr,omitempty"`
}
type GetRequest struct {
XMLName xml.Name `xml:"urn:messages_2018_2.platform.webservices.netsuite.com GetRequest"`
BaseRef *BaseRef `xml:"baseRef,omitempty"`
}
As I try to use these types it is unhappy in my ability to use the specific type of reference record in a GetRequest structure which is looking for a BaseRef which is what RecordRef is based on.
var partnerRecordType RecordType
partnerRecordType = RecordTypePartner
recordRef := RecordRef{
Type:&partnerRecordType,
InternalId:internalIdString,
}
var getRequest GetRequest
getRequest.BaseRef = &recordRef
The error I get is on the last line is:
cannot use &recordRef (type *RecordRef) as type *BaseRef in assignment
Any thoughts on how to proceed?
Go does not support polymorphism in this way, neither does it support inheritance in way that say C# or Java does. Embedded structs are quite literally just embedded, they do not create a classical inheritance hierarchy. They simply give the wrapping struct all of the exposed methods and fields of the embedded struct (with some subtle caveats - check out the spec)
That said, in your example RecordRef is not related to BaseRef in terms of its type, instead it could be considered to "contain" a pointer to a BaseRef. In order for your program to compile, you will have explicitly assign the embedded BaseRef like so:
getRequest.BaseRef = &recordRef.BaseRef
As this code you are referencing has been auto generated from a WSDL, it may be a little cumbersome to update the GetRequest to provide a BaseRef like data structure in a more polymorphic, flexible fashion, but in order to do so you will need to use Go interfaces.
You could update the GetRequest to have a method with accepts in interface type, say XmlRef which would expose getters that can derive the data you need to assign to the GetRequest
For example
type XmlRef interface {
Name() string
InternalID() string
ExternalID() string
}
func (r *GetRequest) SetRef(ref XmlRef) {
r.BaseRef.Name = ref.Name()
// etc...
}
Then simply implement the interface for RecordRef and any other structs that would need to be used in this context.
If I understand you right, you are looking for a method to access a struct's embbed field. You can simply use recordRef.BaseRef for that purpose.
Further reading: https://golang.org/ref/spec#Struct_types
It is possible to connect to netsuite with the output of go2wsdl but many tweaks are required. A full proof of concept is available here:
https://github.com/mk-j/go-netsuite-soap
But here are some examples of some of the tweaks required:
sed -i 's/urn:.*1.lists.webservices.netsuite.com //' netsuite.go
Tweaking BaseRef and GetRequest:
type BaseRef struct {
Name string `xml:"name,omitempty" json:"name,omitempty"`
InternalId string `xml:"internalId,attr,omitempty" json:"internalId,omitempty"`
ExternalId string `xml:"externalId,attr,omitempty" json:"externalId,omitempty"`
Type *RecordType `xml:"type,attr,omitempty" json:"type,omitempty"`
XsiType string `xml:"xsi:type,attr,omitempty"`
}
type GetRequest struct {
XMLName xml.Name `xml:"get"`
XmlNSXSI string `xml:"xmlns:xsi,attr"`
XmlNSPC string `xml:"xmlns:platformCore,attr"`
BaseRef *BaseRef `xml:"baseRef,omitempty" json:"baseRef,omitempty"`
}
Then this code produced an successful xml response from the soap server:
recordType := netsuite.RecordTypePartner
baseRef :=netsuite.BaseRef{
InternalId:"1234",
Type:&recordType,
XsiType:"platformCore:RecordRef",
}
request := netsuite.GetRequest{
BaseRef:&baseRef,
XmlNSXSI: "http://www.w3.org/2001/XMLSchema-instance",
XmlNSPC:"urn:core_2022_1.platform.webservices.netsuite.com",
}
getResponse, err := service.Get(&request)
Which made the raw request:
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Header><tokenPassport>[redacted]</tokenPassport></soap:Header>
<soap:Body>
<get xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:platformCore="urn:core_2022_1.platform.webservices.netsuite.com">
<baseRef internalId="1234" type="partner" xsi:type="platformCore:RecordRef"></baseRef>
</get>
</soap:Body>
</soap:Envelope>
Sources used: https://www.zuar.com/blog/netsuite-api-exploring-soap/
This question is best described by an example
http://play.golang.org/p/bQuRr0kV-b
I am trying to make a composable struct. In this example, I want to have a Person type with embedded values from either Female or Male. If I were just dealing with structs, I would embed them like this
type Person Struct{
Female
Male
}
I cannot do this however, both because in the actual project, there are a lot of embedded structs and I would prefer to keep the struct clean and composable. But there is also a naming conflict — in this example, both Male and Female contain the field 'Eyes'. Moving the conflicting value to the Person struct is not a viable solution (as many of the other embedded structs do not contain that particular value).
I was hoping to pass these values via a simple interface. Sample Below: When running this code, I get &{Name: Age:0 Type:male GenderType:0x10434120} where GenderType is the pointer to Male struct(in this case). My Goal is to have a flat structure returned that would look like &{Name: Age:0 Type:male Eyes: ChestSize:0}
package main
import "fmt"
type Person struct {
Name string
Age int
Type string
GenderType
}
type GenderType interface {
TypeName() string
}
type Male struct {
Eyes string
ChestSize int
}
type Female struct {
Eyes string
BustSize int
}
func (m *Male) TypeName() string {
return "male"
}
func (f *Female) TypeName() string {
return "female"
}
func main() {
d := NewHuman(new(Male))
fmt.Printf("%+v", d)
}
func NewHuman(gt GenderType) *Person {
return &Person{
Type: gt.TypeName(),
GenderType: gt,
}
}
I don't think it is possible to do this in a flat structure because it would entail changing the memory structure of the struct type during runtime, which go doesn't allow. While you can access embedded fields using GenderType, it's still allowed because you are saying that this will be a reference to an embedded struct that satisfies the interface rather than changing the structure of the struct itself.
I think the better way to marshal into a flat json using this is to keep your embedded structure, but then make the Person struct a Marshaler
You can add your own custom MarshalJSON() (byte[],error) method and use this to make a flat json output.
If you need specialized unmarshaling, then you can do likewise with an (UnmarshalJSON([]byte) error) method tied to Person.
see https://golang.org/pkg/encoding/json/#Marshaler for further reference
Here is a playground that shows what I mean: https://play.golang.org/p/qOl9WSaI3O