Unmarshaling nested JSON objects

Question

There are a few questions on the topic but none of them seem to cover my case  thus I m creating a new one   I have JSON like the following     foo     bar    1    baz    2      more    text     Is there a way to unmarshal the nested bar property and assign it directly to a struct property without creating a nested struct   The solution I m adopting right now is the following   type Foo struct       More String  json  more       Foo  struct           Bar string  json  bar           Baz string  json  baz          json  foo           FooBar  string  json  foo bar       This is a simplified version  please ignore the verbosity  As you can see  I d like to be able to parse and assign the value to      FooBar  string  json  foo bar     I ve seen people using a map  but that s not my case  I basically don t care about the content of foo  which is a large object   except for a few specific elements   What is the correct approach in this case  I m not looking for weird hacks  thus if this is the way to go  I m fine with that

User · Answer

Like what Volker mentioned  nested structs is the way to go  But if you really do not want nested structs  you can override the UnmarshalJSON func    https   play golang org p dqn5UdqFfJt  type A struct       FooBar string    takes foo bar     FooBaz string    takes foo baz     More   string     func  a  A  UnmarshalJSON b   byte  error        var f interface       json Unmarshal b   amp f       m    f  map string interface         foomap    m  foo       v    foomap  map string interface         a FooBar   v  bar    string      a FooBaz   v  baz    string      a More   m  more    string       return nil     Please ignore the fact that I m not returning a proper error   I left that out for simplicity     UPDATE  Correctly retrieving  more  value

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Is there a way to unmarshal the nested bar property and assign it directly to a struct property without creating a nested struct    No  encoding json cannot do the trick with   some deep childnode  like encoding xml can do  Nested structs is the way to go

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Combining map and struct allow unmarshaling nested JSON objects where the key is dynamic     map string   For example  stock json       MU          symbol    MU        title    micro semiconductor        share   400       purchase price   60 5       target price   70         LSCC         symbol    LSCC        title    lattice semiconductor        share   200       purchase price   20       target price   30         Go application  package main  import        encoding json       fmt       io ioutil       log       os     type Stock struct       Symbol        string   json  symbol       Title         string   json  title       Share         int      json  share       PurchasePrice float64  json  purchase price       TargetPrice   float64  json  target price     type Account map string Stock  func main         raw  err    ioutil ReadFile  stock json       if err    nil           fmt Println err Error            os Exit 1            var account Account     log Println account      The dynamic key in the hash is handle a string  and the nested object is represented by a struct

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Assign the values of nested json to struct until you know the underlying type of json keys -   package main  import        encoding json       fmt        Object type Object struct       Foo map string map string string  json  foo       More string  json  more      func main        someJSONString      byte    foo     bar    1    baz    2      more    text         var obj Object     err    json Unmarshal someJSONString   amp obj      if err    nil          fmt Println err            fmt Println  jsonObj   obj

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This is an example of how to unmarshall JSON responses from the Safebrowsing v4 API sbserver proxy server   https   play golang org p 4rGB5da0Lt     this example shows how to unmarshall JSON requests from the Safebrowsing v4 sbserver package main  import        fmt       log       encoding json        response from sbserver POST request type Results struct       Matches   Match            nested within sbserver response type Match struct       ThreatType string      PlatformType string      ThreatEntryType string      Threat struct           URL string          func main         fmt Println  Hello  playground           sample POST request          curl -X POST -H  Content-Type  application json          -d    threatInfo     threatEntries      url    http   testsafebrowsing appspot com apiv4 ANY PLATFORM MALWARE URL                http   127 0 0 1 8080 v4 threatMatches find         sample JSON response     jsonResponse       matches     threatType   MALWARE   platformType   ANY PLATFORM   threatEntryType   URL   threat    url   http   testsafebrowsing appspot com apiv4 ANY PLATFORM MALWARE URL             res     amp Results       err    json Unmarshal   byte jsonResponse   res          if err  nil                log Fatal err                 fmt Printf   v n  res      fmt Printf   tThreat Type   s n  res Matches 0  ThreatType      fmt Printf   tPlatform Type   s n  res Matches 0  PlatformType      fmt Printf   tThreat Entry Type   s n  res Matches 0  ThreatEntryType      fmt Printf   tURL   s n  res Matches 0  Threat URL

User · Answer

Yes  With gjson all you have to do now is   bar    gjson Get json   foo bar    bar could be a struct property if you like  Also  no maps

User · Answer

What about anonymous fields  I m not sure if that will constitute a  nested struct  but it s cleaner than having a nested struct declaration  What if you want to reuse the nested element elsewhere   type NestedElement struct      someNumber int  json  number       someString string  json  string      type BaseElement struct       NestedElement  json  bar

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I was working on something like this  But is working only with structures generated from proto  https   github com flowup-labs grpc-utils  in your proto     message Msg     Firstname string   1   gogoproto jsontag     name firstname      PseudoFirstname string   2   gogoproto jsontag     lastname      EmbedMsg   3    gogoproto nullable    false   gogoproto embed    true     Lastname string   4   gogoproto jsontag     name lastname      Inside string    5   gogoproto jsontag     name inside a b c       message EmbedMsg     Opt1 string   1   gogoproto jsontag     opt1        Then your output will be        lastname    Three    name          firstname    One        inside              a                  b                      c    goo                                      lastname    Two      opt1    var

[json] Unmarshaling nested JSON objects

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