Converting map to struct

Question

I am trying to create a generic method in Go that will fill a struct using data from a map string interface    For example  the method signature and usage might look like   func FillStruct data map string interface    result interface                 type MyStruct struct       Name string     Age  int64    myData    make map string interface    myData  Name      Tony  myData  Age      23  result     amp MyStruct   FillStruct myData  result      result now has Name set to  Tony  and Age set to 23   I know this can be done using JSON as an intermediary  is there another more efficient way of doing this

User · Answer

There are two steps   Convert interface to JSON Byte Convert JSON Byte to struct  Below is an example  dbByte       json Marshal dbContent      json Unmarshal dbByte   amp MyStruct

User · Answer

the simplest way to do that is using encoding json package   just for example   package main import        fmt       encoding json     type MyAddress struct       House string     School string   type Student struct       Id int64     Name string     Scores float32     Address MyAddress     Labels   string    func Test          dict    make map string interface        dict  id     201902181425          int     dict  name      jackytse           string     dict  scores     123 456           float     dict  address     map string string  house   my house    school   my school        map     dict  labels       string  aries    warmhearted    frank           slice      jsonbody  err    json Marshal dict      if err    nil              do error check         fmt Println err          return            student    Student       if err    json Unmarshal jsonbody   amp student   err    nil              do error check         fmt Println err          return            fmt Printf    v n   student     func main         Test

User · Answer

You can do it     it may get a bit ugly and you ll be faced with some trial and error in terms of mapping types    but heres the basic gist of it   func FillStruct data map string interface    result interface          t    reflect ValueOf result  Elem       for k  v    range data           val    t FieldByName k          val Set reflect ValueOf v             Working sample  http   play golang org p PYHz63sbvL

User · Answer

I adapt dave s answer  and add a recursive feature  I m still working on a more user friendly version  For example  a number string in the map should be able to be converted to int in the struct   package main  import        fmt       reflect     func SetField obj interface    name string  value interface    error        structValue    reflect ValueOf obj  Elem       fieldVal    structValue FieldByName name       if  fieldVal IsValid             return fmt Errorf  No such field   s in obj   name             if  fieldVal CanSet             return fmt Errorf  Cannot set  s field value   name             val    reflect ValueOf value       if fieldVal Type      val Type              if m ok    value  map string interface     ok                   if field value is struct             if fieldVal Kind      reflect Struct                   return FillStruct m  fieldVal Addr   Interface                                  if field value is a pointer to struct             if fieldVal Kind    reflect Ptr  amp  amp  fieldVal Type   Elem   Kind      reflect Struct                   if fieldVal IsNil                         fieldVal Set reflect New fieldVal Type   Elem                                          fmt Printf  recursive   v  v n   m fieldVal Interface                    return FillStruct m  fieldVal Interface                                      return fmt Errorf  Provided value type didn t match obj field type              fieldVal Set val      return nil     func FillStruct m map string interface    s interface    error       for k  v    range m           err    SetField s  k  v          if err    nil               return err                     return nil    type OtherStruct struct       Name string     Age  int64     type MyStruct struct       Name string     Age  int64     OtherStruct  OtherStruct      func main         myData    make map string interface        myData  Name             Tony      myData  Age             int64 23      OtherStruct    make map string interface        myData  OtherStruct     OtherStruct     OtherStruct  Name        roxma      OtherStruct  Age        int64 23       result     amp MyStruct       err    FillStruct myData result      fmt Println err      fmt Printf   v  v n  result result OtherStruct

User · Answer

Hashicorp s https   github com mitchellh mapstructure library does this out of the box   import  github com mitchellh mapstructure   mapstructure Decode myData   amp result    The second result parameter has to be an address of the struct

User · Answer

The simplest way would be to use https   github com mitchellh mapstructure   import  github com mitchellh mapstructure   mapstructure Decode myData   amp result    If you want to do it yourself  you could do something like this   http   play golang org p tN8mxT V9h  func SetField obj interface    name string  value interface    error       structValue    reflect ValueOf obj  Elem       structFieldValue    structValue FieldByName name       if  structFieldValue IsValid             return fmt Errorf  No such field   s in obj   name             if  structFieldValue CanSet             return fmt Errorf  Cannot set  s field value   name             structFieldType    structFieldValue Type       val    reflect ValueOf value      if structFieldType    val Type             return errors New  Provided value type didn t match obj field type              structFieldValue Set val      return nil    type MyStruct struct       Name string     Age  int64    func  s  MyStruct  FillStruct m map string interface    error       for k  v    range m           err    SetField s  k  v          if err    nil               return err                     return nil    func main         myData    make map string interface        myData  Name      Tony      myData  Age     int64 23       result     amp MyStruct       err    result FillStruct myData      if err    nil           fmt Println err            fmt Println result

[go] Converting map to struct

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