Go: reflect : Call with too few input arguments - reflection

Question

I've stucked with problems of using reflect library. I descided to use it because of many recomendations, but i'm just learning go and some parts are not really easy..
I've got this part of code :
func countDataByName(sourceName string, statData interface{}, filters Filter, chartName string) []ChartElement {
...
//step 1 - filter
filteredData := reflect.ValueOf(statData).MethodByName("FilterData").Call([]reflect.Value{})
//step 2 - cluster
// clusterData := reflect.ValueOf(filteredData).MethodByName("clusterData").Call([]reflect.Value{})
//step 3 - count
// countedData := reflect.ValueOf(clusterData).MethodByName(chartName).Call([]reflect.Value{})
fmt.Println("Never prints to anywhere", filteredData)
...
return filterData
}
If I execute the method like this, I get error : reflect: Call with too few input arguments. But if I change reflect.ValueOf(statData) on reflect.ValueOf(&statData) than error is reflect: call of reflect.Value.Call on zero Value
statData comes with one of 2 types, and fore this types I have structs and methods, like this :
type NoaggModel struct {
Date string
Hour int
Id_user int
Id_line int
Id_region int
Id_tree_devision int
N_inb int
N_inb_d int
T_ring int
T_inb int
T_inb_d int
T_hold int
T_acw int
T_acw_d int
T_wait int
}
func (ng *NoaggModel) FilterData( data NoaggModel) {
fmt.Println("FilterData")
fmt.Println("data : ", data)
}
this Println also not works. Code panics above , and method was not triggered. Where is my mistake here?
Upd 1:
Found that if I remove param data in functioin that I want to call, than it calls nicely. But!
I have statData as 1 row, of structs, so type is NoaggModel. And in the method FilterData I get this 1 row as ng. But I need to change it to the []NoaggModel. How to call reflect in this case and how to pass parameter to the filter function ?
Upd 2:
I modified few parts :
func (ng *NoaggModel) FilterData(filter interface{}, data NoaggModel) {
fmt.Println("data : ",ng)
}
In here, how to pass correct type to filter, if it is set up in revel controller, and method is in model. Or should I set the type in each model and call it in controller?
And in controller I wrote :
//step 1 - filter
in := make([]reflect.Value, 2)
in[0] = reflect.ValueOf(filters)
in[1] = reflect.ValueOf(statData)
filteredData := reflect.ValueOf(statData).MethodByName("FilterData").Call(in)
StatData is a row of type NoaggModel, but I get the error :
reflect: Call using *models.NoaggModel as type models.NoaggModel
The type was set also by reflect in code above, like this :
...
var sourceTypes = map[string]reflect.Type{
"noagg": reflect.TypeOf(models.NoaggModel{}),
"oracle": reflect.TypeOf(models.OracleModel{}),
}
deserializedData = reflect.New(sourceTypes[sourceName]).Interface()
...
// deserialised becomes statData

Answer 1

Reflection is not easy. And should be avoided if possible.
I admit that I did recommend using reflect to dynamically create instances of types based on a map, which is really useful when you don't know which types you might have to handle. But in your case you should consider using interfaces.
While I don't really know what you want to achieve, I would suggest starting by creating an interface that all your Models need to implement (modify it to fit your needs):
type Model interface {
FilterData(interface{})
}
NoaggModel and OracleModel would then implement the above interface by defining similar methods like this:
func (ng *NoaggModel) FilterData(filter interface{}) {
fmt.Printf("data: %#v, filter: %#v\n", ng, filter)
}
Then, change deserializedData (and statData) to be of the interface type Model instead of interface{}. And since you only have two types, you can avoid using reflect by having a switch instead:
...
var deserializedData Model
switch sourceName {
case "noagg":
deserializedData = new(models.NoaggModel)
case "oracle":
deserializedData = new(models.OracleModel)
}
...
// Marshal the values into deserializedData which now holds an instance of the desired type
...
deserializedData.FilterData("Replace this string with your filter")
And it is done without having to import reflect!