I am using Fiber package in Golang to handle the httprequests and want to find all the query params present in request
GET http://example.com/shoes?order=desc&brand=nike&lang=english
I want to iterate over query params and looking for something like this
for k, v := range c.AllQueries() {
reqObj[k] = v[0]
}
Expected output:
"order" : "desc"
"brand" : "nike"
"lang" : "english"
Here is the link of AllParams implementation. We can see this method returns a map[string]string of query params. So AllParams is what you need.
params := c.AllParams()
for k, v := range params {
// do something with the values
}
Edit:
Go-fiber uses fasthttp under the hood. You can look into this method block and iterate the fasthttp.QueryArgs() the way they are doing.
c.fasthttp.QueryArgs().VisitAll(func(key, val []byte) {
// implement what you want to do with the key values here
})
Related
I am implementing some DB logic without using an ORM.
Can I somehow create a mapping between struct keys and db enums?
type Message struct {
SomeKey string
SomeOtherKey string
}
MessageToDBEnum: = map[ ? MessageKey] string {
SomeKey: "some_key",
SomeOtherKey: "some_other_key"
}
can I later dynamically use the map key (eg when iterating throgh the map) to set/get struct values?
also can I somehow assure that MessageToDBEnum is exhaustive (all public keys of Message are included)?
You essentially want to convert a struct to map and vice versa. There are 3rd party libs to do that, e.g. github.com/mitchellh/mapstructure.
But we can do it ourselves too, it's not that hard. We may use reflection to do it. Without checking errors, here's the essence of the struct to map conversion:
func struct2Map(x interface{}) map[string]interface{} {
m := map[string]interface{}{}
v := reflect.ValueOf(x)
t := reflect.TypeOf(x)
for i := 0; i < v.NumField(); i++ {
m[t.Field(i).Name] = v.Field(i).Interface()
}
return m
}
You may use it like this:
msg := Message{
SomeKey: "v1",
SomeOtherKey: "v2",
}
m := struct2Map(msg)
fmt.Println(m)
Which outputs:
map[SomeKey:v1 SomeOtherKey:v2]
The backward conversion is even simpler, but know that for a function to modify a struct, you must pass a pointer to it. Again, without checking for possible errors, the essence of it is:
func map2Struct(m map[string]interface{}, d interface{}) {
s := reflect.ValueOf(d).Elem()
for k, v := range m {
s.FieldByName(k).Set(reflect.ValueOf(v))
}
}
Using it:
var msg2 Message
map2Struct(m, &msg2)
fmt.Printf("%+v\n", msg2)
Which outputs:
{SomeKey:v1 SomeOtherKey:v2}
Try the examples on the Go Playground.
You may build the validation into these conversion functions, and return an error or use default / zero values when an invalid value is found.
I've often encountered a situation where I have something like this:
type Article struct {
Title string
User string
Content []byte
Tags []string
}
Where I want to be able to perform query tasks like this:
var articles []Article
query := datastore.NewQuery("Article")
for _, filter := range filters {
if filter.User != "" {
query = query.Filter("User =", filter.User)
}
// how to do if for finding tags
}
keys, err := DatastoreClient().GetAll(ctx, query, &articles)
if err != nil {
return nil, err
}
return articles, nil
Let's say an article have the following tags []string{"golang", "ruby", "python", "programming"} and I want to retrieve all articles that contain the tags golang and programming, how could I efficiently achieve this?
Search in array in datastore with usage of equal sign works as contains.
https://cloud.google.com/datastore/docs/concepts/queries#properties_with_array_values_can_behave_in_surprising_ways
That means, that you need to make a query with two equal filters by this property.
Example on GQL.
SELECT * FROM Article WHERE Tags = "golang" AND Tags = "prgramming".
If Tags is an array, equal will behave as contains. That it. All the trick.
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
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!
I have a variable of type value that stores a map, but I can not access the values by providing the keys:
rascal>a
value: ("s":"s")
rascal>a["s"]
|stdin:///|(2,3,<1,2>,<1,5>): subscript not supported on value at |stdin:///|(2,3,<1,2>,<1,5>)
☞ Advice
How can I parse the value to map in order to be able to retrieve my value ?
if (map[str,str] myMap := a) {
// do stuff with myMap
}
else {
throw "<a> is not a map?";
}
Another way of "narrowing types" is using pattern matching in function parameters:
rascal>value x = 1;
int: 1
rascal>int myFunc(int i) = 2 * i;
ok
rascal>myFunc(x);
int: 2
And yet another way is using visit or switch:
visit(bigValue) {
case Expression e => ...work with e...
}
The general idea is:
pattern matching means narrowing (downcasting)
pattern matching may fail and so is always in a conditional context
there are many places in Rascal where you can use pattern matching: function dispatch, switch, visit, :=, <-
So I found some code that help me get started with reflection in Go (golang), but I'm having trouble getting a the underlying value so that I can basically create a map[string]string from a struct and it's fields.
Eventually, I'd like to make the result into a map[string]interface{}, but this one issue is kind of blocking me.
The code I have at the moment:
package main
import (
"fmt"
"reflect"
)
type Foo struct {
FirstName string `tag_name:"tag 1"`
LastName string `tag_name:"tag 2"`
Age int `tag_name:"tag 3"`
}
func inspect(f interface{}) map[string]string {
m := make(map[string]string)
val := reflect.ValueOf(f).Elem()
for i := 0; i < val.NumField(); i++ {
valueField := val.Field(i)
typeField := val.Type().Field(i)
f := valueField.Interface()
val := reflect.ValueOf(f)
m[typeField.Name] = val.String()
}
return m
}
func dump(m map[string]string) {
for k, v := range m {
fmt.Printf("%s : %s\n", k, v)
}
}
func main() {
f := &Foo{
FirstName: "Drew",
LastName: "Olson",
Age: 30,
}
a := inspect(f)
dump(a)
}
The output from running the code:
FirstName : Drew
LastName : Olson
Age : <int Value>
From what I understand the output for FirstName and LastName are actual reflect.Value objects but for strings the String() method on value just outputs the underlying String. I'd like to either get the int and change it into a string, but from the relfect package documentation I'm not immediately seeing how that's done.
Soo.... How do I get the underlying value from a reflect.Value in golang?
A good example of how to parse values is the fmt package. See this code.
Using the mentioned code to match your problem would look like this:
switch val.Kind() {
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
m[typeField.Name] = strconv.FormatInt(val.Int(), 10)
case reflect.String:
m[typeField.Name] = val.String()
// etc...
}
Basically you need to check for all available Kinds.
It looks like you're on the right track. The problem I see with your code is it makes assumptions about the values, meaning when do you call Elem() and how many times (to resolve pointers). In order to know this you need to look at the reflect.Kind. Is the value a reflect.Ptr? Then use Elem().
Once you have the value from val.Interface() / val.String() / val.Int() you can convert your values as needed. What you use is going to depend on reflect.Kind. To convert an int to/from string you need to use the strconv package.
The encoding/json and encoding/xml packages do this kind of work already. The source code provides some great examples. For example, take a look at copyValue in encoding/xml/read.go and marshalSimple in encoding/xml/marshal.go.
This should be easier to do with Go 1.5 (August 2015)
See review 8731 and commit 049b89d by Rob Pike (robpike):
fmt: treat reflect.Value specially - as the value it holds
This would allow you to print the actual value of a Reflect.Value() argument:
When a reflect.Value is passed to Printf (etc.), fmt called the String method, which does not disclose its contents.
To get the contents, one could call Value.Interface(), but that is illegal
if the Value is not exported or otherwise forbidden.
This CL improves the situation with a trivial change to the fmt package: when we see a reflect.Value as an argument, we treat it exactly as we treat a reflect.Value we make inside the package.
This means that we always print the contents of the Value as if that was the argument to Printf.
This is arguably a breaking change but I think it is a genuine improvement and no greater a break than many other tweaks we have made to formatted output from this package.
Another simple solution can be ,
flavorName = fmt.Sprintf("%v",strct)
" fmt.Sprintf() " will return the value which can be stored in a variable.