cocoonspace · jfbus · Jul 24, 2020 · Jul 24, 2020 · Jul 24, 2020 · Jul 24, 2020
diff --git a/README.md b/README.md
@@ -18,6 +18,9 @@ GET https://api.example.com/v1/foos/1?select=foo
 {"foo":1}
 ```
 
+dynjson mimicks the original struct using the original types and json tags.
+The field order is the same as the select parameters.
+
 ## Installation
 
 go get github.com/cocoonspace/dynjson
@@ -33,13 +36,37 @@ type APIResult struct {
 f := dynjson.NewFormatter()
 
 res := &APIResult{Foo:1, Bar:"bar"}
-o, err := f.Format(res, []string{"foo"}, nil)
+o, err := f.Format(res, dynjson.FieldsFromRequest(r))
 if err != nil {
     // handle error
 }
 err := json.Marshal(w, o) // {"foo": 1}
 ```
 
+With struct fields :
+
+
+```go
+type APIResult struct {
+    Foo int          `json:"foo"`
+    Bar APIIncluded  `json:"bar"`
+}
+
+type APIIncluded struct {
+    BarFoo int    `json:"barfoo"`
+    BarBar string `json:"barbar"`
+}
+
+f := dynjson.NewFormatter()
+
+res := &APIResult{Foo: 1, Bar: APIIncluded{BarFoo:1, BarBar: "bar"}}
+o, err := f.Format(res, []string{"foo", "bar.barfoo"})
+if err != nil {
+    // handle error
+}
+err := json.Marshal(w, o) // {"foo": 1, "bar":{"barfoo": 1}}
+```
+
 With slices:
 
 ```go
@@ -50,8 +77,8 @@ type APIResult struct {
 
 f := dynjson.NewFormatter()
 
-res := []APIResult{{Foo:1, Bar:"bar"}}
-o, err := f.Format(res, []string{"foo"}, nil)
+res := []APIResult{{Foo: 1, Bar: "bar"}}
+o, err := f.Format(res, []string{"foo"})
 if err != nil {
     // handle error
 }
@@ -72,8 +99,8 @@ type APIItem struct {
 
 f := dynjson.NewFormatter()
 
-res := &APIResult{Foo:1, Bar:[]APIItem{{BarFoo:1, BarBar: "bar"}}}
-o, err := f.Format(res, []string{"foo", "bar.barfoo"}, nil)
+res := &APIResult{Foo: 1, Bar: []APIItem{{BarFoo: 1, BarBar: "bar"}}}
+o, err := f.Format(res, []string{"foo", "bar.barfoo"})
 if err != nil {
     // handle error
 }

diff --git a/request.go b/request.go
@@ -0,0 +1,30 @@
+package dynjson
+
+import (
+	"net/http"
+	"net/url"
+	"strings"
+)
+
+type Option int
+
+const (
+	OptionMultipleFields Option = iota
+	OptionCommaList
+)
+
+// FieldsFromRequest returns the list of fields requested from a http.Request
+// Without opt or with OptionMultipleFields, the expected format is:
+// http://api.example.com/endpoint?select=foo&select=bar
+// With OptionCommaList, the expected format is:
+// http://api.example.com/endpoint?select=foo,bar
+func FieldsFromRequest(r *http.Request, opt ...Option) []string {
+	vals, err := url.ParseQuery(r.URL.RawQuery)
+	if err != nil {
+		return nil
+	}
+	if len(opt) == 1 && opt[0] == OptionCommaList && len(vals["select"]) > 0 {
+		return strings.Split(vals["select"][0], ",")
+	}
+	return vals["select"]
+}
diff --git a/request_test.go b/request_test.go
@@ -0,0 +1,49 @@
+package dynjson
+
+import (
+	"net/http"
+	"testing"
+)
+
+func TestFieldsFromRequest(t *testing.T) {
+	{
+		r, err := http.NewRequest(http.MethodGet, "http://api.example.com/endpoint?select=foo&select=bar", nil)
+		if err != nil {
+			t.Error("Should not have returned", err)
+		}
+		fields := FieldsFromRequest(r)
+		if len(fields) != 2 {
+			t.Error("2 fields were expected")
+		}
+		if fields[0] != "foo" || fields[1] != "bar" {
+			t.Errorf("Expected [foo bar] but got %v", fields)
+		}
+	}
+	{
+		r, err := http.NewRequest(http.MethodGet, "http://api.example.com/endpoint?select=foo&select=bar", nil)
+		if err != nil {
+			t.Error("Should not have returned", err)
+		}
+		fields := FieldsFromRequest(r, OptionMultipleFields)
+		if len(fields) != 2 {
+			t.Error("2 fields were expected")
+		}
+		if fields[0] != "foo" || fields[1] != "bar" {
+			t.Errorf("Expected [foo bar] but got %v", fields)
+		}
+	}
+	{
+		r, err := http.NewRequest(http.MethodGet, "http://api.example.com/endpoint?select=foo,bar", nil)
+		if err != nil {
+			t.Error("Should not have returned", err)
+		}
+		fields := FieldsFromRequest(r, OptionCommaList)
+		if len(fields) != 2 {
+			t.Error("2 fields were expected")
+		}
+		if fields[0] != "foo" || fields[1] != "bar" {
+			t.Errorf("Expected [foo bar] but got %v", fields)
+		}
+	}
+
+}