Merge pull request #11 from dumim/develop

Omitempty implemented with intelligent default value checks

Author: dumim

README.md

@@ -118,6 +118,8 @@ whereas using `bar` (`ToMap(obj, "bar")`) on the same `obj` will result in:
 - Dot notation will create a parent-child relationship for every `.`.
 - Not setting any tag will ignore that field, unless if it's a struct; then it will go inside the struct to check its tags
 - `-` will explicitly ignore that field. As opposed to above, it will not look inside even if the field is of struct type.
+- `,omitempty` can be used similar to the `json` package to skip fields that have empty values
+  - this also handles default empty values (`""` for `string`, `0` for `int`, etc.). Note that for `bool` values, `false` wil be omitted if this option is used since this is the default empty value. To work around this, use `*bool` (see example) 
 
 For an example that includes all the above scenarios see the code below:
 
@@ -139,6 +141,23 @@ type ObjThree struct {
 	Name  string `custom:"name"`
 	Value int    `custom:"value"`
 }
+type ObjFour struct {
+    F1 string `custom:"f1,omitempty"`
+    F2 struct {
+        F21 string `custom:"f21,omitempty"`
+    } `custom:"f2"`
+    F3 *string     `custom:"f3, omitempty"` // omitempty with space
+    F4 int         `custom:"f4,omitempty"`
+    F5 bool        `custom:"f5,omitempty"`
+    F6 interface{} `custom:"f6,omitempty"`
+    F7 struct {
+        F71 string `custom:"f71"`
+    } `custom:"f7,omitempty"`
+    F8 *bool `custom:"f8,omitempty"` // use pointer to keep false on omitempty
+    F9 struct {
+        F91 string `custom:"f91"`
+    } `custom:"f9,omitempty"`
+}
 type Example struct {
 	Name     string     `custom:"name"`
 	Email    string     `custom:"email"`
@@ -148,10 +167,12 @@ type Example struct {
 	Id       int        `custom:"id"`
 	Call     int        `custom:"data.call"` // top-level dot notation
 	ArrayObj []ObjThree `custom:"list"`
+	Omit     ObjFour    `custom:omit`
 }
 ```
 The `ToMap` function can be used to convert this into a JSON/Map based on the values defined in the given custom tag like so.
 ```go
+f := false
 obj := Example{
     Name:  "2",
     Email: "3",
@@ -170,7 +191,12 @@ obj := Example{
         {"hi", 1},
         {"world", 2},
     },
+	Omit: ObjFour{
+      F5: f,
+      F8: &f,
+    }
 }
+obj.Omit.F9.F91 = "123"
 
 // get the map from custom tags
 tagName = "custom"
@@ -212,7 +238,13 @@ This will produce a result similar to:
             "name": "world",
             "value": 2
         }
-    ]
+    ],
+    "omit": {
+        "f8": false,
+        "f9": {
+            "f91": "123"
+        }
+    }
 }
 ```
 ---

map.go

@@ -9,6 +9,8 @@ import (
 
 var tagName = "" // initialise the struct tag value
 
+const omitEmptyTagOption = "omitempty" // omit values with this tag option if empty
+
 // getMapOfAllKeyValues builds a map of the fully specified key and the value from the struct tag
 // the struct tags with the full dot notation will be used as the key, and the value as the value
 // slices will be also be maps
@@ -65,10 +67,17 @@ func getMapOfAllKeyValues(s interface{}) *map[string]interface{} {
 				continue
 			}
 		} else {
+			// omitempty tag passed?
+			tag, shouldOmitEmpty := shouldOmitEmpty(tag) // overwrite tag
 			// recursive check nested fields in case this is a struct
 			if t.Field(i).Kind() == reflect.Struct {
 				// only check if the value can be obtained without panicking (eg: for unexported fields)
 				if t.Field(i).CanInterface() {
+					if shouldOmitEmpty {
+						if t.Field(i).IsZero() {
+							continue
+						}
+					}
 					qVars := getMapOfAllKeyValues(t.Field(i).Interface()) //recursive call
 					if qVars != nil {
 						for k, v := range *qVars {
@@ -79,6 +88,11 @@ func getMapOfAllKeyValues(s interface{}) *map[string]interface{} {
 			} else {
 				// only check if the value can be obtained without panicking (eg: for unexported fields)
 				if t.Field(i).CanInterface() {
+					if shouldOmitEmpty {
+						if t.Field(i).IsZero() {
+							continue
+						}
+					}
 					vars[tag] = t.Field(i).Interface()
 				}
 			}
@@ -119,6 +133,20 @@ func getMapOfAllKeyValues(s interface{}) *map[string]interface{} {
 	return &finalMap
 }
 
+// shouldOmitEmpty checks if the omitEmptyTagOption option is passed in the tag
+// eg: `foo:"bar,omitempty"`
+func shouldOmitEmpty(originalTag string) (string, bool) {
+	if ss := strings.Split(originalTag, ","); len(ss) > 1 {
+		// TODO: add more validation & error checking
+		if strings.TrimSpace(ss[1]) == omitEmptyTagOption {
+			return ss[0], true
+		}
+		return ss[0], false
+	} else {
+		return originalTag, false
+	}
+}
+
 // buildMap builds the parent map and calls buildNestedMap to create the child maps based on dot notation
 func buildMap(s []string, value interface{}, parent *map[string]interface{}) error {
 	var obj = make(map[string]interface{})
@@ -143,6 +171,10 @@ func ToMap(obj interface{}, tag string) (*map[string]interface{}, error) {
 	tagName = tag
 	s := getMapOfAllKeyValues(obj)
 
+	if s == nil {
+		return nil, fmt.Errorf("no valid map could be formed")
+	}
+
 	var parentMap = make(map[string]interface{})
 	for k, v := range *s {
 		keys := strings.Split(k, ".")

map_test.go

@@ -171,7 +171,7 @@ func TestNilAndUnexportedFields(t *testing.T) {
 		f1 string `custom:"f1"`
 		F2 struct {
 			F21 string `custom:"f21"`
-		} `custom:"age"`
+		} `custom:"f2"`
 		F3 *string     `custom:"f3"`
 		F4 int         `custom:"f4"`
 		F5 interface{} `custom:"f5"`
@@ -204,3 +204,54 @@ func TestNilAndUnexportedFields(t *testing.T) {
 	// compare
 	require.JSONEqf(t, expectedJSON, string(actualJSON), "JSON mismatch")
 }
+
+// TestOmitEmptyOptionFields calls ToMap function and checks for the expected behaviour
+// of passing the omitempty tag option
+func TestOmitEmptyOptionFields(t *testing.T) {
+	type MyStruct struct {
+		F1 string `custom:"f1,omitempty"`
+		F2 struct {
+			F21 string `custom:"f21,omitempty"`
+		} `custom:"f2"`
+		F3 *string     `custom:"f3, omitempty"` // omitempty with space
+		F4 int         `custom:"f4,omitempty"`
+		F5 bool        `custom:"f5,omitempty"`
+		F6 interface{} `custom:"f6,omitempty"`
+		F7 struct {
+			F71 string `custom:"f71"`
+		} `custom:"f7,omitempty"`
+		F8 *bool `custom:"f8,omitempty"`
+		F9 struct {
+			F91 string `custom:"f91"`
+		} `custom:"f9,omitempty"`
+	}
+
+	f := false
+	obj := MyStruct{
+		F5: f,
+		F8: &f,
+	}
+	obj.F9.F91 = "123"
+
+	// expected response
+	expectedJSON := `{
+			"f8": false,
+			"f9": {
+				"f91": "123"
+			}
+		}
+	`
+
+	// get the map from custom tags
+	actual, err := ToMap(obj, "custom")
+	if err != nil {
+		t.Fail()
+	}
+	actualJSON, err := json.Marshal(actual)
+	if err != nil {
+		t.Fail()
+	}
+
+	// compare
+	require.JSONEqf(t, expectedJSON, string(actualJSON), "JSON mismatch")
+}