Merge pull request #3 from nyaruka/json

add json nullable type

null.go

@@ -238,3 +238,64 @@ func (m *Map) UnmarshalJSON(data []byte) error {
 	}
 	return json.Unmarshal(data, &m.m)
 }
+
+// JSON is a json.RawMessage that will marshall as null when empty or nil.
+// null and {} values when unmashalled or scanned from a DB will result in a nil value
+type JSON json.RawMessage
+
+// Scan implements the Scanner interface for decoding from a database
+func (j *JSON) Scan(src interface{}) error {
+	if src == nil {
+		*j = nil
+		return nil
+	}
+
+	var source []byte
+	switch src.(type) {
+	case string:
+		source = []byte(src.(string))
+	case []byte:
+		source = src.([]byte)
+	default:
+		return fmt.Errorf("incompatible type for JSON type")
+	}
+
+	if !json.Valid(source) {
+		return fmt.Errorf("invalid json: %s", source)
+	}
+	*j = source
+	return nil
+}
+
+// Value implements the driver Valuer interface
+func (j JSON) Value() (driver.Value, error) {
+	if len(j) == 0 {
+		return nil, nil
+	}
+	return []byte(j), nil
+}
+
+// MarshalJSON encodes our JSON to JSON or null
+func (j JSON) MarshalJSON() ([]byte, error) {
+	if len(j) == 0 {
+		return json.Marshal(nil)
+	}
+	return []byte(j), nil
+}
+
+// UnmarshalJSON sets our JSON from the passed in JSON
+func (j *JSON) UnmarshalJSON(data []byte) error {
+	if string(data) == "null" {
+		*j = nil
+		return nil
+	}
+
+	var jj json.RawMessage
+	err := json.Unmarshal(data, &jj)
+	if err != nil {
+		return err
+	}
+
+	*j = JSON(jj)
+	return nil
+}

null_test.go

@@ -4,6 +4,7 @@ import (
 	"database/sql"
 	"database/sql/driver"
 	"encoding/json"
+	"strings"
 	"testing"
 
 	_ "github.com/lib/pq"
@@ -368,3 +369,78 @@ func TestMap(t *testing.T) {
 		assert.Equal(t, m2.GetString(tc.Key, ""), tc.KeyValue)
 	}
 }
+
+func TestJSON(t *testing.T) {
+	db, err := sql.Open("postgres", "postgres://localhost/null_test?sslmode=disable")
+	assert.NoError(t, err)
+
+	_, err = db.Exec(`DROP TABLE IF EXISTS json_test; CREATE TABLE json_test(value jsonb null);`)
+	assert.NoError(t, err)
+
+	sp := func(s string) *string {
+		return &s
+	}
+
+	tcs := []struct {
+		Value JSON
+		JSON  json.RawMessage
+		DB    *string
+	}{
+		{JSON(`{"foo":"bar"}`), json.RawMessage(`{"foo":"bar"}`), sp(`{"foo":"bar"}`)},
+		{JSON(nil), json.RawMessage(`null`), nil},
+		{JSON([]byte{}), json.RawMessage(`null`), nil},
+	}
+
+	for i, tc := range tcs {
+		// first test marshalling and unmarshalling to JSON
+		b, err := json.Marshal(tc.Value)
+		assert.NoError(t, err)
+		assert.Equal(t, string(tc.JSON), string(b), "%d: marshalled json not equal", i)
+
+		j := JSON("blah")
+		err = json.Unmarshal(tc.JSON, &j)
+		assert.NoError(t, err)
+		assert.Equal(t, string(tc.Value), string(j), "%d: unmarshalled json not equal", i)
+
+		// ok, now test writing and reading from DB
+		_, err = db.Exec(`DELETE FROM json_test;`)
+		assert.NoError(t, err)
+
+		_, err = db.Exec(`INSERT INTO json_test(value) VALUES($1)`, tc.DB)
+		assert.NoError(t, err)
+
+		rows, err := db.Query(`SELECT value FROM json_test;`)
+		assert.NoError(t, err)
+
+		assert.True(t, rows.Next())
+		j = JSON("blah")
+		err = rows.Scan(&j)
+		assert.NoError(t, err)
+
+		if tc.Value == nil {
+			assert.Nil(t, j, "%d: read db value should be null", i)
+		} else {
+			assert.Equal(t, string(tc.Value), strings.Replace(string(j), " ", "", -1), "%d: read db value should be equal", i)
+		}
+
+		_, err = db.Exec(`DELETE FROM json_test;`)
+		assert.NoError(t, err)
+
+		_, err = db.Exec(`INSERT INTO json_test(value) VALUES($1)`, tc.Value)
+		assert.NoError(t, err)
+
+		rows, err = db.Query(`SELECT value FROM json_test;`)
+		assert.NoError(t, err)
+
+		assert.True(t, rows.Next())
+		var s *string
+		err = rows.Scan(&s)
+		assert.NoError(t, err)
+
+		if tc.DB == nil {
+			assert.Nil(t, s, "%d: written db value should be null", i)
+		} else {
+			assert.Equal(t, *tc.DB, strings.Replace(*s, " ", "", -1), "%d: written db value should be equal", i)
+		}
+	}
+}