Add support for database json types.

types/types.go

@@ -0,0 +1,81 @@
+package types
+
+import (
+	"database/sql/driver"
+	"encoding/json"
+	"errors"
+)
+
+// JSONText is a json.RawMessage, which is a []byte underneath.
+// Value() validates the json format in the source, and returns an error if
+// the json is not valid.  Scan does no validation.  JSONText additionally
+// implements `Unmarshal`, which unmarshals the json within to an interface{}
+type JSONText json.RawMessage
+
+var emptyJSON = JSONText("{}")
+
+// MarshalJSON returns the *j as the JSON encoding of j.
+func (j JSONText) MarshalJSON() ([]byte, error) {
+	if len(j) == 0 {
+		return emptyJSON, nil
+	}
+	return j, nil
+}
+
+// UnmarshalJSON sets *j to a copy of data
+func (j *JSONText) UnmarshalJSON(data []byte) error {
+	if j == nil {
+		return errors.New("JSONText: UnmarshalJSON on nil pointer")
+	}
+	*j = append((*j)[0:0], data...)
+	return nil
+}
+
+// Value returns j as a value.  This does a validating unmarshal into another
+// RawMessage.  If j is invalid json, it returns an error.
+func (j JSONText) Value() (driver.Value, error) {
+	var m json.RawMessage
+	var err = j.Unmarshal(&m)
+	if err != nil {
+		return []byte{}, err
+	}
+	return []byte(j), nil
+}
+
+// Scan stores the src in *j.  No validation is done.
+func (j *JSONText) Scan(src interface{}) error {
+	if j == nil {
+		return errors.New("JSONText: Scan on nil pointer")
+	}
+
+	var source []byte
+	switch t := src.(type) {
+	case string:
+		source = []byte(t)
+	case []byte:
+		if len(t) == 0 {
+			source = emptyJSON
+		} else {
+			source = t
+		}
+	case nil:
+		*j = emptyJSON
+	default:
+		return errors.New("Incompatible type for JSONText")
+	}
+	*j = JSONText(append((*j)[0:0], source...))
+	return nil
+}
+
+// Unmarshal unmarshal's the json in j to v, as in json.Unmarshal.
+func (j *JSONText) Unmarshal(v interface{}) error {
+	if len(*j) == 0 {
+		*j = emptyJSON
+	}
+	return json.Unmarshal([]byte(*j), v)
+}
+
+// String supports pretty printing for JSONText types.
+func (j JSONText) String() string {
+	return string(j)
+}