# assert alice.to_plain_json == """
# {"name": "Alice", "year_of_birth": 1978, "next_of_kin": {"name": "Bob", "year_of_birth": 1986, "next_of_kin": null}}"""
# ~~~
+#
+# ## JSON to Nit objects
+#
+# The `JsonDeserializer` support reading JSON code with minimal meta-data
+# to easily create Nit object from client-side code or configuration files.
+# Each JSON object must define the `__class` attribute with the corresponding
+# Nit class and the expected attributes with its name in Nit followed by its value.
+#
+# ### Usage Example
+#
+# ~~~nitish
+# import json::serialization
+#
+# class MeetupConfig
+# serialize
+#
+# var description: String
+# var max_participants: nullable Int
+# var answers: Array[FlatString]
+# end
+#
+# var json_code = """
+# {"__class": "MeetupConfig", "description": "My Awesome Meetup", "max_participants": null, "answers": ["Pepperoni", "Chicken"]}"""
+# var deserializer = new JsonDeserializer(json_code)
+#
+# var meet = deserializer.deserialize
+# assert meet isa MeetupConfig
+# assert meet.description == "My Awesome Meetup"
+# assert meet.max_participants == null
+# assert meet.answers == ["Pepperoni", "Chicken"]
+# ~~~
module serialization
import ::serialization::caching
private import ::serialization::engine_tools
-private import static
+import static
# Serializer of Nit objects to Json string.
class JsonSerializer
end
end
- if not object.keys.has("__class") then
+ var class_name = object.get_or_null("__class")
+ if class_name == null then
+ # Fallback to custom heuristic
+ class_name = class_name_heuristic(object)
+ end
+
+ if class_name == null then
errors.add new Error("Serialization Error: JSON object declaration does not declare a `__class`.")
return object
end
- var class_name = object["__class"]
if not class_name isa String then
errors.add new Error("Serialization Error: JSON object declaration declares a non-string `__class`.")
return object
return object
end
+ # Simple JSON array without serialization metadata
if object isa Array[nullable Object] then
- # special case, isa Array[nullable Serializable]
- var array = new Array[nullable Serializable]
- for e in object do array.add e.as(nullable Serializable)
+ var array = new Array[nullable Object]
+ var types = new HashSet[String]
+ var has_nullable = false
+ for e in object do
+ var res = convert_object(e)
+ array.add res
+
+ if res != null then
+ types.add res.class_name
+ else has_nullable = true
+ end
+
+ if types.length == 1 then
+ var array_type = types.first
+
+ var typed_array
+ if array_type == "FlatString" then
+ if has_nullable then
+ typed_array = new Array[nullable FlatString]
+ else typed_array = new Array[FlatString]
+ else if array_type == "Int" then
+ if has_nullable then
+ typed_array = new Array[nullable Int]
+ else typed_array = new Array[Int]
+ else if array_type == "Float" then
+ if has_nullable then
+ typed_array = new Array[nullable Float]
+ else typed_array = new Array[Float]
+ else
+ # TODO support all array types when we separate the constructor
+ # `from_deserializer` from the filling of the items.
+
+ if not has_nullable then
+ typed_array = new Array[Object]
+ else
+ # Unsupported array type, return as `Array[nullable Object]`
+ return array
+ end
+ end
+
+ assert typed_array isa Array[nullable Object]
+
+ # Copy item to the new array
+ for e in array do typed_array.add e
+ return typed_array
+ end
+
+ # Uninferable type, return as `Array[nullable Object]`
return array
end
return object
end
- redef fun deserialize do return convert_object(root)
+ redef fun deserialize
+ do
+ errors.clear
+ return convert_object(root)
+ end
+
+ # User customizable heuristic to get the name of the Nit class to deserialize `json_object`
+ #
+ # This method is called only when deserializing an object without the metadata `__class`.
+ # Return the class name as a `String` when it can be inferred.
+ # Return `null` when the class name cannot be found.
+ #
+ # If a valid class name is returned, `json_object` will then be deserialized normally.
+ # So it must contain the attributes of the corresponding class, as usual.
+ #
+ # ~~~nitish
+ # class MyData
+ # serialize
+ #
+ # var data: String
+ # end
+ #
+ # class MyError
+ # serialize
+ #
+ # var error: String
+ # end
+ #
+ # class MyJsonDeserializer
+ # super JsonDeserializer
+ #
+ # redef fun class_name_heuristic(json_object)
+ # do
+ # if json_object.keys.has("error") then return "MyError"
+ # if json_object.keys.has("data") then return "MyData"
+ # return null
+ # end
+ # end
+ #
+ # var json = """{"data": "some other data"}"""
+ # var deserializer = new MyJsonDeserializer(json)
+ # var deserialized = deserializer.deserialize
+ # assert deserialized isa MyData
+ #
+ # json = """{"error": "some error message"}"""
+ # deserializer = new MyJsonDeserializer(json)
+ # deserialized = deserializer.deserialize
+ # assert deserialized isa MyError
+ # ~~~
+ protected fun class_name_heuristic(json_object: JsonObject): nullable String
+ do
+ return null
+ end
+end
+
+redef class Text
+
+ # Deserialize a `nullable Object` from this JSON formatted string
+ #
+ # Warning: Deserialization errors are reported with `print_error` and
+ # may be returned as a partial object or as `null`.
+ #
+ # This method is not appropriate when errors need to be handled programmatically,
+ # manually use a `JsonDeserializer` in such cases.
+ fun from_json_string: nullable Object
+ do
+ var deserializer = new JsonDeserializer(self)
+ var res = deserializer.deserialize
+ if deserializer.errors.not_empty then
+ print_error "Deserialization Errors: {deserializer.errors.join(", ")}"
+ end
+ return res
+ end
+
+ redef fun serialize_to_json(v) do v.stream.write(to_json)
end
redef class Serializable
v.stream.write "\}"
end
+ # Serialize this object to a JSON string with metadata for deserialization
+ fun to_json_string: String
+ do
+ var stream = new StringWriter
+ var serializer = new JsonSerializer(stream)
+ serializer.serialize self
+ stream.close
+ return stream.to_s
+ end
+
# Serialize this object to plain JSON
#
# This is a shortcut using `JsonSerializer::plain_json`,
end
end
-redef class String
- redef fun serialize_to_json(v) do v.stream.write(to_json)
-end
-
redef class NativeString
redef fun serialize_to_json(v) do to_s.serialize_to_json(v)
end
v.stream.write id.to_s
v.stream.write """, "__class": """"
v.stream.write class_name
- v.stream.write """", "__length": """
- v.stream.write length.to_s
- v.stream.write """, "__items": """
+ v.stream.write """", "__items": """
end
serialize_to_pure_json v
end
end
- redef init from_deserializer(v: Deserializer)
+ redef init from_deserializer(v)
do
super
if v isa JsonDeserializer then
v.notify_of_creation self
init
- var length = v.deserialize_attribute("__length").as(Int)
var arr = v.path.last["__items"].as(SequenceRead[nullable Object])
- for i in length.times do
- var obj = v.convert_object(arr[i])
+ for o in arr do
+ var obj = v.convert_object(o)
self.add obj
end
end
end
end
-redef class Array[E]
- redef fun serialize_to_json(v)
- do
- if v.plain_json or class_name == "Array[nullable Serializable]" then
- # Using class_name to get the exact type,
- # we do not want Array[Int] or anything else here.
-
- serialize_to_pure_json v
- else super
- end
-end
-
redef class Map[K, V]
redef fun serialize_to_json(v)
do
end
end
- # Instantiate a new `Array` from its serialized representation.
- redef init from_deserializer(v: Deserializer)
+ redef init from_deserializer(v)
do
super
nitlanguage / nit.git / blobdiff