Convert from Rapidjson Value to Rapidjson Document - c++

Question

As per the tutorial:
Each JSON value is stored in a type called Value. A Document, representing the DOM, contains the root Value of the DOM tree.
If so, it should be possible to make a sub-document from a document.
If my JSON is:
{
"mydict": {
"inner dict": {
"val": 1,
"val2": 2
}
}
}
I'd like to be able to create a Document from the inner dictionary.
(And then follow the instructions in the FAQ for How to insert a document node into another document?)

Answer 1

Given the original document contains:
{
"mydict": {
"inner dict": {
"val": 1,
"val2": 2
}
}
}
You can copy the sub-document:
const char json[] = "{\"mydict\": {\"inner dict\": {\"val\": 1, \"val2\": 2}}}";
Document doc, sub; // Null
doc.Parse(json);
sub.CopyFrom(doc["mydict"], doc.GetAllocator());
You can also swap the sub-document with another:
const char json[] = "{\"mydict\": {\"inner dict\": {\"val\": 1, \"val2\": 2}}}";
Document doc, sub; // Null
doc.Parse(json);
sub.Swap(doc["mydict"]);
With some validation:
const char json[] = "{\"mydict\": {\"inner dict\": {\"val\": 1, \"val2\": 2}}}";
Document doc, sub; // Null
doc.Parse(json);
if (doc.IsObject()) {
auto it = doc.FindMember("mydict");
if (it != doc.MemberEnd() && it->value.IsObject()) {
sub.Swap(it->value);
}
}
Each will result in sub containing:
{
"inner dict": {
"val": 1,
"val2": 2
}
}
With the CopyFrom() approach, doc will contain:
{
"mydict": {
"inner dict": {
"val": 1,
"val2": 2
}
}
}
With Swap():
{
"mydict": null
}