mongo-cxx-driver-新的C ++ 11驱动程序-如何从二进制数据创建文档

Question

for a project I need a c++ implementation for bson. According to the BSON Specs there are serveral bson c++ implementations. I already tried each of them. Bson-cpp isnt supported anymore. Bson-cxx wont even compile on my debian stretch.

So I tried the official mongodb-cxx-driver. But i want to use the current master-branch of the driver which contains the new c++11 driver because it uses cmake as build system. I already managed to create a bson document and convert it to a binary array. My problem at the moment is that I don't get how to create a bson document from an array of binary data even after digging through their code for two hours.

Is this functionality even implemented at the moment ?

Answer 1

The C++11 driver from MongoDB offers a few interfaces for BSON writing and one interface for reading.

If what you want to do is read some already serialized bson:

bsoncxx::document::view view(data, length); // make a view
view["key"]; // fetch a key
view.find("key"); // map style iterator
for (auto x : view) {} // C++11 for loop

// or to load an array
bsoncxx::array::view view(data, length);
view[N];
// etc...

If you'd like to write some bson:

For a streaming api:

using namespace bsoncxx::builder::stream;
// Use builder::stream::array for array building
document b;

// Makes { "key" : "value", "subdoc" : { "sub key a" : 1 } }
b << "key" << "value" << "subdoc" <<
  << open_document << "sub key a" << 1 << close_document;

// to concatenate
b << concatenate(view);

// to use a non-deducible type like a sub doc
b << "key" << bsoncxx::types::b_document{view}

b.view() // gets a view

// take ownership of the bson bytes in a move only value type
bsoncxx::document::value v = b.extract()

For a simple key value api:

using namespace bsoncxx::builder::basic;

// Use builder::basic::array for array building
document b;

b.append(
    kvp("key", "value"),
    // Use sub_array for sub arrays
    kvp("subdoc", [](sub_document sd) {
        sd.append(kvp("sub key a", 1));
    })
);

That core api you found is certainly functional, but it's meant to provide a low level machine for BSON appending over a reallocing buffer, rather than an easy to use client interface. Prefer the builder::basic or builder::stream apis if you'd like some template magic to make construction more declarative.

Answer 2

After some more digging in their code I found the answer:

You can use:

bsoncxx::document::view(uint8_t* data, size_t length)

in order to create new view

Then you can use

bsoncxx::builder::core(bool isArray)

to create a new core .On this core you can call

core.concatenate(view)

to insert the view into the new core. Afterwards you can create new sub_document with:

bsoncxx::builder::basic:sub_document(core* c)

sub_document should provide all methods needed to extract the fields from the bson message.