CODEWITHSUNDEEP
c++mongodbc++11bson
trax
trax

Reputation: 749

Mongodb c++ driver 3.0, not const arrays

I am trying to create an array with the content of a vector 

using bsoncxx::builder::stream;
auto doc = document{};
doc << "foo"
  << open_array;

for (auto i : v){
  doc << open_document << "bar" << i << close_document ;
}
doc << close_array;

I get the following error report:

error: no match for ‘operator<<’ (operand types are ‘bsoncxx::v0::builder::stream::document’ and ‘const bsoncxx::v0::builder::stream::open_document_type’)
       doc << open_document << "bar" << i << close_document ;

Any idea on how to do it?

Upvotes: 1

Views: 439

Answers (2)

hanumantmk
hanumantmk

Reputation: 661

The C++11 bson driver is actually hiding a bit more complexity under the stream style api than it at first appears.

The problem you're encountering is that there is type information encoded into the expression on each successive '<<', so from your original example you'll need to:

auto sz = 100;

// Note that we capture the return value of open_array
auto arr = doc << "foo" << open_array;

for (int32_t i=0; i < sz; i++)
    arr << i;

arr << close_array;

This is because open_array creates a nested type that can accept values without keys, unlike doc, which needs key value pairs.

If you want something more inline, you can use the inline Callable facility as in:

auto sz = 100;
builder::stream::document doc;
doc << "foo" << open_array <<
    [&](array_context<> arr){
        for (int32_t i = 0; i < sz; i++)
            arr << i;
    } // Note that we don't invoke the lambda
<< close_array;

The callable facility works with things that take:

single_context - write one value in an array, or as the value part of a key value pair

key_context<> - write any number of key value pairs

array_context<> - write any number of values

See src/bsoncxx/test/bson_builder.cpp for more examples

Upvotes: 2

Nick
Nick

Reputation: 11

I have the same problem with the streaming builder. 

using bsoncxx::builder::stream;
auto doc = document{};
doc << "foo"
    << open_array
    << open_document
    << "bar1" << 1 
    << "bar2" << 5
    << close_document
    << close_array;

The above works, however if you want to do the following it doesn't work

doc << "foo"
    << open_array;
for (size_t i=0; i < sz; i++)
    doc << i;

doc << close_array;

I get the below error. The problem is that this behavior making using the stream builder is practically useless. Perhaps its a bug or the 10gen guys are not finished with the this part of the API. 

doc << closerror: no match for ‘operator<<’ (operand types are ‘bsoncxx::v0::builder::stream::document’ and ‘const bsoncxx::v0::builder::stream::open_document_type’) doc << open_document << "bar" << i << close_document ;e_array;

Upvotes: 1

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