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katlv_zheng
Mar 2024

I am developing a project using GridFS to save large files as binary blob into MongoDB; I am using C++ API;

So far I am able to save large files into bucket, which in mongosh gives me two collections fs.chunks and fs.files;

However, I have problems to delete files from the bucket. I tried to use the C++ API and below are the code snip I am using:

# code that successfully assign "doc" as bsoncxx::v_noabi::document::view&
bucket.delete_file(doc["_id"].get_oid().value.to_string());

or
bucket.delete_file(doc["_id"].get_oid().value);

or even
bucket.delete_file(doc["_id"].get_oid());

None of the above code allow me to compile my code, error message always says

error: no matching function for call to ‘mongocxx::v_noabi::gridfs::bucket::delete_file(bsoncxx::v_noabi::document::view&)’ 
or similar input type not match delete_file() input variable.

I looked the official document says that the delete_file() accept and input variable “id” can be the type of
[bsoncxx::v_noabi::types::bson_value::view
which means anything in BSON;

But even I tried to convert the oid to a bson_value object does not fix the problem. I suspect there could be some bugs in the function? And I would like to seek help or advice from community. Thanks again.
Rishabh_BishtMongoDB Employee
Mar 2024

Hi @katlv_zheng

Welcome to MongoDB forums!

You need to convert the _id field of your document to a bsoncxx::types::bson_value::view using the bsoncxx::types::bson_value::view_or_value constructor. I have shared sample code below.

// ---------------UPLOAD---------------//
    
     // "sample_gridfs_file" is the name of the GridFS file stored on the server.
    auto uploader = bucket.open_upload_stream("sample_gridfs_file");

    // ASCII for "HelloWorld"
    std::uint8_t bytes[10] = {72, 101, 108, 108, 111, 87, 111, 114, 108, 100};

    // Write 50 bytes to the file.
    for (auto i = 0; i < 5; ++i) {
        uploader.write(bytes, 10);
    }

    auto result = uploader.close();

    // // ---------------DELETE---------------//

    // Delete the uploaded file by using the id. 
    // "id" can be reused directly, but construct a document for the sake of example.
    bsoncxx::types::bson_value::view id = result.id();
    bsoncxx::document::value doc_value = bsoncxx::builder::basic::make_document(bsoncxx::builder::basic::kvp("_id", id));
    bsoncxx::document::view doc_view = doc_value.view();
    
    bsoncxx::types::bson_value::view_or_value id_value {doc_view["_id"].get_value()};
    
    // Pass the id to the delete_file
    bucket.delete_file(id_value);
katlv_zheng
Mar 2024

Hi Rishabh, thanks the sample code and it solves my problem. Didn’t expect the syntax need to be like this though. Thanks again!

Closed on Mar 16, 2024

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