NAME

       bson_creating - Creating a BSON Document

THE BSON_T STRUCTURE

       BSON  documents  are  created  using the bson_t structure. This structure encapsulates the
       necessary logic for encoding using the BSON Specification. At the core, bson_t is a buffer
       manager and set of encoding routines.

       TIP:
          BSON  documents  can  live  on  the stack or the heap based on the performance needs or
          preference of the consumer.

       Let's start by creating a new BSON document on the stack.  Whenever  using  libbson,  make
       sure you #include <bson.h>.

          bson_t b;

          bson_init (&b);

       This creates an empty document. In JSON, this would be the same as {}.

       We  can  now proceed to adding items to the BSON document. A variety of functions prefixed
       with bson_append_ can be used based on the type of field you want to append. Let's  append
       a UTF-8 encoded string.

          bson_append_utf8 (&b, "key", -1, "value", -1);

       Notice  the  two -1 parameters. The first indicates that the length of key in bytes should
       be determined with strlen(). Alternatively, we could have passed the number  3.  The  same
       goes for the second -1, but for value.

       Libbson  provides  macros  to  make  this  less  tedious  when  using string literals. The
       following two appends are identical.

          bson_append_utf8 (&b, "key", -1, "value", -1);
          BSON_APPEND_UTF8 (&b, "key", "value");

       Now let's take a look at an example that adds a  few  different  field  types  to  a  BSON
       document.

          bson_t b = BSON_INITIALIZER;

          BSON_APPEND_INT32 (&b, "a", 1);
          BSON_APPEND_UTF8 (&b, "hello", "world");
          BSON_APPEND_BOOL (&b, "bool", true);

       Notice  that  we  omitted  the  call to bson_init(). By specifying BSON_INITIALIZER we can
       remove the need to initialize the structure to a base state.

SUB-DOCUMENTS AND SUB-ARRAYS

       To simplify the creation of sub-documents  and  arrays,  bson_append_document_begin()  and
       bson_append_array_begin()  exist.  These  can  be  used  to build a sub-document using the
       parent documents memory region as the destination buffer.

          bson_t parent;
          bson_t child;
          char *str;

          bson_init (&parent);
          bson_append_document_begin (&parent, "foo", 3, &child);
          bson_append_int32 (&child, "baz", 3, 1);
          bson_append_document_end (&parent, &child);

          str = bson_as_canonical_extended_json (&parent, NULL);
          printf ("%s\n", str);
          bson_free (str);

          bson_destroy (&parent);

          { "foo" : { "baz" : 1 } }

SIMPLIFIED BSON C OBJECT NOTATION

       Creating BSON documents by hand can be tedious and time consuming. BCON, or BSON C  Object
       Notation,  was  added  to  allow for the creation of BSON documents in a format that looks
       closer to the destination format.

       The following example shows the use of BCON. Notice that values for fields are wrapped  in
       the  BCON_*  macros.  These  are  required  for  the  variadic  processor to determine the
       parameter type.

          bson_t *doc;

          doc = BCON_NEW ("foo",
                          "{",
                          "int",
                          BCON_INT32 (1),
                          "array",
                          "[",
                          BCON_INT32 (100),
                          "{",
                          "sub",
                          BCON_UTF8 ("value"),
                          "}",
                          "]",
                          "}");

       Creates the following document

          { "foo" : { "int" : 1, "array" : [ 100, { "sub" : "value" } ] } }

AUTHOR

       MongoDB, Inc

COPYRIGHT

       2018, MongoDB, Inc