sub-object in sub-array in mongodb-C

问题

Here's the structure part of my collection :

{
   ...
   list: [
      { id:'00A', name:'None 1' },
      { id:'00B', name:'None 2' },
   ],
   ...
}

Which method could you advise me to retrieve the list of values in the "id" and/or "name" field with C lib please ?

回答1:

It seems you are asking for the equivalent of "db.collection.distinct" with the C driver. Is that correct? If so, you can issue distinct as a db command using the mongo_run_command function:

http://api.mongodb.org/c/current/api/mongo_8h.html#a155e3de9c71f02600482f10a5805d70d

Here is a piece of code you may find useful demonstrating the implementation:

mongo conn[1];
int status = mongo_client(conn, "127.0.0.1", 27017);

if (status != MONGO_OK)
    return 1;

bson b[1]; // query bson
bson_init(b);
bson_append_string(b, "distinct", "foo");
bson_append_string(b, "key", "list.id"); // or list.name
bson_finish(b);

bson bres[1]; // result bson

status = mongo_run_command(conn, "test", b, bres);

if (status == MONGO_OK){
    bson_iterator i[1], sub[1];
    bson_type type;
    const char* val;

    bson_find(i, bres, "values");
    bson_iterator_subiterator(i, sub);

    while ((type = bson_iterator_next(sub))) {
        if (type == BSON_STRING) {
            val = bson_iterator_string(sub);
            printf("Value: %s\n", val);
        }
    }
} else {
    printf("error: %i\n", status);
}

The database is "foo" and the collection, containing documents similar to yours, is "test" in the above example. The query portion of the above is equivalent to:

db.runCommand({distinct:'foo', key:'list.id'})

Hope that helps.

Jake

来源：https://stackoverflow.com/questions/18719542/sub-object-in-sub-array-in-mongodb-c

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mongodb

bson

mongodb-c