How to get collection names in the database?

[BlaCatRu]

Help pls

• "mc_worker_api:command(Connection,{<<"listDatabases">>,1})" works fine and returns a basic info about all existing databases
• but listCollections command has another output and returns the cursor and the first batch

How cat I get results similar to the db.getCollectionNames method?

[comtihon]

Hi, You can get all the results from cursor by calling mc_cursor:rest/1

[BlaCatRu]

Hi, There is another kind of the cursor i think. And mc_cursor:rest/1 fails :-(

{ok,<0.120.0>}
2> {true, Res} = mc_worker_api:command(Connection,{<<"listCollections">>,1}).
{true,#{<<"cursor">> => #{<<"firstBatch">> => [#{<<"idIndex">> => #{<<"key">> => #{<<"_id">> => 1},
               <<"name">> => <<"_id_">>,
               <<"ns">> => <<"xxxdb.xxx.collection">>,
               <<"v">> => 1},
             <<"info">> => #{<<"readOnly">> => false},
             <<"name">> => <<"xxx.collection">>,
             <<"options">> => #{},
             <<"type">> => <<"collection">>},
           #{<<"idIndex">> => #{<<"key">> => #{<<"_id">> => 1},
               <<"name">> => <<"_id_">>,
               <<"ns">> => <<"xxxdb.xxx.collection">>,
               <<"v">> => 1},
             <<"info">> => #{<<"readOnly">> => false},
             <<"name">> => <<"xxx.collection">>,
             <<"options">> => #{},
             <<"type">> => <<"collection">>}],
          <<"id">> => 0,
          <<"ns">> => <<"xxxdb.$cmd.listCollections">>}}}
3> mc_cursor:rest(Res).
** exception exit: {{function_clause,[{gen,do_for_proc,
...```

Description of this cursor from docs:
**listCollections.cursor**
A document that contains information with which to create a cursor to documents that contain    collection names and options. The cursor information includes the cursor id, the full namespace for the command, as well as the first batch of results.

[comtihon]

Thanks, I'll check it.

[dmsnell]

@BlaCatRu did you ever figure it out?

[dmsnell]

From my own exploration I believe that the response is returning the full list of collections inside of the <<"firstBatch">> field. I tried this on a database with a few hundred collections and it never indicated that there were more batches. Also the cursor id returned from the query seems to be invalid. I believe this is a special case for the commands.