mongodb-erlang Erlang driver examples

Question

Where i can find examples of mongodb-erlang usage ? The only source of information i found is this file: https://github.com/TonyGen/mongodb-erlang/blob/master/src/mongodb_tests.erl But it not covers many of basic queries like following (picked from MongoDB site):

db.collection.find().sort({name : 1, age: -1}).limit(10);
db.users.find().skip(20).limit(10);
db.things.ensureIndex({j:1});
db.things.find({colors : {$ne : "red"}});
db.collection.find({ "field" : { $gte: value } } );
db.things.find( { "x.a" : 1, "x.b" : { $gt : 1 } } )

So how to write these queries in terms of erlang driver ?

Answer 1

I have this similar issues too, here is my resolution with the offical mongodb-erlang driver:

1.The test mongodb records:

>db.erltest.find()
{ "_id" : ObjectId("4fe80d692f6cc055a32da380"), "x" : 1, "y" : 2 }
{ "_id" : ObjectId("4fe80d702f6cc055a32da381"), "x" : 2, "y" : 3 }
{ "_id" : ObjectId("4fe80d762f6cc055a32da382"), "x" : 10, "y" : 3 }
{ "_id" : ObjectId("4fe80d7e2f6cc055a32da383"), "x" : 10, "y" : 4 }

2.How to implement "db.erltest.find({x:{$gt:2}})" via mongodb-erlang?

-module(mongo_test2).
-export([tmp_test/0]).
-include ("/opt/Erlang/lib/erlang/lib/mongodb-master/include/mongo_protocol.hrl").

tmp_test() ->
    application:start(mongodb),
    Host = {localhost, 27017},
    {ok, Conn} = mongo:connect(Host),
    io:format("Conn is : ~p~n", [Conn]),
    DbConn = {test, Conn},
    Cursor = mongo_query:find(DbConn, #'query'{collection=erltest, selector={x, {'$gt', 2}}}),
    process(Cursor),
    mongo:disconnect(Conn).

process({}) ->
    ok;
process(Cursor) ->
    io:format("----Cursor:~p~n", [Cursor]),
    Record = mongo:next(Cursor),
    io:format("Record:~p~n", [Record]),
    case Record of 
        {} ->
            no_more;
        _ ->        
            process(Cursor)
    end.

Summaries:

1. Please ensure include the correct path with the *mongo_protocol.hrl* file.
2. Cursor = mongo_query:find(DbConn, #'query'{collection=erltest, selector={x, {'$gt', 2}}}) is the detailed implement.
3. Maybe mongodb_test.erl can supply more details for you.
4. I'm an erlang newbie, for finding the above usage take me some time, hope this is helpful for you :)

Answer 2

For the officially supported driver the API is documented here:

http://api.mongodb.org/erlang/mongodb/

For the find operations check out the function index, specifically:

http://api.mongodb.org/erlang/mongodb/mongo.html#find-2

If that is not to your taste, you may want to also check out the community drivers:

emongo/erlmongo - their respective READMEs and docs have some examples too:

https://bitbucket.org/rumataestor/emongo

https://github.com/wpntv/erlmongo