This is the MongoDB driver for Erlang. MongoDB is a document-oriented database management system. A driver is a client library that provides an API for connecting to MongoDB servers, performing queries and updates on those servers, and performing administrative tasks like creating indexes and viewing statistics. This version of the driver supports connecting to a single server or replica set, and pooling of both types of connections. Both connection types and pools are thread-safe, i.e. multiple processes can use the same connection/pool simultaneously without interfering with each other. This driver is implemented as an Erlang application named mongodb. It depends on another Erlang library application named bson, which defines the document type and its standard binary representation. You need both of these. Below we describe the mongodb application; you should also see the bson application to understand the document type.
Download and compile the application
$ git clone git://github.com/mongodb/mongodb-erlang.git mongodb
$ cd mongodb
$ make
The bson application needs to be started before starting mongodb application
> application:start (bson).
The mongodb application needs be started before using (to initialize an internal ets table of counters)
> application:start (mongodb).
Although the mongodb application includes several modules, you should only need to use mongo, which is the top-level interface for the driver. Likewise, you should only need to use the bson module in the bson application.
To connect to a database test on mongodb server listening on localhost:27017 (or any address & port of your choosing)
use mongo:connect/3/4/6.
> Host = "127.0.0.1".
> Port = 27017.
> Database = <<"test">>.
> {ok, Connection} = mongo:connect (Host, Port, Database).
mongo:connect returns {error, Reason} if it failed to connect.
mongo:connect/4 also takes extra options as a param. It is timeout - time to wait for connection to database.
mongo:connect/6 also adds read and write modes config. They are master and slave_ok for read and unsafe, safe
and {safe, bson:document()} for write.
safe, along with {safe, GetLastErrorParams} and unsafe, are write-modes. Safe mode makes a getLastError request
after every write in the sequence. If the reply says it failed then the rest of the sequence is aborted and mongo:do
returns {failure, {write_failure, Reason}}, or {failure, not_master} when connected to a slave. An example write
failure is attempting to insert a duplicate key that is indexed to be unique. Alternatively, unsafe mode issues every
write without a confirmation, so if a write fails you won't know about it and remaining operations will be executed.
This is unsafe but faster because you there is no round-trip delay.
master, along with slave_ok, are read-modes. master means every query in the sequence must read fresh data (from
a master/primary server). If the connected server is not a master then the first read will fail, the remaining operations
will be aborted, and mongo:do will return {failure, not_master}. slave_ok means every query is allowed to read
stale data from a slave/secondary (fresh data from a master is fine too).
After you connected to your database - you can carry out write operations, such as insert, update and delete:
> Collection = <<"test">>.
> mongo:insert(Connection, Collection, [
{name, <<"Yankees">>, home, {city, <<"New York">>, state, <<"NY">>}, league, <<"American">>},
{name, <<"Mets">>, home, {city, <<"New York">>, state, <<"NY">>}, league, <<"National">>},
{name, <<"Phillies">>, home, {city, <<"Philadelphia">>, state, <<"PA">>}, league, <<"National">>},
{name, <<"Red Sox">>, home, {city, <<"Boston">>, state, <<"MA">>}, league, <<"American">>}
])
An insert example (from mongo_SUITE test module). Connection is your Connection, got from mongo:connect, Collection
is your collection name, Doc is something, you want to save.
Doc will be returned, if insert succeeded. If Doc doesn't contains _id field - an updated Doc will be returned - with
automatically generated '_id' fields. If error occurred - Connection will fall.
> mongo:delete(Connection, Collection, Selector).
Delete example. Connection is your Connection, Collection - is a collection you want to clean. Selector is the
rules for cleaning. If you want to clean everything - pass empty {}.
To call read operations use find, find_one:
> Cursor = mongo:find(Connection, Collection, Selector)
All params similar to delete.
The difference between find and find_one is in return. Find_one just returns your result, while find returns you a
Cursor - special process' pid. You can query data through the process with the help of `mc_cursor' module.
> Result = mc_cursor:rest(Cursor),
> mc_cursor:close(Cursor),
Important! Do not forget to close cursors after using them!
To search for params - specify Selector:
mongo:find_one(Connection, Collection, {key, <<"123">>}).
will return one document from collection Collection with key == <<"123">>.
mongo:find_one(Connection, Collection, {key, <<"123">>, value, <<"built_in">>}).
will return one document from collection Collection with key == <<"123">> and value == <<"built_in">>.
Tuples {key, <<"123">>} in first example and {key, <<"123">>, value, <<"built_in">>} are selectors.
For filtering result - use Projector:
mongo:find_one(Connection, Collection, {}, {value, true}).
will return one document from collection Collection with fetching only _id and value.
mongo:find_one(Connection, Collection, {}, {key, false, value, false}).
will return your data without key and value params. If there is no other data - only _id will be returned.
Important! For empty projector use [] instead {}. For empty selector use {}.
To add or update field in document - use mongo:update function with $set param.
This updates selected fields:
Command = {'$set', {
quantity, 500,
details, {model, "14Q3", make, "xyz"},
tags, ["coats", "outerwear", "clothing"]
}},
mongo:update(Connection, Collection, {'_id', 100}, Command),
This will add new field expired, if there is no such field, and set it to true.
Command = {'$set', {expired, true}},
mongo:update(Connection, Collection, {'_id', 100}, Command),
This will update fields in nested documents. Atoms using will be changed next version.
Command = {'$set', {'details.make', "zzz"}},
mongo:update(Connection, Collection, {'_id', 100}, Command),
This will update elements in array. Atoms using will be changed next version.
Command = {'$set', {
'tags.1', "rain gear",
'ratings.0.rating', 2
}},
mongo:update(Connection, Collection, {'_id', 100}, Command),
For result of executing this functions - see mongo_SUITE update test.
To create indexes - use mongo:ensure_index/3 command:
mongo:ensure_index(Connection, Collection, {key, {index, 1}}). %simple
mongo:ensure_index(Connection, Collection, {key, {index, 1}, name, <<"MyI">>}). %advanced
mongo:ensure_index(Connection, Collection, {key, {index, 1}, name, <<"MyI">>, unique, true, dropDups, true}). %full
ensure_index takes mc_worker' pid or atom name as first parameter, collection, where to create index, as second
parameter and bson document with index
specification - as third parameter. In index specification one can set all or only some parameters.
If index specification is not full - it is automatically filled with values: name, Name, unique, false, dropDups, false, where Name is index's key.
This driver does not provide helper functions for commands. Use mongo:command directly and refer to the
MongoDB documentation for how to issue raw commands.
To authenticate use function mongo:auth.
> mongo:auth(C, <<"admin">>, <<"123456">>).
The return values will be:
{false,{errmsg,<<"auth failed">>,code,18}}in case of failure{true,{dbname,<<"test">>,user,<<"admin">>}}in case of success. Plain Erlang string is interpreted as a BSON array of integers, so make sure to always encode your strings, as in<<"hello">>orbson:utf8("hello").
By default timeout for all connections to connection gen_server is infinity. If you found problems with it - you can
modify timeout.
To modify it just add mc_worker_call_timeout with new value to your applications's env config.
Timeout for operations with cursors may be explicity passed to mc_cursor:next/2, mc_cursor:take/3, mc_cursor:rest/2, and mc_cursor:foldl/5 functions, by default used value of cursor_timeout from application config, or infinity if cursor_timeout not specified.
For pooling use Poolboy with mc_worker as pool workers.
API Docs - Documentation generated from source code comments