Question

I want to use mongodb as a map in Erlang. I cannot find an example of this. This is what I have so far:

application:start(mongodb).
Host = {localhost, 27017}.
{ok, Conn} = mongo:connect(Host).

mongo:do(safe, master, Conn, test, fun() ->
    mongo:delete(foo, {}),                 
    mongo:insert(foo, {x,1}),
    mongo:insert(foo, {a,12}),
    Pid = mongo:find(foo, {a}),    
    Result = mongo_cursor:rest(Pid),                
    mongo_cursor:close(Pid),
    Result end).

Result:

{ok,[{'_id',{<<80,138,211,178,41,152,132,104,251,0,0,35>>},
            x,1},
     {'_id',{<<80,138,211,178,41,152,132,104,251,0,0,36>>},
            a,12}]}

Why does it create two maps?

Answer 1

You are doing two inserts into MongoDB without specifying any _id value, so end up with two documents and an autogenerated unique ObjectId. If you are trying to use a collection similar to a map or dict, you should be providing an _id value as the key and use repsert (aka upsert) to update the document if it exists already (or insert if it doesn’t).