map reduce with stored javascript functions

[Laura Dietz]

Dear List,

I have a combination of map-reduce commands that have to be performed in
that order.
Each map/reduce/finalize method is stored in db.system.js

I have another javascript function "doIt" ties all commands together
sets scope arguments etc.

I could save doIt in the db.system.js as well and call
db.eval("doIt()"), but for blocking reasons I don't want to do this.

However, if I just call doIt on the client, it can't resolve the
functions stored in db.system.js.

doIt = function() {
innerfunction = function(arg1, arg2) {
db[arg2+"a"].mapReduce(map1, reduce1, {out:
{reduce:tmpCollection}, scope:{"arg1":arg1}})
db[arg2+"b"].mapReduce(map1, reduce1, {out:
{reduce:tmpCollection}, scope:{"arg1":arg2}})

db.tmpCollection.mapReduce(map2, reduce2, {out:
{reduce:arg2+"outCollection"}})
}
innerfunction(4, "collectionOne");
innerfunction(1, "collectionTwo");
// more complicated logic here...
}

I would like to call doIt() on the mongo shell.

When I call doIt() on the mongo shell I get
> ReferenceError: map is not defined (shell)

Note that just calling the following command on the shell works without
the wrapping.
db.collection.mapReduce(map, reduce, {out: {reduce:"outCollection"}})

Is there a command to say "resolve this using the saved function"?
Alternatively, can I fetch the function from db.system.js?

Thanks,
Laura

[Sam Millman]

I am not sure if you understand what system.js is for but stored JS functions are designed to be used within processing so I am not even completly sure how:

db.collection.mapReduce(map, reduce, {out: {reduce:"outCollection"}})

Resolves stored functions as you say since the mongo shell does not understand where to take map and reduce from.

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[Antoine Girbal]

to access any stored function, you need to be executing the code
server side, using eval for example.
Whenever some JS code is executed on client side, any of your stored
code will error as not found.
Executing a mapreduce within an eval is a bad idea, since eval() takes
a write lock for the entire time.
Bottom line:
- dont use eval
- you may not need stored function
- if you need some, they can only be accessed from within code that
executes on server, like within map() or reduce()
AG

[Stanislav Pogrebnyak]

I'v got the same requrements, to call external functions inside map/reduce functions. 

How normally people do that?

Maybe thereis an article about visibility and access for map reduce jobs, and how that area can be altered?

Thanks a lot!

[Sam Millman]

Inside MR functions is simple.

You can actually just call it:

storedFunction();

you can use eval but in this case you don't need to.

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[Antoine Girbal]

store a function server side:
db.system.js.save({_id: "myfunc", value: function(){print("hello");}})

Then call myfunc() in your map/reduce/finalize.

[Stanislav Pogrebnyak]

Thanks for a fast responce, 

Ok, seems like obvious behaviour.