doEval() With Multiline String Argument

Question

Using Groovy 2.3.6, GMongo 1.2, Java 1.8, MongoDB 3.0.0...

I'm trying to use doEval() to get a count of documents in a collection. (For various reasons I want to use doEval() rather than count()). Invoking doEval() with a single line string argument returns retval with a double value of 1.0 and ok with a double value of 1.0 which is what I expect:

def str = "db.configurations.count({name: 'Mike'})"
database.doEval(str)

If the argument is on multiple lines retval that is returned is null (ok is 1.0).

def str = "db.configurations.count({\nname: 'Mike'\n})"
database.doEval(str)

I expect doEval to return a retval of 1.0 not null, like in the first example. Is this a bug or is my expectation incorrect? Should doEval() support a multiline string argument?

score 1 · Accepted Answer · answered Apr 20 '15 at 11:10

From doEval() javadoc:

Evaluates JavaScript functions on the database server. This is useful if you need to touch a lot of data lightly, in which case network transfer could be a bottleneck.

Parameters:

code - String representation of JavaScript function

args - arguments to pass to the JavaScript function

So you are not passing a javascript function to doEvalmethod. Anyway, the result you are getting is consistent with the result you can get invoking directly the mongo shell:

> db.eval("db.configurations.count({name: 'Mike'})");
1
> db.eval("db.configurations.count({\nname: 'Mike'\n})");
null

(I did not dig deeper on mongo shell javascript internals... :-)

Passing a javascript function you can get the result you want:

println db.configurations.count([name: 'Mike'])

def str = '''function(name) {
    return db.configurations.count({
        name: name
    });
}'''
println db.doEval(str, 'Mike')

The above yields:

1
[serverUsed:/127.0.0.1:27017, retval:1.0, ok:1.0]

doEval() With Multiline String Argument

1 Answers1