MongoDB-评价 db.eval

Question

I have a simple stored script in system.js collection called getAllNotes.

script code: function (x) { return db.notes.find(); } function (x) { return db.notes.find(); }

notes is a collection holding the data I wish to extract.

eval('getAllNotes()') - works well and returns the data.

db.eval('getAllNotes()') - returns a JSON string with various configuration that has nothing to do with my collection See below. Any idea? anyone understands the difference between executing eval and db.eval?

 "_mongo" : {
               "slaveOk" : false,
               "host" : "EMBEDDED"
       },
       "_db" : {
               "_mongo" : {
                       "slaveOk" : false,
                       "host" : "EMBEDDED"
               },
               "_name" : "test"
       },
       "_collection" : {
               "_mongo" : {
                       "slaveOk" : false,
                       "host" : "EMBEDDED"
               },
               "_db" : {
                       "_mongo" : {
                               "slaveOk" : false,
                               "host" : "EMBEDDED"
                       },
                       "_name" : "test"
               },
               "_shortName" : "notes",
               "_fullName" : "test.notes"
       },
       "_ns" : "test.notes",
       "_query" : {

       },
       "_fields" : null,
       "_limit" : 0,
       "_skip" : 0,
       "_batchSize" : 0,
       "_options" : 0,
       "_cursor" : null,
       "_numReturned" : 0,
       "_special" : false

Answer 1

eval takes a string of code that it executes.

db.eval , according to the docs , takes a function to call and a list of parameters to pass to that function. In other words, leave off the single quotes ' here:

db.eval(getAllNotes())

As for the difference between the two, the docs also state it:

The helper db.eval() in the mongo shell wraps the eval command. Therefore, the helper method shares the characteristics and behavior of the underlying command with one exception: db.eval() method does not support the nolock option.

Docs. Important stuff to learn things from before asking other people to do it for you.