Change the type of a MongoDB field to integer from its console

Question

We have an application that stores some configuration values from C/C++ in MongoDB and has the capability to be restarted (i.e. it runs for a while, someone interrupts the application, changes the configuration, then runs the app again, and it picks up where it left off). This works like a charm for boolean and string configurations.

But then we have some integers (in our current C/C++ implementation - 32 bit values). And when I use the MongoDB console to modify those integer values, Mongo always stores them back as Number (which is doulble in the C/C++ implementation). We will change the app to take double values where it expects integers but I was wondering if there is a way to force Mongo to store integers from its JavaScript console.

Any suggestions?

Resave the values as using parseFloat() or just don't put any speech marks around the value — Sammaye, Jul 01 '12 at 11:06

score 9 · Accepted Answer · edited May 23 '17 at 12:34

9

In the C/C++ "sense of the word", ints are not actually guaranteed to be 32-bit values. An int must be at least 16-bits, but generally matches the platform architecture (eg. 32 or 64bit).

As mentioned by @Jasd, JavaScript does only have one numeric type which is a floating point (double in C).

From the MongoDB shell you should be able to use the functions NumberInt(..) to get a BSON 32-bit integer value or NumberLong(..) to get a BSON 64-bit integer.

edited May 23 '17 at 12:34

Community

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answered Jul 01 '12 at 21:27

Stennie

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nice catch about the int size! – Георги Кременлиев Jul 02 '12 at 11:06

Nic Cottrell · Answer 2 · 2014-02-25T15:23:19.183

9

You can fix the types of all values for a certain field on the console with something like:

db.Statistic.find({kodoId: {$exists: true}}).forEach(function (x) {
  x.kodoId = NumberInt(x.kodoId);
  db.Statistic.save(x);
});

This will only load documents that have the kodoId field and convert them to int and resave. You could do something like:

db.Statistic.find({kodoId: {$exists: true}}, {kodoId: 1}).forEach(function (x) {
   db.Statistic.update({ _id: x._id },
      {$set: {
        kodoId: NumberInt(x.kodoId)
      }});
});

with a second param which will only load the kodoId value (hopefully from an index). This should be much quicker since it doesn't need to load and resave the entire document - just that one field.

edited Feb 25 '14 at 15:23

answered Feb 25 '14 at 14:00

Nic Cottrell

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You might was to add a `try .. catch (err)` around the 2nd example in case there are some values which are already NumberInt since it will throw an error. – Nic Cottrell Feb 25 '14 at 14:04
Worked like a charm for me. Thanks! – Mika Andrianarijaona Nov 02 '15 at 08:23
I came back to this answer more than I llike to admit... – Nicolas Martinez Oct 30 '20 at 15:53
Only one observation, do NOT mix first and second solutions! I have done that, projecting the field but calling save instead of set... awful mess – Nicolas Martinez Oct 30 '20 at 15:58

score 0 · Answer 3 · answered Jul 01 '12 at 11:29

MongoDB's shell is powered by a JavaScript Engine. And JavaScript has no type for integer. It knows only Number, which is a type for floating-point numbers.
You can try using the MongoDB type NumberLong, but it didn't work out for me when i once had the same problem.

Change the type of a MongoDB field to integer from its console

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