data type converstion in DocumentDB using aggregation pipelines

Question

I have a MongoDB aggregation pipeline that converts a string to a double.  I just realized that DocumentDB doesn't support the `$convert` or `$toDouble` operators.  Is there any workaround for this problem while still using an aggregation pipeline?

Below is an extract from my pipeline that works in MongoDB Atlas:

```
...
{
    $convert:{
        input:$subDoc.stringVar,
        to:'double',
        'onError':0,
        'onNull':0
    }
}, 
...
```

Answer

Hello. You could use the Javascript parseFloat() method and programmatically update those strings to double in the existing collection.  Or use an $out stage in the aggregation and update the results afterwards.
Something like this will loop through all documents in the collection and update the string:

```
db.collection.find({}).forEach( function(doc) {
  doc.subDoc.stringVar = parseFloat( doc.subDoc.stringVar );
  db.collection.update( { _id: doc._id }, {$set: { "subDoc.stringVar": doc.subDoc.stringVar } } )
 });
```

data type converstion in DocumentDB using aggregation pipelines

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