Mongo: Query to get count of objects in a nested field.

[Karan]

Hello Everyone,

I needed some help to create a count query on nested objects in a field, across all documents. Each document json has a many fields. One particular field called "hotlinks" comprises of many internal dynamic object fields.

Doc1:

{

  hotlinks : { 112222:{....} , 333333: {.....} , 545555: {.....}      }

}

Doc2:

{

  hotlinks : { 67756:{....} , 756767: {.....} , 1111111: {.....}      }

}

Each document has a hotlinks fields. The hotlinks field comprises of varied inner hotlink objects. Each key is a java unique id and has objects that contain data (inner fields)

I needed a way to get the count of all the inner nested objects of the field – ‘hotlinks’.

For example the summation of inner objects of hotlinks in doc1 and doc2 would be 6.

Is there any way to do this via a single query to get the count across all documents.

Thanks a lot,

Karan

[Gary R]

A few thoughts.

• This would work nicely in the aggregation framework if the 'hotlinks fields" would be elements in an array instead of a document.
• Or, you could easy maintain a counter as hotlinks are added and removed and just read this.
• Or, in map-reduce, javascript could include the idea:  for(k in obj) {count++;}

Gary R.

--------------------------------

[Karan]

Hi Gary,

Thank you so much. All the ideas you gave are great.

For now, i have implemented the second option that you have suggested- Maintain a counter.

This is now working for me.

Thanks so much,

Karan