Filter subdocuments by conditions in Mongo Charts Query

[Fryderyk_Chopin]

Hi,

I want to filter subdocuments in Mongo Charts Query.

I have a document with a field and a field of array of documents like:

{
   'n': 1,
   subdocuments_array: [sub_1, sub_2,...,sub_n],
},
{
   'n':2,
   subdocuments_array:[sub_1, sub_2,...,sub_n],
} 

and so on.

These sub_n have the following form:

{
   'value': some number
   'flag1': 0 or 1,
   'flag2': 0 or 1
}

I want to use only the subdocuments with flag1 and flag 2 equal to 1.

I’ve tried to use {'sub_n.flag': {$ne: 0}} but this is filtering the entire document when there is a subdocument with flag equal to 0.

I hope you can help me.

Thank you.

[tomhollander]

Hi @Fryderyk_Chopin -

The trick here is to use $unwind on the array before you filter. That will result in a new document being created for each array element, which you can then filter with a $match stage.

Based on your sample docs, the full pipeline would be something like:

[
  { $unwind: "$subdocuments_array" },
  { $match: { "subdocuments_array.flag1":1, "subdocuments_array.flag2":1 } }
]