Example for elemMatch

Find all documents against array fields which matches any of the input

Suppose, I have a collection "StockUsers" like this.

{
    "user":"kiran",
    "stocksPurchased":["hdfc","sbi","icici"]
}

{
    "user":"vanaja",
    "stocksPurchased":["hdfc","idbi","pnb"]
}

{
    "user":"karthika",
    "stocksPurchased":["idfc","idbi"]
}

{
    "user":"venkat",
    "stocksPurchased":["citi"]
}


Now, If i want to query the users who purchased any of the given stocks.

Ex: Retrieve all users who purchased idfc or pnb

Query:

db.StockUsers.aggregate([
{
   "$match": {
       "stocksPurchased": {"$elemMatch":{"$in":["idfc","pnb"]}}
   }
}
])

Response:

{
    "user":"vanaja",
    "stocksPurchased":["hdfc","idbi","pnb"]
}

{
    "user":"karthika",
    "stocksPurchased":["idfc","idbi"]
}

Conclusion

Use elemMatch to query on array fields to which matches on ANY given input.