Database
[{contacts:["test"],/**_id: ObjectId("614a1301a926d73628d791fe"),*/username:"erick",socketId:"OB8uqmHnsGPKC3gcAAAB"},{contacts:[{contacts:["test2"],/** _id: ObjectId("614a1301a926d73628d791fe"),*/username:"erick",socketId:"OB8uqmHnsGPKC3gcAAAB"}],/** _id: ObjectId("614a1306a926d73628d79204"),*/username:"tachancka",socketId:"cN333_zn8r48K_0tAAAB"}]
Query
db.collection.find({username:"tachancka","contacts.username":"erick"})