Mongo DB查询数组中的对象

https://docs.mongodb.com/manual/tutorial/query-array-of-documents/

db.inventory.insertMany( [
   {
      item: "journal", instock: [ {
      warehouse: "A", qty: 5 }, {
      warehouse: "C", qty: 15 } ] },
   {
      item: "notebook", instock: [ {
      warehouse: "C", qty: 5 } ] },
   {
      item: "paper", instock: [ {
      warehouse: "A", qty: 60 }, {
      warehouse: "B", qty: 15 } ] },
   {
      item: "planner", instock: [ {
      warehouse: "A", qty: 40 }, {
      warehouse: "B", qty: 5 } ] },
   {
      item: "postcard", instock: [ {
      warehouse: "B", qty: 15 }, {
      warehouse: "C", qty: 35 } ] }
]);

Equality matches on the whole embedded/nested document require an exact match of the specified document, including the field order. For example, the following query does not match any documents in the inventory collection:

db.inventory.find( {
      "instock": {
      qty: 5, warehouse: "A" } } )