Querying an array of arrays in MongoDB?

Use $in operator to query an array of arrays in MongoDB. To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −

> db.arrayOfArraysDemo.insertOne({"EmployeeName":"Larry","EmployeeSkills":[["Java","MongoDB","MySQL","SQL Server"]]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c7f7a8d8d10a061296a3c5b")
}
> db.arrayOfArraysDemo.insertOne({"EmployeeName":"Mike","EmployeeSkills":[["C","C++"]]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c7f7aa68d10a061296a3c5c")
}

Display all documents from a collection with the help of find() method. The query is as follows −

> db.arrayOfArraysDemo.find().pretty();

The following is the output −

{
   "_id" : ObjectId("5c7f7a8d8d10a061296a3c5b"),
   "EmployeeName" : "Larry",
   "EmployeeSkills" : [
      [
         "Java",
         "MongoDB",
         "MySQL",
         "SQL Server"
      ]
   ]
}
{
   "_id" : ObjectId("5c7f7aa68d10a061296a3c5c"),
   "EmployeeName" : "Mike",
   "EmployeeSkills" : [
      [
         "C",
         "C++"
      ]
   ]
}

Here is the query for querying an array of arrays in MongoDB −

> db.arrayOfArraysDemo.find({'EmployeeSkills':{$elemMatch:{$elemMatch:{$in:['MongoDB']}}}
}).pretty();

The following is the output −

{
   "_id" : ObjectId("5c7f7a8d8d10a061296a3c5b"),
   "EmployeeName" : "Larry",
   "EmployeeSkills" : [
      [
         "Java",
         "MongoDB",
         "MySQL",
         "SQL Server"
      ]
   ]
}