Select tags of product collection in MongoDB?

Question

I am new user of MongoDB and I use mongoDB with php.
This is my structure:

{
 "_id" : ObjectId("**********cd940c0f000029"),
 "product_name" : "HP",
 "product_description" : "Test",
 "product_brand" : "HP",
 "product_category" : "NoteBook",
 "product_tags" : [ 
   "HP", 
   "corei5"
 ]
}

Now I want to select all product tags in this collection. Please guide me to do this job.

Answer 1

$unwind (aggregation)

Definition

$unwind
Deconstructs an array field from the input documents to output a document for each element. Each output document is the input document with the value of the array field replaced by the element.

The $unwind stage has one of two syntaxes:

The operand is a field path:

{ $unwind: <field path> }

To specify a field path, prefix the field name with a dollar sign $ and enclose in quotes.
The operand is a document:

New in version 3.2.

{
  $unwind:
    {
      path: <field path>,
      includeArrayIndex: <string>,
      preserveNullAndEmptyArrays: <boolean>
    }
 }

For Continuous!