3. Creating and Manipulating Documents

Inserting New Documents

Every MongoDB document must have unique _id value. ANd every _id field in a collection must have a unique value from the rest of the documents in the collection. Likewise, you can have a collection where each document is so distinctly different from the other that they don’t have the same shape or any field names in common.

When we insert a new document, MongoDB populates the _id field with a value that is of type ObjectId. The _id doesn’t have to have the type ObjectId. It is just what is created by default to ensure unique values for each document. If you already know of unique value that you can use for each document then you can use those values in the _id field instead.

Inserting One Document At A Time

We can insert a new document using insert.

For example:

db.inspections.insert({
	"_id" : ObjectId("56d61033a378eccde8a8354f"),
	"id" : "10021-2015-ENFO",
	"certificate_number" : 9278806,
	"business_name" : "ATLIXCO DELI GROCERY INC.",
	"date" : "Feb 20 2015",
	"result" : "No Violation Issued",
	"sector" : "Cigarette Retail Dealer - 127",
	"address" : {
		"city" : "RIDGEWOOD",
		"zip" : 11385,
		"street" : "MENAHAN ST",
		"number" : 1712
	}
}
)

The above statemtnt will insert a new document in the inspections collections if the _id is a unique value and there are no errors.

Inserting Multiple Documents At A Time

db.inspections.insert([ 
                        { "test": 1 }, 
                        { "test": 2 }, 
                        { "test": 3 } ])

Updating Documents

• updateOne(): Used to update only one document at one time. If there are multiple documents that match a given criteria, then only one of them will be updated, whichever one the operation finds first. For example: -

  db.zips.updateOne(
    {
        'zip': '12534'
    },
    {
        '$set': {
            'pop': 17630
        }
    }
  )
  

Here, $set is the update operator. In the above query, we are looking to set the pop field to 17630 in the document where zip = 12534. The $set update operator sets the field value to a new specified value. $set syntax also allows us to set multiple fields at the same time by listing the fields and their specified value separated by a comma.

Syntax:

{'$set': 
    {
        'pop': 17630, 
        '<field2>': <new value>,
        ...
    }
}

• updateMany(): Used to update multiple documents at one time. It updates all the documents that match the given criteria. For example: -

  db.zips.updateMany(
                    {'city': 'HUDSON'}, 
                    {'$inc': 
                        {'pop': 10}
                    }
                )
  

Here, $inc is the update operator. In the above query, we are looking to increment the pop field by 10 in every document which lists Hudson as the city. $inc syntax also allows us to update multiple fields at the same time by listing the fields and their increment value separated by a comma.

Syntax:

{'$inc': 
    {
        'pop': 10, 
        '<field2>': <increment value>,
        ...
    }
}

Just like the $set and $incoperator, the $push is also an Update operator. To add an element to an array field, one of the options is to use the $push oeprator which has the following syntax:

Syntax:

{'$push': 
    {
        <field1>: <value1>,
        ....
    }
}

Just like with the set operator, if the field that you specify doesn’t exist in the document then $push will add an array field to the document with a specified value.

Example:

db.grades.updateOne(
    { "student_id": 250, 
    "class_id": 339 },
    { "$push": 
        { "scores": 
            { "type": "extra credit",
                "score": 100 
            }
        }
    }
)

The above query modifies the scores array of the student with student_id=250 by adding another element to it. In this case, the added element is a document with two field value pairs, type-extra credit and score-100.

Deleting Documents and Collections

• deleteOne(): Deletes one document at a time.
• deleteMany(): Deletes many documents at a time.

To delete a collection use db.<collection>.drop. {. prompt-info}