20.4.3.4 Modify Documents

The modify() method works by filtering a collection to include only the documents to be modified and then applying the operations that you specify to those documents.

In the following example, the modify() method uses the search condition to identify the document to change and then the set() method replaces two values within the nested demographics object.

mysql-py> db.countryinfo.modify("_id = 'SEA'").\
set("demographics", {"LifeExpectancy": 78, "Population": 28})
Query OK, 1 item affected (0.04 sec)

After you modify a document, use the find() method to verify the change.

To remove content from a document, use the modify() and unset() methods. For example, the following query removes the GNP from a document that matches the search condition.

mysql-py> db.countryinfo.modify("Name = 'Sealand'").unset("GNP")
Query OK, 1 item affected (0.01 sec)

Use the find() method to verify the change.

mysql-py> db.countryinfo.find("Name = 'Sealand'")
[
    {
        "IndepYear": 1967,
        "Name": "Sealand",
        "_id": "SEA",
        "demographics": {
            "LifeExpectancy": 78,
            "Population": 28
        },
        "geography": {
            "Continent": "Europe",
            "Region": "British Islands",
            "SurfaceArea": 193
        },
        "government": {
            "GovernmentForm": "Monarchy",
            "HeadOfState": "Michael Bates"
        }
    }
]
1 document in set (0.00 sec)

To append an element to an array field, or insert, or delete elements in an array, use the array_append(), array_insert(), or array_delete() methods. The following examples modify the countryinfo collection to enable tracking of international airports.

The first example uses the modify() and set() methods to create a new Airports field in all documents.

mysql-py> db.countryinfo.modify(True).set("Airports", [])
Query OK, 240 items affected (0.07 sec)

With the Airports field added, the next example uses the array_append() method to add a new airport to one of the documents. $.Airports in the following example represents the Airports field of the current document.

mysql-py> db.countryinfo.modify("Name = 'France'").array_append("$.Airports", "ORY")
Query OK, 1 item affected (0.02 sec)

Use db.countryinfo.find("Name = 'France'") to see the change.

To insert an element at a different position in the array, use the array_insert() method to specify which index to insert in the path expression. In this case, the index is 0, or the first element in the array.

mysql-py> db.countryinfo.modify("Name = 'France'").array_insert("$.Airports[0]", "CDG")
Query OK, 1 item affected (0.04 sec)

To delete an element from the array, you must pass to the array_delete() method the index of the element to be deleted.

mysql-py> db.countryinfo.modify("Name = 'France'").array_delete("$.Airports[1]")
Query OK, 1 item affected (0.03 sec)