MongoDB v4.2 Update Operators – Part II

Already we have seen that the Field Update Operators in previous blog.

In this blog we can seen about Array and Bitwise Operators and it’s explanation.

Array Update Operators :

1.) $ :

To update the first element that matches the query condition.

Syntax :

{ "<array.$>" : value }

Explanation :

• The Array field must appear as part of the query document.

2.) $ [ ] :

To update all elements in an array for the document that matches the query condition.

Syntax :

{ < update operator > : { "<array>.$[]" : value } } 

Explanation :

• The query must include an exact equality match on the array field in order to use the $[ ] positional operator in the update statement.

3.) $ [ <identifier> ] :

To update all elements that match the array filter condition for the document that matches the query condition.

Syntax :

{ < update operator > : { " <array>.$[ identifier ] " : value } } , { arrayFilters : [ { <identifier> : <condition> } ] }

Explanation :

• The <identifier> must begin with lowercase letter and contain only alphanumeric characters.

4.) $addToSet :

Adds elements to an array only if they don’t already exist in the set.

Syntax :

{ $addToSet : { <field1> : <value> , ..} }

Explanation :

• $addToSet only ensures that there are no duplicates items added to the set and does not affect existing duplicate elements.
• $addToSet does not guarantee a particular ordering of elements in the modified set.

5.) $pop :

Removes the first or last item of an array.

Syntax :

{ $pop : { <field> : < -1 | 1 > , ...} }

Explanation :

• The $pop operation fails if the <field> is not an array.
• If the $pop operator removes the last item in the <field>, the <field> will then hold an empty array.

6.) $pull :

Removes all elements that match a specified query.

Syntax :

{ $pull : { <field1> : < value | condition > , <field2> : < value | condition > , ... } }

Explanation :

• If the specified <value> to remove is an array, $pull removes only the elements in the array that match the specified <value> exactly,including order.
• If the specified <value> to remove is a document, $pull removes only the elements in the array that have the exact same fields and values, the ordering of the field can differ.

7.) $push :

Adds an item to an array.

Syntax :

{ $push : { <field> : <value> , ... } } 

Explanation :

• The $push operator appends a specified value to an array.
• If the field is absent in the document to update, $push adds the array field with the value as its element.
• If the field is not an array, the operation will fail.

8.) $pullAll :

Removes all matching values from an array.

Syntax :

{ $pullAll : { <field1> : [ <value1> , <value2> , ... ] , ... } }

Explanation :

• If a <value> to remove is a document or an array, $pullAll removes only the elements in the array that match the specified <value> exactly,including order.

9.) $each :

Modifies the $push and $addToSet operators to append multiple items for array updates.

Syntax :

{ $addToSet : { <field> : { $each : [ <value1> , <value2> ... ] } } }

{ $push : { <field> : { $each : [ <value1> , <value2> ... ] } } }

Explanation :

• Use with the $addToSet operator to add multiple values to an array <field> if the values do not exist in the <field>.
• Use with the $push operator to append multiple values to an array <field>.

10.) $position :

Modified the $push operator to specify the position in the array to add elements.

Syntax :

{ $push : { <field> : { $each : [ <value1> , <value2> , ... ] , $position : <num> } } }

Explanation :

• The $position modifier specifies the location in the array at which the $push operator inserts elements.
• Without the $position modifier, the $push operator inserts elements to the end of the array.

11.) $slice :

Modifies the $push operator to limit the size of updated arrays.

Syntax :

{ $push : { <field> : { $each : [ <value1> , <value2> , ... ] , $slice : <num> } } }

Explanation :

• Use the $slice modifier, it must appear with the $each modifier, we can pass an empty array [ ] to the $each modifier such that only the $slice modifier has an effect.

12.) $sort :

Modifies the $push operator to reorder documents stored in an array.

Syntax :

{ $push :  { <field> : { $each : [ <value1> , <value2> , ... ] , $sort : <sort specification> } } } 

Explanation :

• The $sort modifier orders the elements of an array during a $push operation.
• To sort array elements that are not documents, or if the array elements are documents, to sort by the whole documents, specify 1 for ascending or -1 for descending.

Bitwise Update Operator :

1.) $bit :

It performs bitwise AND,OR and XOR updates of integer values.

Syntax :

{ $bit : { <field> : { <and | or | xor > : <int> } } }

Explanation :

• Only use this operator with integer fields ( either 32-bit integer or 64-bit integer ).
• The $bit operator performs a bitwise update of a field.

In this blog I have covered remaining update operators.