$each modifier with $push in MongoDB - Step-by-Step Execution

Concept Flow - $each modifier with $push

Start with document

↓

$push with $each detected

↓

Iterate over each element in array

↓

Add element to target array field

↓

Update document with new array

↓

End with updated document

This flow shows how MongoDB uses $push with $each to add multiple elements to an array field one by one.

Execution Sample

MongoDB

db.collection.updateOne(
  { _id: 1 },
  { $push: { scores: { $each: [85, 90, 95] } } }
)

Adds multiple scores (85, 90, 95) to the 'scores' array in the document with _id 1.

Execution Table

Step	Action	Current 'scores' array	Element Added	Resulting 'scores' array
1	Start update	[80, 82]	N/A	[80, 82]
2	Push 85	[80, 82]	85	[80, 82, 85]
3	Push 90	[80, 82, 85]	90	[80, 82, 85, 90]
4	Push 95	[80, 82, 85, 90]	95	[80, 82, 85, 90, 95]
5	Update complete	[80, 82, 85, 90, 95]	N/A	[80, 82, 85, 90, 95]

💡 All elements in $each array pushed; update operation finished.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
scores	[80, 82]	[80, 82, 85]	[80, 82, 85, 90]	[80, 82, 85, 90, 95]	[80, 82, 85, 90, 95]

Key Moments - 2 Insights

Why does $push need $each to add multiple elements?

Without $each, $push adds only one element. The execution_table shows each element added step-by-step using $each (rows 2-4).

Does $push with $each replace the array or add to it?

It adds elements to the existing array, not replace it. See how 'scores' grows after each step in variable_tracker.

Visual Quiz - 3 Questions

Look at the execution_table, what is the 'scores' array after step 3?

A [80, 82, 85]

B [80, 82, 85, 90]

C [85, 90]

D [80, 82]

💡 Hint

Check the 'Resulting scores array' column at step 3 in execution_table.

At which step does the last element get added to the array?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the 'Element Added' column in execution_table to find when 95 is added.

If we remove $each and try to push [85, 90, 95] directly, what happens?

A Each element is added separately automatically

B Update fails with error

C The entire array [85, 90, 95] is added as one element

D Nothing changes in the array

💡 Hint

Recall that $push without $each adds one element; here that element would be the whole array.

Concept Snapshot

$push with $each lets you add multiple elements to an array field.
Syntax: {$push: {field: {$each: [val1, val2, ...]}}}
Without $each, $push adds only one element.
Each element is appended in order.
Useful for batch updates to arrays.

Full Transcript

This visual execution shows how MongoDB's $push operator combined with $each modifier adds multiple elements to an array field in a document. Starting with an array [80, 82], each element from [85, 90, 95] is added one by one, updating the array step-by-step until it becomes [80, 82, 85, 90, 95]. The $each modifier is necessary to push multiple elements; without it, $push would add the entire array as a single element. The execution table and variable tracker clearly show the array's state after each addition, helping beginners understand the incremental update process.