MongoDB Arrays: Using the $push Operator

What is the $push Operator?

$push is an update operator in MongoDB used to append a value to an array field within a document.

If the array field does not exist, $push creates the array and adds the value.

It is commonly used in update operations to modify documents without replacing entire arrays.

• Syntax: { $push: { <field>: <value> } }
• Appends <value> to the array at <field>
• Creates the array if it does not exist

Basic Usage of $push

To add a single element to an array, use $push with the field name and the value to add.

This operation modifies the document in place, preserving existing array elements.

• Example: Add a tag to a blog post's tags array
• db.posts.updateOne({ _id: 1 }, { $push: { tags: "mongodb" } })

Using $push with $each to Add Multiple Elements

The $each modifier allows adding multiple values to an array in a single update.

This is more efficient than multiple $push operations.

• Syntax: { $push: { <field>: { $each: [ <value1>, <value2>, ... ] } } }
• Adds all specified values to the array

Advanced $push Modifiers: $sort and $slice

You can control the order and size of the array after pushing new elements using $sort and $slice modifiers.

$sort orders the array elements ascending (1) or descending (-1).

$slice limits the array to a specified number of elements.

• Example: Keep only top 5 highest scores after pushing new ones
• db.students.updateOne({ _id: 123 }, { $push: { scores: { $each: [88, 95], $sort: -1, $slice: 5 } } })

Best Practices When Using $push

Use $push with $each to minimize the number of update operations.

Combine $sort and $slice to maintain array size and order efficiently.

Avoid pushing large arrays frequently to prevent document growth issues.

• Index array fields if frequently queried.
• Validate array size to avoid exceeding MongoDB document size limits.