- Reference >
- Operators >
- Update Operators >
- Field Update Operators >
- $max
$max¶
On this page
Definition¶
- $max¶
The $max operator updates the value of the field to a specified value if the specified value is greater than the current value of the field. The $max operator can compare values of different types, using the BSON comparison order.
The $max operator expression has the form:
{ $max: { <field1>: <value1>, ... } }
To specify a <field> in an embedded document or in an array, use dot notation.
Behavior¶
If the field does not exists, the $max operator sets the field to the specified value.
Examples¶
Use $max to Compare Numbers¶
Consider the following document in the collection scores:
{ _id: 1, highScore: 800, lowScore: 200 }
The highScore for the document currently has the value 800. The following operation uses $max to compare the 800 and the specified value 950 and updates the value of highScore to 950 since 950 is greater than 800:
db.scores.update( { _id: 1 }, { $max: { highScore: 950 } } )
The scores collection now contains the following modified document:
{ _id: 1, highScore: 950, lowScore: 200 }
The next operation has no effect since the current value of the field highScore, i.e. 950, is greater than 870:
db.scores.update( { _id: 1 }, { $max: { highScore: 870 } } )
The document remains unchanged in the scores collection:
{ _id: 1, highScore: 950, lowScore: 200 }
Use $max to Compare Dates¶
Consider the following document in the collection tags:
{
_id: 1,
desc: "crafts",
dateEntered: ISODate("2013-10-01T05:00:00Z"),
dateExpired: ISODate("2013-10-01T16:38:16.163Z")
}
The following operation compares the current value of the dateExpired field, i.e. ISODate("2013-10-01T16:38:16.163Z"), with the specified date new Date("2013-09-30") to determine whether to update the field:
db.tags.update(
{ _id: 1 },
{ $max: { dateExpired: new Date("2013-09-30") } }
)
The operation does not update the dateExpired field:
{
_id: 1,
desc: "decorative arts",
dateEntered: ISODate("2013-10-01T05:00:00Z"),
dateExpired: ISODate("2013-10-01T16:38:16.163Z")
}
Thank you for your feedback!
We're sorry! You can Report a Problem to help us improve this page.