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- $max
$max¶
- $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. If the field does not exists, the $max operator sets the field to the specified value. The $max operator can compare values of different types, using the BSON comparison order.
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")
}