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$min

Definition

$min

The $min updates the value of the field to a specified value if the specified value is less than the current value of the field. The $min operator can compare values of different types, using the BSON comparison order.

{ $min: { <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 $min operator sets the field to the specified value.

For comparisons between values of different types, such as a number and a null, $min uses the BSON comparison order.

Examples

Use $min to Compare Numbers

Consider the following document in the collection scores:

{ _id: 1, highScore: 800, lowScore: 200 }

The lowScore for the document currently has the value 200. The following operation uses $min to compare 200 to the specified value 150 and updates the value of lowScore to 150 since 150 is less than 200:

db.scores.update( { _id: 1 }, { $min: { lowScore: 150 } } )

The scores collection now contains the following modified document:

{ _id: 1, highScore: 800, lowScore: 150 }

The next operation has no effect since the current value of the field lowScore, i.e 150, is less than 250:

db.scores.update( { _id: 1 }, { $min: { lowScore: 250 } } )

The document remains unchanged in the scores collection:

{ _id: 1, highScore: 800, lowScore: 150 }

Use $min to Compare Dates

Consider the following document in the collection tags:

{
  _id: 1,
  desc: "crafts",
  dateEntered: ISODate("2013-10-01T05:00:00Z"),
  dateExpired: ISODate("2013-10-01T16:38:16Z")
}

The following operation compares the current value of the dateEntered field, i.e. ISODate("2013-10-01T05:00:00Z"), with the specified date new Date("2013-09-25") to determine whether to update the field:

db.tags.update(
   { _id: 1 },
   { $min: { dateEntered: new Date("2013-09-25") } }
)

The operation updates the dateEntered field:

{
  _id: 1,
  desc: "crafts",
  dateEntered: ISODate("2013-09-25T00:00:00Z"),
  dateExpired: ISODate("2013-10-01T16:38:16Z")
}
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