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Cursor Methods

cursor.max()

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  • Definition
  • Behavior
  • Example

Definition

cursor.max()

Important

mongosh Method

This page documents a mongosh method. This is not the documentation for a language-specific driver, such as Node.js.

For MongoDB API drivers, refer to the language-specific MongoDB driver documentation.

Specifies the exclusive upper bound for a specific index in order to constrain the results of find(). max() provides a way to specify an upper bound on compound key indexes.

Parameters

The max() method has the following parameter:

Parameter
Type
Description
indexBounds
document
The exclusive upper bound for the index keys.

The indexBounds parameter has the following prototype form:

{ field1: <max value>, field2: <max value2> ... fieldN:<max valueN> }

The fields correspond to all the keys of a particular index in order.

Note

Index Use

To use an index with the max() method, you must use the hint() method to specify the index you want to use, exept when the find() query is an equality condition on the _id field.

Tip

See also:

min()

max() exists primarily to support the mongos (sharding) process.

Behavior

Interaction with Index Selection

Because max() requires an index on a field, and forces the query to use this index, you may prefer the $lt operator for the query if possible. Consider the following example:

db.products.find( { _id: { $in: [ 6, 7 ] } } ).max( { price: NumberDecimal("1.39") } ).hint( { price: 1 } )

The query will use the index on the price field, even if the index on _id may be better.

Index Bounds

If you use max() with min() to specify a range:

  • the index bounds specified in min() and max() must both refer to the keys of the same index.

  • the bound specified by max() must be greater than the bound specified by min().

max() without min()

The min() and max() methods indicate that the system should avoid normal query planning. They construct an index scan where the index bounds are explicitly specified by the values given in min() and max().

Warning

If one of the two boundaries is not specified, the query plan will be an index scan that is unbounded on one side. This may degrade performance compared to a query containing neither operator, or one that uses both operators to more tightly constrain the index scan.

Example

Note

Starting in MongoDB 4.2, you must explicitly specify the particular index with the hint() method to run max() with the following exception: you do not need to hint if the find() query is an equality condition on the _id field { _id: <value> }.

For the examples below, create a sample collection named products that holds the following documents:

db.products.insertMany([
   { "_id" : 1, "item" : "apple", "type" : "honey crisp", "price" : NumberDecimal("1.99") },
   { "_id" : 2, "item" : "apple", "type" : "fuji", "price" : NumberDecimal("1.99") },
   { "_id" : 3, "item" : "apple", "type" : "jonagold", "price" : NumberDecimal("1.29") },
   { "_id" : 4, "item" : "apple", "type" : "jonathan", "price" : NumberDecimal("1.29") },
   { "_id" : 5, "item" : "apple", "type" : "mcintosh", "price" : NumberDecimal("1.29") },
   { "_id" : 6, "item" : "apple", "type" : "cortland", "price" : NumberDecimal("1.29") },
   { "_id" : 7, "item" : "orange", "type" : "cara cara", "price" : NumberDecimal("2.99") },
   { "_id" : 9, "item" : "orange", "type" : "satsuma", "price" : NumberDecimal("1.99") },
   { "_id" : 8, "item" : "orange", "type" : "valencia", "price" : NumberDecimal("0.99") },
   { "_id" : 10, "item" : "orange", "type" : "navel", "price" : NumberDecimal("1.39") }
])

Create the following indexes for the collection:

db.products.createIndexes( [
   { "item" : 1, "type" : 1 },
   { "item" : 1, "type" : -1 },
   { "price" : 1 }
] )

  • Using the ordering of { item: 1, type: 1 } index, max() limits the query to the documents that are below the bound of item equal to apple and type equal to jonagold:

    db.products.find().max( { item: 'apple', type: 'jonagold' } ).hint( { item: 1, type: 1 } )

    The query returns the following documents:

    { "_id" : 6, "item" : "apple", "type" : "cortland", "price" : NumberDecimal("1.29") }
    { "_id" : 2, "item" : "apple", "type" : "fuji", "price" : NumberDecimal("1.99") }
    { "_id" : 1, "item" : "apple", "type" : "honey crisp", "price" : NumberDecimal("1.99") }

  • Using the ordering of the index { price: 1 }, max() limits the query to the documents that are below the index key bound of price equal to NumberDecimal("1.99") and min() limits the query to the documents that are at or above the index key bound of price equal to NumberDecimal("1.39"):

    Note

    The bound specified by max() must be greater than the bound specified by min().

    db.products.find().min( { price: NumberDecimal("1.39") } ).max( { price:  NumberDecimal("1.99") } ).hint( { price: 1 } )

    The query returns the following documents:

    { "_id" : 10, "item" : "orange", "type" : "navel", "price" : NumberDecimal("1.39") }

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cursor.map()