Database Manual / Reference / mongosh Methods / Cursors

cursor.max() (mongosh method方法)

Definition定义

cursor.max()

Important

mongosh Method方法

This page documents a mongosh method. This is not the documentation for a language-specific driver, such as Node.js.本页记录了一种mongosh方法。这不是针对特定语言驱动程序（如Node.js）的文档。

For MongoDB API drivers, refer to the language-specific MongoDB driver documentation.有关MongoDB API驱动程序，请参阅特定语言的MongoDB驱动程序文档。

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.指定特定索引的独占上限，以约束find()的结果。max()提供了一种指定复合键索引上限的方法。

Parameters参数

The max() method has the following parameter:max()方法有以下参数：

Parameter参数Type类型Description描述
indexBoundsdocument文档The exclusive upper bound for the index keys.索引键的唯一上限。

The indexBounds parameter has the following prototype form:indexBounds参数具有以下原型形式：

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

The fields correspond to all the keys of a particular index in order.这些字段按顺序对应于特定索引的所有键。

Note

Index Use索引使用

To use an index with the max() method, you must use the hint() method to specify the index you want to use, except when the find() query is an equality condition on the _id field.要使用带有max()方法的索引，必须使用hint()方法指定要使用的索引，除非find()查询是_id字段上的相等条件。

Tip

min()

max() exists primarily to support the mongos (sharding) process.max()的存在主要是为了支持mongos（分片）过程。

Compatibility兼容性

This method is available in deployments hosted in the following environments:此方法在以下环境中托管的部署中可用：

  • MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud：云中MongoDB部署的完全托管服务

Note

This command is supported in all MongoDB Atlas clusters. 所有MongoDB Atlas集群都支持此命令。For information on Atlas support for all commands, see Unsupported Commands.有关Atlas支持所有命令的信息，请参阅不支持的命令。

  • MongoDB Enterprise: The subscription-based, self-managed version of MongoDB：MongoDB的基于订阅的自我管理版本
  • MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB：MongoDB的源代码可用、免费使用和自我管理版本

Behavior行为

Interaction with Index Selection与指数选择的互动

Because max() requires an index on a field, and forces the query to use this index, you may prefer the $lt operator for the query if possible. Consider the following example:因为max()需要字段上的索引，并强制查询使用此索引，如果可能的话，您可能更喜欢查询的$lt运算符。考虑以下示例：

db.products.find( { _id: { $in: [ 6, 7 ] } } ).max( { price: Decimal128("1.39") } ).hint( { price: 1 } )

The query will use the index on the price field, even if the index on _id may be better.查询将使用price字段上的索引，即使_id上的索引可能更好。

Index Bounds索引边界

If you use max() with min() to specify a range:如果你使用max()和min()来指定一个范围：

  • the index bounds specified in min() and max() must both refer to the keys of the same index.min()和max()中指定的索引边界必须都引用同一索引的键。
  • the bound specified by max() must be greater than the bound specified by min().max()所指定的界限必须大于min()所定义的界限。

max() without min()max()不带min()

The min() and max() methods indicate that the system should avoid normal query planning. min()和max()方法表明系统应避免正常的查询计划。They construct an index scan where the index bounds are explicitly specified by the values given in min() and max().它们构造了一个索引扫描，其中索引边界由min()和max()中给出的值显式指定。

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.如果未指定两个边界中的一个，则查询计划将是一侧无边界的索引扫描。与既不包含运算符也不使用两个运算符来更严格地约束索引扫描的查询相比，这可能会降低性能。

Example示例

Note

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> }.您必须使用hint()方法显式指定特定索引才能运行max()，但有以下例外：如果find()查询是_id字段{ _id: <value> }上的相等条件，则不需要提示。

For the examples below, create a sample collection named products that holds the following documents:对于以下示例，创建一个名为products的示例集合，其中包含以下文档：

db.products.insertMany([
   { "_id" : 1, "item" : "apple", "type" : "honey crisp", "price" : Decimal128("1.99") },
   { "_id" : 2, "item" : "apple", "type" : "fuji", "price" : Decimal128("1.99") },
   { "_id" : 3, "item" : "apple", "type" : "jonagold", "price" : Decimal128("1.29") },
   { "_id" : 4, "item" : "apple", "type" : "jonathan", "price" : Decimal128("1.29") },
   { "_id" : 5, "item" : "apple", "type" : "mcintosh", "price" : Decimal128("1.29") },
   { "_id" : 6, "item" : "apple", "type" : "cortland", "price" : Decimal128("1.29") },
   { "_id" : 7, "item" : "orange", "type" : "cara cara", "price" : Decimal128("2.99") },
   { "_id" : 9, "item" : "orange", "type" : "satsuma", "price" : Decimal128("1.99") },
   { "_id" : 8, "item" : "orange", "type" : "valencia", "price" : Decimal128("0.99") },
   { "_id" : 10, "item" : "orange", "type" : "navel", "price" : Decimal128("1.39") }
])

Create the following indexes for the collection:为集合创建以下索引：

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:使用{ item: 1, type: 1 }索引的顺序，max()将查询限制在item等于apple和type等于jonagold的界限以下的文档：

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

    The query returns the following documents:查询返回以下文档：

    { "_id" : 6, "item" : "apple", "type" : "cortland", "price" : Decimal128("1.29") }
    { "_id" : 2, "item" : "apple", "type" : "fuji", "price" : Decimal128("1.99") }
    { "_id" : 1, "item" : "apple", "type" : "honey crisp", "price" : Decimal128("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 Decimal128("1.99") and min() limits the query to the documents that are at or above the index key bound of price equal to Decimal128("1.39"):使用索引{ price: 1 }的顺序，max()将查询限制在price等于Decimal128("1.39")的索引键界限以下的文档中，min()将搜索限制在price大于等于Decimal128("1.39")索引键界限的文档中：

    Note

    The bound specified by max() must be greater than the bound specified by min().max()所指定的界限必须大于min()所定义的界限。

    db.products.find().min( { price: Decimal128("1.39") } ).max( { price:  Decimal128("1.99") } ).hint( { price: 1 } )

    The query returns the following documents:查询返回以下文档：

    { "_id" : 10, "item" : "orange", "type" : "navel", "price" : Decimal128("1.39") }