Compatibility Changes with Legacy mongo Shell与传统mongo Shell的兼容性更改

Read Operations on a Secondary Node辅助节点上的读取操作

When using the legacy mongo shell to connect directly to secondary replica set member, you must run mongo.setReadPref() to enable secondary reads.当使用旧式mongoshell直接连接到secondary副本集成员时，必须运行mongo.setReadPref()才能启用辅助读取。

When using mongosh to connect directly to a secondary replica set member, you can read from that member if you specify a read preference of either:使用mongosh直接连接到secondary副本集成员时，如果指定以下任一读取首选项，则可以从该成员读取：

• primaryPreferred
• secondary
• secondaryPreferred

To specify a read preference, you can use either:要指定读取首选项，可以使用以下任一项：

• The readPreference connection string option when connecting to the node.连接到节点时的readPreference连接字符串选项。
• The Mongo.setReadPref() method.Mongo.setReadPref()方法。

When using mongosh to connect directly to a secondary replica set member, if your read preference is set to primaryPreferred, secondary or secondaryPreferred it is not required to run rs.secondaryOk().使用mongosh直接连接到secondary副本集成员时，如果您的读取首选项设置为primaryPreferred、secondary或secondaryPreferred，则不需要运行rs.secondaryOk()。

show Helper Methods帮助方法

The following show helper methods always use a read preference of primaryPreferred, even when a different read preference has been specified for the operation:以下show helper方法始终使用primaryPreferred的读取首选项，即使为操作指定了不同的读取首项：

• show dbs
• show databases
• show collections
• show tables

In the legacy mongo shell, these operations use the specified read preference.在遗留的mongoshell中，这些操作使用指定的读取首选项。

Constructors构造函数

The following constructors do not work:以下构造函数不起作用：

// This code will fail
class FindResults {
   constructor() {
      this.value = db.students.find();
   }
}

// This code will fail
function listEntries() { return db.students.find(); }
class FindResults {
   constructor() {
      this.value = listEntries();
   }
}

Use an async function instead:请改用async函数：

class FindResults {
   constructor() {
      this.value = ( async() => {
         return db.students.find();
      } )();
   }
}

class FindResults {
   constructor() { }

   init() { this.value = db.students.find(); }
 }

Generator Functions发电机功能

The following generator functions do not work:以下生成器功能不起作用：

// This code will fail
function* FindResults() {
   yield db.students.findMany();
}

// This code will fail
function listEntries() { return db.students.findMany(); }
function* findResults() {
   yield listEntries();
}

Use an async generator function instead:请改用async generator function：

function listEntries() { return db.students.findMany(); }
async function* findResults() {
   yield listEntries();
}

Array Sort数组排序

The following array sort does not work:以下数组排序不起作用：

// This code will fail
db.getCollectionNames().sort( ( collectionOne, collectionTwo ) => {
  return db[ collectionOne ].estimatedDocumentCount() - db[ collectionOne ].estimatedDocumentCount() )
} );

Use .map() instead.请改用.map()。

db.getCollectionNames().map( collectionName => {
   return { collectionName, size: db[ collectionName ].estimatedDocumentCount() };
} ).sort( ( collectionOne, collectionTwo ) => {
   return collectionOne.size - collectionTwo.size;
} ).map( collection => collection.collectionName);

This approach to array sort is often more performant than the equivalent unsupported code.这种数组排序方法通常比等效的不受支持的代码更具性能。