Configure CRUD Operations配置CRUD操作

Client Configuration客户端配置

This example shows how to set the read preference, read concern, and write concern of a MongoClient instance by passing a MongoClientOptions object to the constructor. The code configures the following settings:此示例显示了如何通过将MongoClientOptions对象传递给构造函数来设置MongoClient实例的读取首选项、读取关注和写入关注。该代码配置了以下设置：

• SECONDARY read preference: Read operations retrieve data from secondary replica set members读取首选项：读取操作从辅助副本集成员检索数据
• local read concern: Read operations return the instance's most recent data without guaranteeing that the data has been written to a majority of the replica set members读取关注：读取操作返回实例的最新数据，但不保证数据已写入大多数副本集成员
• 2 write concern: The primary and one secondary replica set member must acknowledge the write operation写入关注：主副本集成员和一个辅助副本集成员必须确认写入操作

const clientOptions = {
  readPreference: ReadPreference.SECONDARY,
  readConcern: { level: "local" },
  writeConcern: { w: 2 },
};

const client = new MongoClient("mongodb://localhost:27017", clientOptions);

Alternatively, you can specify the read and write settings in the connection URI, which is passed as a parameter to the MongoClient constructor:或者，您可以在连接URI中指定读写设置，该URI作为参数传递给MongoClient构造函数：

const uri = "mongodb://localhost:27017/?readPreference=secondary&readConcernLevel=local&w=2";
const clientWithUri = new MongoClient(uri);

Transaction Configuration事务配置

This example shows how to set the read preference, read concern, and write concern of a transaction by passing a TransactionOptions object to the startTransaction() method. The code configures the following settings:此示例显示了如何通过将TransactionOptions对象传递给startTransaction()方法来设置事务的读取首选项、读取关注和写入关注。该代码配置了以下设置：

• PRIMARY read preference: Read operations retrieve data from the primary replica set member读取首选项：读取操作从主副本集成员检索数据
• majority read concern: Read operations return the instance's most recent data that has been written to a majority of replica set members读取关注：读取操作返回已写入大多数副本集成员的实例的最新数据
• 1 write concern: The primary replica set member must acknowledge the write operation写入关注：主副本集成员必须确认写入操作

const transactionOptions = {
  readPreference: ReadPreference.PRIMARY,
  readConcern: { level: "majority" },
  writeConcern: { w: 1 },
};

const session = client.startSession();
session.startTransaction(transactionOptions);

Database Configuration数据库配置

This example shows how to set the read preference, read concern, and write concern of a database called test_database by passing a DbOptions object to the db() method. The code configures the following settings:此示例显示了如何通过将DbOptions对象传递给db()方法来设置名为test_database的数据库的读取首选项、读取关注和写入关注。该代码配置了以下设置：

• PRIMARY_PREFERRED read preference: Read operations retrieve data from the primary replica set member, or secondary members if the primary is unavailable读取首选项：读取操作从主副本集成员或辅助成员（如果主副本不可用）检索数据
• available read concern: Read operations return the instance's most recent data without guaranteeing that the data has been written to a majority of the replica set members读取关注：读取操作返回实例的最新数据，但不保证数据已写入大多数副本集成员
• majority write concern: The majority of all replica set members must acknowledge the write operation写入关注：大多数副本集成员必须确认写入操作

const dbOptions = {
  readPreference: ReadPreference.PRIMARY_PREFERRED,
  readConcern: { level: "available" },
  writeConcern: { w: "majority" },
};

const db = client.db("test_database", dbOptions);

Collection Configuration集合配置

This example shows how to set the read preference, read concern, and write concern of a collection called test_collection by passing a CollectionOptions object to the collection() method. The code configures the following settings:此示例显示了如何通过将CollectionOptions对象传递给collection()方法来设置名为test_collection的集合的读取首选项、读取关注和写入关注。该代码配置了以下设置：

• SECONDARY_PREFERRED read preference: Read operations retrieve data from secondary replica set members, or the primary members if no secondaries are available读取首选项：读取操作从辅助副本集成员检索数据，如果没有辅助副本集可用，则从主成员检索数据
• available read concern: Read operations return the instance's most recent data without guaranteeing that the data has been written to a majority of the replica set members读取关注：读取操作返回实例的最新数据，但不保证数据已写入大多数副本集成员
• 0 write concern: Does not request acknowledgment of the write operation写入关注：不请求确认写入操作

const collOptions = {
  readPreference: ReadPreference.SECONDARY_PREFERRED,
  readConcern: { level: "available" },
  writeConcern: { w: 0 },
};

const collection = db.collection("test_collection", collOptions);

Collation Fields排序字段

The collation object contains the following fields:排序规则对象包含以下字段：

collation: {
  locale: <string>,
  caseLevel: <bool>,
  caseFirst: <string>,
  strength: <int>,
  numericOrdering: <bool>,
  alternate: <string>,
  maxVariable: <string>,
  backwards: <bool>
}

When setting the collation option, you must specify the locale field. All other fields are optional. 设置collation选项时，必须指定locale字段。所有其他字段都是可选的。For a complete list of supported locales and the default values for the locale fields, see Supported Languages and Locales in the MongoDB Server manual.有关支持的区域设置和locale字段默认值的完整列表，请参阅MongoDB服务器手册中的支持的语言和区域设置。

Collation Examples排序示例

To specify a collation, create a collation object and set its locale field to the language collation you want to use. Then, pass this object as an options parameter to the method corresponding to the target collation level.若要指定排序规则，请创建collation对象，并将其locale字段设置为要使用的语言排序规则。然后，将此对象作为选项参数传递给与目标排序规则级别对应的方法。

This section includes examples that set collations at the collection, index, and operation levels.本节包括在集合、索引和操作级别设置排序规则的示例。

const db = client.db("db")
db.createCollection("names", {
  collation: { locale: "fr_CA" },
});

const coll = db.collection("names");
coll.createIndex(
  { "last_name" : 1 },
  { "collation" : { "locale" : "en_US" } });

{ "_id" : 1, "first_name" : "Hans", "last_name" : "Muller" }
{ "_id" : 2, "first_name" : "Gunter", "last_name" : "Braun" }
{ "_id" : 3, "first_name" : "Günter", "last_name" : "Krause" }
{ "_id" : 4, "first_name" : "Jürgen", "last_name" : "Weber" }

coll.findOneAndUpdate(
  { first_name: { $lt: "Gunter" } },
  { $set: { verified: true } },
  { collation: { locale: "de@collation=phonebook" } },
);

{ lastErrorObject: { updatedExisting: true, n: 1 },
  value: { _id: 3, first_name: 'Günter', last_name: 'Krause' },
  ok: 1 }