变更流允许应用程序访问实时数据更改,从而避免事先手动追踪 oplog 的复杂性和风险。应用程序可使用变更流来订阅针对单个集合、数据库或整个部署的所有数据变更,并立即对它们做出响应。由于变更流采用聚合框架,因此,应用程序还可对特定变更进行过滤,或是随意转换通知。 从MongoDB 5.1 开始,我们对变更流进行了优化,提高了...
cname db.getCollectionInfos([filter]) - returns a list that contains the names and options of the db's collections db.getCollectionNames() db.getLastError() - just returns the err msg string db.getLastErrorObj() - return full status object db.getLogComponents() db.getMongo() get the ...
MongoDB使用 dot 访问数组的元素,或内嵌doc字段。 MongoDB uses the dot notation to access the elements of an array and to access the fields of an embedded document. users={ name:"t1", age:21, address: {phone:123,email:"xxx@163.com"}, followers:[{name:"a"},{name:"b"},{name:"c"...
To query if the array field contains at leastelement with the specified value, construct a filter using themethod, whereis the element value to match: The following example queries for all documents wheretagsis an array that contains the string"red"as one of its elements: ...
(10) } ] }) However, if you pay close attention to the order above, you may notice that it contains a few errors: The totalWithVAT attribute value is incorrect (it should be equal to 141*1.20=169.2) The total attribute value is incorrect (it should be equal to the sum of each ...
keySet.contains(fieldName)) doc.get(fieldName).asInstanceOf[Option[MGOBlob]] else None } def mgoGetArrayOrNone(doc: Document, fieldName: String) = { if (doc.keySet.contains(fieldName)) doc.get(fieldName).asInstanceOf[Option[MGOArray]] else None } def mgoArrayToDocumentList(arr: MGO...
"errmsg" : "exception: $unwind: value at end of field path must be an array", "code" : 15978, "ok" : 0 } at src/mongo/shell/collection.js:L898 d.如果$unwind目标字段数组为空的话,该文档也将会被忽略。 6.$group 对数据进行分组 ...
[filter]) - returns a list that contains the names and options of the db's collections db.getCollectionNames() db.getLastError() - just returns the err msg string db.getLastErrorObj() - return full status object db.getLogComponents() db.getMongo() get the server connection object db.get...
hello返回文档描述mongod实例角色的文档。 如果指定了可选字段saslSupportedMechs,该命令还会返回array of SASL mechanisms,用于创建指定用户的凭证。 如果该实例是副本集的节点,则hello会返回副本集配置和状态的子集,包括该实例是否是副本集的主节点。 当发送到不是副本集节点的mongod实例时,hello会返回此信息的子集。
The GitHub release contains a detached signature file for the NPM package (namedmongodb-X.Y.Z.tgz.sig). The following command returns the link npm package. npm view mongodb@vX.Y.Z dist.tarball Using the result of the above command, acurlcommand can return the official npm package for th...