获取 MongoDB 中更新的文档数量?
mongodbdatabasebig data analytics更新于 2026/1/25 15:52:17
要获取 MongoDB 中更新的文档数量，您需要结合使用 runCommand 和 getlasterror。
首先，我们创建一个包含文档的集合
> db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"David"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ca28c1d6304881c5ce84bad")
}
> db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ca28c226304881c5ce84bae")
}
> db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"Robert"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ca28c276304881c5ce84baf")
}
> db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"Ramit"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ca28c366304881c5ce84bb0")
}
> db.getNumberOfUpdatedDocumentsDemo.insertOne({"StudentName":"Adam"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ca28c436304881c5ce84bb1")
}
以下是借助 find() 方法显示集合中的所有文档的查询:
> db.getNumberOfUpdatedDocumentsDemo.find().pretty();
这将产生以下输出 −
{ "_id" : ObjectId("5ca28c1d6304881c5ce84bad"), "StudentName" : "David" }
{ "_id" : ObjectId("5ca28c226304881c5ce84bae"), "StudentName" : "Chris" }
{ "_id" : ObjectId("5ca28c276304881c5ce84baf"), "StudentName" : "Robert" }
{ "_id" : ObjectId("5ca28c366304881c5ce84bb0"), "StudentName" : "Ramit" }
{ "_id" : ObjectId("5ca28c436304881c5ce84bb1"), "StudentName" : "Adam" }
以下是更新文档的查询
> db.getNumberOfUpdatedDocumentsDemo.update({}, {$set : {"StudentName" : "Carol"}}, true, true);
WriteResult({ "nMatched" : 5, "nUpserted" : 0, "nModified" : 5 })
Now, get the number of updated documents:
> db.runCommand( "getlasterror" );
以下输出显示 n = 5，即已更新 5 个文档
{
"connectionId" : 4,
&"updatedExisting" : true,
&"n" : 5,
&"syncMillis" : 0,
&"writtenTo" : null,
&"err" : null,
&"ok" : 1
}
现在显示集合中的所有文档
> db.getNumberOfUpdatedDocumentsDemo.find().pretty();
这将产生以下输出 −
{ "_id" : ObjectId("5ca28c1d6304881c5ce84bad"), "StudentName" : "Carol" }
{ "_id" : ObjectId("5ca28c226304881c5ce84bae"), "StudentName" : "Carol" }
{ "_id" : ObjectId("5ca28c276304881c5ce84baf"), "StudentName" : "Carol" }
{ "_id" : ObjectId("5ca28c366304881c5ce84bb0"), "StudentName" : "Carol" }
{ "_id" : ObjectId("5ca28c436304881c5ce84bb1"), "StudentName" : "Carol" }
