获取MongoDB中的更新文档数量？
要在MongoDB中获取更新文档的数量，您需要将runCommand和getlasterror一起使用。
首先让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")
}以下是在find()方法的帮助下显示集合中所有文档的查询：
> 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" );以下是显示n=5的输出，即5个文档已更新
{
"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" }