如何在MongoDB中的update()函数内部递增？
您可以使用$inc运算符来递增。首先让我们创建一个包含文档的集合-
> db.addInUpdateFunctionDemo.insertOne({"PlayerName":"Chris","PlayerScore":78});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd2b3f4345990cee87fd893")
}
> db.addInUpdateFunctionDemo.insertOne({"PlayerName":"Robert","PlayerScore":88});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd2b3fc345990cee87fd894")
}
> db.addInUpdateFunctionDemo.insertOne({"PlayerName":"David","PlayerScore":99});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd2b407345990cee87fd895")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.addInUpdateFunctionDemo.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5cd2b3f4345990cee87fd893"),
"PlayerName" : "Chris",
"PlayerScore" : 78
}
{
"_id" : ObjectId("5cd2b3fc345990cee87fd894"),
"PlayerName" : "Robert",
"PlayerScore" : 88
}
{
"_id" : ObjectId("5cd2b407345990cee87fd895"),
"PlayerName" : "David",
"PlayerScore" : 99
}以下是update()在MongDB中的函数内部执行加法的查询-
> db.addInUpdateFunctionDemo.update({_id : ObjectId("5cd2b407345990cee87fd895")},{$inc: {PlayerScore: 201}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })让我们再次检查所有文件-
> db.addInUpdateFunctionDemo.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5cd2b3f4345990cee87fd893"),
"PlayerName" : "Chris",
"PlayerScore" : 78
}
{
"_id" : ObjectId("5cd2b3fc345990cee87fd894"),
"PlayerName" : "Robert",
"PlayerScore" : 88
}
{
"_id" : ObjectId("5cd2b407345990cee87fd895"),
"PlayerName" : "David",
"PlayerScore" : 300
}