在MongoDB中执行条件更新或更新
对于有条件的更新或更新，可以使用$max运算符。首先让我们创建一个包含文档的集合
>db.conditionalUpdatesDemo.insertOne({"_id":100,"StudentFirstScore":89,"StudentSecondScore":78,"BiggestScore":89});
{ "acknowledged" : true, "insertedId" : 100 }
>db.conditionalUpdatesDemo.insertOne({"_id":101,"StudentFirstScore":305,"StudentSecondScore":560,"BiggestScore":1050});
{ "acknowledged" : true, "insertedId" : 101 }
>db.conditionalUpdatesDemo.insertOne({"_id":103,"StudentFirstScore":560,"StudentSecondScore":789,"BiggestScore":880});
{ "acknowledged" : true, "insertedId" : 103 }
Following is the query to display all documents from a collection with the help of find() method:
> db.conditionalUpdatesDemo.find().pretty();这将产生以下输出
{
"_id" : 100,
"StudentFirstScore" : 89,
"StudentSecondScore" : 78,
"BiggestScore" : 89
}
{
"_id" : 101,
"StudentFirstScore" : 305,
"StudentSecondScore" : 560,
"BiggestScore" : 1050
}
{
"_id" : 103,
"StudentFirstScore" : 560,
"StudentSecondScore" : 789,
"BiggestScore" : 880
}以下是对MongoDB中的条件更新或更新的查询
> db.conditionalUpdatesDemo.update( { _id: 100 }, { $max: { "BiggestScore": 150 } } );
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })让我们检查“_id100”字段“BiggestScore”的值是否已更新为150
> db.conditionalUpdatesDemo.find().pretty();
这将产生以下输出
{
"_id" : 100,
"StudentFirstScore" : 89,
"StudentSecondScore" : 78,
"BiggestScore" : 150
}
{
"_id" : 101,
"StudentFirstScore" : 305,
"StudentSecondScore" : 560,
"BiggestScore" : 1050
}
{
"_id" : 103,
"StudentFirstScore" : 560,
"StudentSecondScore" : 789,
"BiggestScore" : 880
}