在MongoDB中仅减少一个值？
首先让我们创建一个包含文档的集合-
>db.decrementingOperationDemo.insertOne({"ProductName":"Product-1","ProductPrice":756});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd7a8ae6d78f205348bc63c")
}
>db.decrementingOperationDemo.insertOne({"ProductName":"Product-2","ProductPrice":890});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd7a8b86d78f205348bc63d")
}
>db.decrementingOperationDemo.insertOne({"ProductName":"Product-3","ProductPrice":994});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd7a8c66d78f205348bc63e")
}
>db.decrementingOperationDemo.insertOne({"ProductName":"Product-4","ProductPrice":1000});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd7a8d06d78f205348bc63f")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.decrementingOperationDemo.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5cd7a8ae6d78f205348bc63c"),
"ProductName" : "Product-1",
"ProductPrice" : 756
}
{
"_id" : ObjectId("5cd7a8b86d78f205348bc63d"),
"ProductName" : "Product-2",
"ProductPrice" : 890
}
{
"_id" : ObjectId("5cd7a8c66d78f205348bc63e"),
"ProductName" : "Product-3",
"ProductPrice" : 994
}
{
"_id" : ObjectId("5cd7a8d06d78f205348bc63f"),
"ProductName" : "Product-4",
"ProductPrice" : 1000
}以下是查询递减单个值-
> db.decrementingOperationDemo.update({_id: ObjectId("5cd7a8d06d78f205348bc63f"), ProductPrice: {$gt: 0}}, {$inc: {ProductPrice: -10}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })让我们再次检查文档-
> db.decrementingOperationDemo.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5cd7a8ae6d78f205348bc63c"),
"ProductName" : "Product-1",
"ProductPrice" : 756
}
{
"_id" : ObjectId("5cd7a8b86d78f205348bc63d"),
"ProductName" : "Product-2",
"ProductPrice" : 890
}
{
"_id" : ObjectId("5cd7a8c66d78f205348bc63e"),
"ProductName" : "Product-3",
"ProductPrice" : 994
}
{
"_id" : ObjectId("5cd7a8d06d78f205348bc63f"),
"ProductName" : "Product-4",
"ProductPrice" : 990
}