在 MongoDB 中只减少一个值?
mongodbdatabasebig data analytics更新于 2026/1/14 2:52:17
首先，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")
}
以下是使用 find() 方法显示集合中的所有文档的查询 −
> 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
}
以下查询将单个值减一
> db.decrementingOperationDemo.update({_id: ObjectId("5cd7a8d06d78f205348bc63f"), ProductPrice: {$gt: 0}}, {$inc: {ProductPrice: -10}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
让我们再次检查一下文档 −
> 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
}
