MongoDB-如何将行复制到新创建的集合中？
要将行复制到另一个集合中，请使用MongoDB。语法如下，其中“yourOldCollectionName”是旧集合，而此集合将被复制的地方是我们的新集合，即“yourNewCollectionName”-
db.yourOldCollectionName.aggregate([{ $sample: { size: 333333 }}, {$out: "yourNewCollectionName"} ],{allowDiskUse: true});首先让我们创建一个包含文档的集合-
> db.sourceCollection.insertOne({"EmployeeName":"Robert","EmployeeSalary":15000});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e0397c1f5e889d7a5199506")
}
> db.sourceCollection.insertOne({"EmployeeName":"David","EmployeeSalary":25000});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e0397c3f5e889d7a5199507")
}
> db.sourceCollection.insertOne({"EmployeeName":"Mike","EmployeeSalary":29000});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e0397c4f5e889d7a5199508")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.sourceCollection.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5e0397c1f5e889d7a5199506"),
"EmployeeName" : "Robert",
"EmployeeSalary" : 15000
}
{
"_id" : ObjectId("5e0397c3f5e889d7a5199507"),
"EmployeeName" : "David",
"EmployeeSalary" : 25000
}
{
EmployeeName" : "Mike",
"E"_id" : ObjectId("5e0397c4f5e889d7a5199508"),
"mployeeSalary" : 29000
}这是创建新集合“destinationCollection”的查询-
> db.createCollection('destinationCollection');
{ "ok" : 1 }以下是将行从“sourceCollection”复制到另一个新集合“destinationCollection”的查询-
> db.sourceCollection.aggregate([{ $sample: { size: 333333 }}, {$out: "destinationCollection"} ],{allowDiskUse: true});以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.destinationCollection.find().pretty()
这将产生以下输出，其中新集合从第一个集合“sourceCollection”复制记录-
{
"_id" : ObjectId("5e0397c4f5e889d7a5199508"),
"EmployeeName" : "Mike",
"EmployeeSalary" : 29000
}
{
"_id" : ObjectId("5e0397c3f5e889d7a5199507"),
"EmployeeName" : "David",
"EmployeeSalary" : 25000
}
{
"_id" : ObjectId("5e0397c1f5e889d7a5199506"),
"EmployeeName" : "Robert",
"EmployeeSalary" : 15000
}