如何在MongoDB中将字符串添加到整个列？
使用聚合框架将字符串添加到MongoDB中的整个列。首先让我们创建一个包含文档的集合-
> db.prependDemo.insertOne({"StudentFirstName":"John"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ccf3bcedceb9a92e6aa1955")
}
> db.prependDemo.insertOne({"StudentFirstName":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ccf3bd3dceb9a92e6aa1956")
}
> db.prependDemo.insertOne({"StudentFirstName":"Robert"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ccf3bd8dceb9a92e6aa1957")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.prependDemo.find().pretty();
这将产生以下输出-
{ "_id" : ObjectId("5ccf3bcedceb9a92e6aa1955"), "StudentFirstName" : "John" }
{
"_id" : ObjectId("5ccf3bd3dceb9a92e6aa1956"),
"StudentFirstName" : "Chris"
}
{
"_id" : ObjectId("5ccf3bd8dceb9a92e6aa1957"),
"StudentFirstName" : "Robert"
}这是将字符串添加到MongoDB中整个列的查询-
> db.prependDemo.aggregate([{
... $project: {
... "StudentFirstName": {
... $concat: ["Mr.", "$StudentFirstName"]
... }
... }
... }]);这将产生以下输出-
{ "_id" : ObjectId("5ccf3bcedceb9a92e6aa1955"), "StudentFirstName" : "Mr.John" }
{ "_id" : ObjectId("5ccf3bd3dceb9a92e6aa1956"), "StudentFirstName" : "Mr.Chris" }
{ "_id" : ObjectId("5ccf3bd8dceb9a92e6aa1957"), "StudentFirstName" : "Mr.Robert" }