在MongoDB中如何追加到数组？
在MongoDB中追加数组，使用$concatArrays。让我们创建一个包含文档的集合
> db.demo435.insertOne({"FirstName":["Chris"],"LastName":["Brown"]} );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e7719b1bbc41e36cc3cae97")
}
> db.demo435.insertOne({"FirstName":["David"],"LastName":["Miller"]} );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e7719bdbbc41e36cc3cae98")
}
> db.demo435.insertOne({"FirstName":["John"],"LastName":["Doe"]} );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e7719c6bbc41e36cc3cae99")
}> db.demo435.find().pretty();
这将产生以下输出
{
"_id" : ObjectId("5e7719b1bbc41e36cc3cae97"),
"FirstName" : [
"Chris"
],
"LastName" : [
"Brown"
]
}
{
"_id" : ObjectId("5e7719bdbbc41e36cc3cae98"),
"FirstName" : [
"David"
],
"LastName" : [
"Miller"
]
}
{
"_id" : ObjectId("5e7719c6bbc41e36cc3cae99"),
"FirstName" : [
"John"
],
"LastName" : [
"Doe"
]
}下面是要追加到MongoDB中的数组的查询
> db.demo435.aggregate([ { $project: { FullName: { $concatArrays: [ "$FirstName", "$LastName" ] } } } ])这将产生以下输出
{ "_id" : ObjectId("5e7719b1bbc41e36cc3cae97"), "FullName" : [ "Chris", "Brown" ] }
{ "_id" : ObjectId("5e7719bdbbc41e36cc3cae98"), "FullName" : [ "David", "Miller" ] }
{ "_id" : ObjectId("5e7719c6bbc41e36cc3cae99"), "FullName" : [ "John", "Doe" ] }