如何在 MongoDB 中合并文档数组?
mongodbdatabasebig data analytics
要合并文档，请使用 `aggregate()` 函数并配合 `$PUSH` 参数。让我们创建一个包含多个文档的集合。
> db.demo64.insertOne({"Subjects":["MySQL","MongoDB","Java"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e28762bcfb11e5c34d89936")
}
> db.demo64.insertOne({"Subjects":["Oracle","Spring","Python"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e28763fcfb11e5c34d89937")
}
借助 find() 方法显示集合中的所有文档 −
> db.demo64.find();
这将产生以下输出 −
{ "_id" : ObjectId("5e28762bcfb11e5c34d89936"), "Subjects" : [ "MySQL", "MongoDB", "Java" ] }
{ "_id" : ObjectId("5e28763fcfb11e5c34d89937"), "Subjects" : [ "Oracle", "Spring", "Python" ] }
以下是 MongoDB 中合并文档数组的查询语句 −
> db.demo64.aggregate([
... { "$group": {
... "_id": null,
... "Subjects": { "$push": "$Subjects" }
... }},
... { "$project": { "_id": 0 }}
... ]);
这将产生以下输出 −
{ "Subjects" : [ [ "MySQL", "MongoDB", "Java" ], [ "Oracle", "Spring", "Python" ] ] }
