MongoDB查询按单词排序
要按单词排序，请使用$addField和$cond。让我们创建一个包含文档的集合
> db.demo62.insertOne({"Subject":"MySQL"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e287084cfb11e5c34d8992f")
}
> db.demo62.insertOne({"Subject":"MongoDB"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e287085cfb11e5c34d89930")
}
> db.demo62.insertOne({"Subject":"Java"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e287086cfb11e5c34d89931")
}> db.demo62.find();
{ "_id" : ObjectId("5e287084cfb11e5c34d8992f"), "Subject" : "MySQL" }
{ "_id" : ObjectId("5e287085cfb11e5c34d89930"), "Subject" : "MongoDB" }
{ "_id" : ObjectId("5e287086cfb11e5c34d89931"), "Subject" : "Java" }> db.demo62.aggregate([
... {
... $addFields: {
... sortByWords: {
... $cond: [
... { $eq: ["$Subject", "MongoDB"] },
... 0,
... { $cond: [{ $eq: ["$Subject", "MySQL"] }, 1, 2] }
... ]
... }
... }
... },
...
... {
... $sort: {
... sortByWords: 1
... }
... }
... ]);{ "_id" : ObjectId("5e287085cfb11e5c34d89930"), "Subject" : "MongoDB", "sortByWords" : 0 }
{ "_id" : ObjectId("5e287084cfb11e5c34d8992f"), "Subject" : "MySQL", "sortByWords" : 1 }
{ "_id" : ObjectId("5e287086cfb11e5c34d89931"), "Subject" : "Java", "sortByWords" : 2 }