```
> db.user.find()
{ "_id" : ObjectId("56d7ced2a2aed7154cef7b03"), "email" : "[email protected]", "first_name" : "Ross", "last_name" : "Lawley" }
{ "_id" : ObjectId("56d7d730a2aed7160b3f06c8"), "email" : "content", "first_name" : "xu", "last_name" : "yundong" }
> db.user.find({'email': {$regex: '^(.*@.*)$'}})
{ "_id" : ObjectId("56d7ced2a2aed7154cef7b03"), "email" : "[email protected]", "first_name" : "Ross", "last_name" : "Lawley" }
```

这个是使用正则，匹配 @符号