Data query of MongoDB (nested set)
Each collection data in the MongoDB database can continue to save other collection data, for example, some people save family information.
Example: add data
Db.emp.insert ({"name": "Lin A", "sex": "male", "age": 22, "sal": 8000, "loc": "Beijing", "course": ["Chinese", "mathematics", "English", "music", "politics"], "parents": [{"name": "Lin A father", "age": 50, "job": "farmer"}, {"name": "Lin A mother", "age": 49 "job": "worker"}]})
Db.emp.insert ({"name": "Lin B", "sex": "male", "age": 30, "sal": 8000, "loc": "Beijing", "course": ["Chinese", "mathematics"], "parents": [{"name": "Lin B father", "age": 55, "job": "worker"}, {"name": "Lin B mother", "age": 52, "job": "farmer"}]})
Db.emp.insert ({"name": "Lin C", "sex": "male", "age": 35, "sal": 8000, "loc": "Beijing", "course": ["Chinese", "Mathematics", "English"], "parents": [{"name": "Lin C father", "age": 60, "job": "worker"}, {"name": "Lin C mother", "age": 59, "job": "staff"}]})
Db.emp.insert ({"name": "Lin D", "sex": "male", "age": 28, "sal": 8000, "loc": "Beijing", "course": ["Chinese", "Mathematics", "Politics"], "parents": [{"name": "Lin D Father", "age": 58, "job": "Director"}, {"name": "Lin D Mother", "age": 54, "job": "Director"]})
Db.emp.insert ({"name": "Lin E", "sex": "male", "age": 40, "sal": 8000, "loc": "Beijing", "course": ["language", "politics"], "parents": [{"name": "Lin E father", "age": 70, "job": "worker"}, {"name": "Lin E mother", "age": 68, "job": "Secretary"}]})
The content at this time is a nested collection, and the judgment of the data of this collection can only be done through "$elemMatch".
Example: find out the information of the director among the parents.
> db.emp.find ({"$and": [{"age": {"$gte": 30}}, {"parents": {"$elemMatch": {"job": "Director"}}]}) .pretty ()
{
"_ id": ObjectId ("599148bf0184ff511bf02b95")
"name": "Lin E"
"sex": "male"
"age": 40
"sal": 8000
"loc": "Beijing"
"course": [
"Chinese"
"politics"
]
"parents": [
{
"name": "Father Lin E"
"age": 70
"job": "worker
}
{
"name": "Mother Lin E"
"age": 68
"job": "Director"
}
]
}
Since the conditions of this kind of query are troublesome, try not to be so complicated if possible.
