3.mongodb query
MongoDB queries documents using the find () method.
The find () method displays all documents in an unstructured way.
The syntax format is as follows:
Db.collection.find (query, projection)
Query: optional, use the query operator to specify query conditions
Projection: optionally, use the projection operator to specify the returned key. When querying, all the key values in the document are returned, simply omitting the parameter (default omitted).
# after adding the pretty method to find, you can also display it in a format that is easier to read:
Db.tmp.find ()
{"_ id": ObjectId ("5c1757c7f4e84940e0bd578b"), "name": "aaa", "pwd": "123"," birthday ": ISODate (" 1995-09-05T00:00:00Z ")}
{"_ id": ObjectId ("5c1757f5f4e84940e0bd578c"), "name": "bbb", "pwd": "321", "birthday": ISODate ("1999-10-10T00:00:00Z")}
{"_ id": ObjectId ("5c177b84f4e84940e0bd578d"), "name": "suhaozhi", "pwd": "suhaozhi", "phone": [{"phone_num": "13333333333", "type": "cmcc"}, {"phone_num": 1555555555, "type": "chinanet"}], "type": "chinanet"}
{"_ id": ObjectId ("5c177ba1f4e84940e0bd578e"), "name": "suhaozhi", "pwd": "su", "phone": [{"phone_num": "13333333332", "type": "cmcc"}, {"phone_num": 15655555555, "type": "cnnet"}]}
{"_ id": ObjectId ("5c178a62b1d327866c98c9f7"), "x": "y"}
{"_ id": ObjectId ("5c1f226c87756129d06d2718"), "username": "aaa", "phone_num": "13333333333"}
{"_ id": ObjectId ("5c1f232587756129d06d2719"), "username": "bbb", "phone_num": ["123,456"]}
Mgset-6039947:PRIMARY > db.tmp.find (). Pretty ()
{
"_ id": ObjectId ("5c1757c7f4e84940e0bd578b")
"name": "aaa"
Pwd: 123,
Birthday: ISODate ("1995-09-05T00:00:00Z")
}
{
"_ id": ObjectId ("5c1757f5f4e84940e0bd578c")
"name": "bbb"
Pwd: 321
Birthday: ISODate ("1999-10-10T00:00:00Z")
}
{
"_ id": ObjectId ("5c177b84f4e84940e0bd578d")
"name": "suhaozhi"
"pwd": "suhaozhi"
"phone": [
{
"phone_num": "13333333333"
"type": "cmcc"
}
{
"phone_num": 155555555555
"type": "chinanet"
}
]
"type": "chinanet"
}
{
"_ id": ObjectId ("5c177ba1f4e84940e0bd578e")
"name": "suhaozhi"
"pwd": "su"
"phone": [
{
"phone_num": "13333333332"
"type": "cmcc"
}
{
"phone_num": 15655555555
"type": "cnnet"
}
]
}
{"_ id": ObjectId ("5c178a62b1d327866c98c9f7"), "x": "y"}
{
"_ id": ObjectId ("5c1f226c87756129d06d2718")
"username": "aaa"
"phone_num": "13333333333"
}
{
"_ id": ObjectId ("5c1f232587756129d06d2719")
"username": "bbb"
"phone_num": [
"123"
"456"
]
}
Query criteria:
If you are familiar with regular SQL data, you can better understand MongoDB conditional queries through the following table:
The similar statement in the operation format example RDBMS is equal to {:} db.col.find ({"by": "Rookie tutorial"}). Pretty () where by = 'Rookie tutorial' is less than {: {$lt:}} db.col.find ({"likes": {$lt:50}) .pretty () where likes
< 50小于或等于{:{$lte:}}db.col.find({"likes":{$lte:50}}).pretty()where likes 50大于或等于{:{$gte:}}db.col.find({"likes":{$gte:50}}).pretty()where likes >= 50 is not equal to {: {$ne:}} db.col.find ({"likes": {$ne:50}}) .pretty () where likes! = 50
AND conditional query:
The find () method of MongoDB can pass in multiple keys (key), each key separated by a comma, which is the AND condition of a regular SQL.
Example:
Db.col.find ({key1:value1, key2:value2}) .pretty ()
Or conditional query:
The MongoDB OR conditional statement uses the keyword $or and the syntax format is as follows:
> db.col.find (
{
$or: [
{key1: value1}, {key2:value2}
]
}
). Pretty ()
And is used in conjunction with or:
The following example demonstrates the combined use of AND and OR, similar to the regular SQL statement: 'where age
