MongoDB entry-add, delete, modify, and query-mongodb entry-add, delete

MongoDB entry-add, delete, modify, and query-mongodb entry-add, delete

Mongodb has been successfully started in the previous blog: continue. Open another cmd and enter the [mongo] command to open the shell, that is, the mongodb client. The "test" database is connected by default. Here I set the Set (table) as student. Figure 1:

1. Add insert

Syntax: db. Set. insert ({"Col1": "column value 1", "Col2": "column value 2 ",...," Coln ":" column value n "})

2. find
2.1 All queries

Syntax: db. Set. find ()

2.2 conditional Query

Syntax: db. Set. find ({"Col1": "column value 1", "Col2": "column value 2 ",...," Coln ":" column value n "})

Operation example: Add + search

 
Note: The "_ id" field is the GUID that the database uses by default to ensure data uniqueness.

3. Modify
3.1 modify update all

Syntax: db. Set. update ({"Col": "column value" },{ "Col2": "column value 2 ",...," Coln ":" column value n "})

Note:

First parameter {...} Is the "Search Condition", the second parameter {...} Is the value to be updated ";
Update () is changed to all. The second parameter must contain all "fields". Otherwise, data will be lost after the Update. For details about the impact, see the example.

Operation example: modify all + error instances

3. 2. Local Modification

Mongodb provides two modifiers for local modifications: $ inc and $ set.

① $ Inc Modifier
$ Inc is short for increase. It is a value specified by auto-increment $ inc. If this key is not found in the document, a key is created.

Syntax: db. set. update ({"col1": "column value 1"}, {$ inc: {"col2": "column value 2 ",..., "coln": "column value n "}}

② $ Set Modifier

Replace the corresponding data with the value specified by $ set.

Syntax: db. set. update ({"col1": "column value 1"}, {$ set: {"col2": "column value 2 ",..., "coln": "column value n "}})

Operation example: local modification + advanced Modification

3.3 upsert operation

Upsert = update + insert: intelligently identifies updates or additions, so I prefer to call it advanced modifications. That is to say, if the document is found to be updated directly, otherwise a new one will be added to the database. Set the third parameter of update to true. For operation examples, see.

Syntax: db. Set. update ({"Col": "column value" },{ $ inc: {"Col2": "column value 2 ",..., "Coln": "column value n" }}, true)

3.4 batch Modification

Improvements should be made on the basis of the previous several, rather than explanations.
Syntax: db. Set. update ({"Col": "column value" },{ $ inc: {"Col2": "column value 2 ",..., "Coln": "column value n" }}, true, true)

Operation example: Batch Modification

4. Delete remove

Syntax: db. Set. remove ()
Db. Set. remove ({"Col": "column value" },{ "Col2": "column value 2 ",..., "Coln": "column value n "})

Operation example: Delete

(5 ~ 6. Advanced operations are not described in detail)

5. query groups by group

Operation example: Group Search

6. distinct Removal
7. count statistics

Operation example: deduplication + statistics

The above is the instance sharing after my operation. After I perform the operation again, I feel more gains. I still remember that when I first started the operation, I only touched on all the modifications. At that time, I thought that the modification was an update () method just like other database operations, therefore, some modifications were made directly in practice, resulting in data loss as shown in the figure. At that time, I was still thinking, "No, do you have to write all the changes to only one or two fields? This is too much trouble ...", Later, I discussed with Dr. Zhou Xiang next to him that he told me that there are two ways to modify mongodb: The specific modification methods encapsulated by mongodb mentioned above. At that time, it seemed to have taken a detour. But now, do you think it is actually a detour?