[MongoDB Learning Notes 9] in-depth MongoDB update (update) operation: modifier $inc

After the ongoDB document is stored in the database, the update method is used to update the document. The update method has two parameters, such as

Update (args1,args2)

Args1 refers to the conditions for querying documents.

Args2 refers to what kind of changes are made to the documents queried.

$inc is used to increase the used key value, and if the key does not exist, create it

The key values that can only be modified by $Inc must be integers, long integers, and double-precision floating-point values, not other types.

Use $inc to increase the key value:

> db.post.findOne ({"id": 0}) {"_ id": ObjectId ("54a530c3ff0df3732bac167f"), "id": 0, "name": "joe", "age": 65, "comments": {"1": 4, "2": 2 "3": 3}} > db.post.update ({"id": 0}, {$inc: {"age": 6}}) WriteResult ({"nMatched": 1, "nUpserted": 0, "nModified": 1})

The modified result:

> db.post.findOne ({"id": 0}) {"_ id": ObjectId ("54a530c3ff0df3732bac167f"), "id": 0, "name": "joe", "age": 71, "comments": {"1": 4, "2": 2 "3": 3}}

Use $inc to reduce the key value:

> db.post.update ({"id": 0}, {$inc: {"age":-16}}) WriteResult ({"nMatched": 1, "nUpserted": 0, "nModified": 1})

The modified result:

> db.post.findOne ({"id": 0}) {"_ id": ObjectId ("54a530c3ff0df3732bac167f"), "id": 0, "name": "joe", "age": 55, "comments": {"1": 4, "2": 2 "3": 3}} >