sparse and unique Properties An index that is both sparse and unique prevents collection from having documents with duplicate values for a field but allows multiple documents that omit the key.例子 在A集合上创建稀疏索引 Consider a collection scores that contains the following documents: { "_id" ...
db.values.ensureIndex({open: 1, close: 1}) 1. 这个命令会触发索引创建的两个过程,一个是将相应的字段排序,因为索引是按B+树来组织的,要构建树,将数据进行排序后能够提高插入B+树的效率(第二个过程的效率),在日志中,你能看到和下面类似的输出: Tue Jan 4 09:58:17 [conn1] building new index on ...
说明: 若插入的数据主键已经存在,则会抛 org.springframework.dao.DuplicateKeyException 异常,提示主键重复,不保存当前数据。 案例: 如向集合user_demo中插入一条数据: db.user_demo.insert({"name":"zhangsan","age":18})# 相当于sql中的insert into user_demo(name, age) values("zhangsan",18); 1.2 使...
db.students.find({"age":19}).explain();{"queryPlanner":{"plannerVersion":1,"namespace":"mldn.students","indexFilterSet":false,"parsedQuery":{"age":{"$eq":19}},"winningPlan":{"stage":"FETCH","inputStage":{"stage":"IXSCAN","keyPattern":{"age":-1},"indexName":"age_-1","i...
insert()方法插入文档时,若集合中存在该文档,则会报E11000 duplicate key error collection错误,反之则写入。 save()方法插入文档时,若集合中存在该文档,则会更新它,反之则写入。 insertMany()是用于插入多个文档的方法,该方法的参数是一个由多个文档组成的数组。
For example, inserting a BSON document with duplicate field names through a MongoDB driver may result in the driver silently dropping the duplicate values prior to insertion, or may result in an invalid document being inserted that contains duplicate fields. Querying those documents leads to inconsis...
All values of a field All fields in a document All fields in a document except specific field paths Multiple specific fields in a document To learn more, seeWildcard Indexes. Index Properties Unique Indexes Theuniqueproperty for an index causes MongoDB to reject duplicate values for the indexed...
这个问题是我带的徒弟今天遇到的,程序在向mongodb中插入数据时出现id重复的错误,出错的提示如下: duplicate key error collection: index: id dup key...默认情况下id字段的类型为ObjectId,它是MongoDB的BSON类型之一。如果用户需要还可以将id设置为...
insert: 若插入的数据主键已经存在,则会抛 DuplicateKeyException 异常,提示主键重复,不保存当前数据 save: 如果_id主键存在则更新数据,如果不存在就插入数据。 > db.emp.insert({name:"张三",age:12}) WriteResult({ "nInserted" : 1 }) > db.emp.save({name:"李四",age:3}) WriteResult({ "nInserted...
$ne Matches all values that are not equal to a specified value.(不等于) $nin Matches none of the values specified in an array.(不包含) 12.2.1、查询age是22的student信息 > db.student.find({ age:22 }) { "_id" : ObjectId("611b6ab90ad895f9d53f39d9"), "name" : "bill01", "ag...