避免在MongoDB中重复输入？
为了避免在MongoDB中重复输入，可以使用createIndex()。语法如下-
db.yourCollectionName.createIndex({"yourFieldName":1},{unique:true});让我们实现以上语法。避免在MongoDB中重复条目的查询如下-
> db.avoidDuplicateEntriesDemo.createIndex({"UserName":1},{unique:true});
{
"createdCollectionAutomatically" : true,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}现在在上面的集合中插入一些记录。插入记录的查询如下-
> db.avoidDuplicateEntriesDemo.insertOne({"UserName":"John"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90e1824afe5c1d2279d697")
}每当您尝试再次插入相同记录时，都会出现此错误-
> db.avoidDuplicateEntriesDemo.insertOne({"UserName":"John"});
2019-03-19T18:03:08.465+0530 E QUERY [js] WriteError: E11000 duplicate key error collection: test.avoidDuplicateEntriesDemo index: UserName_1 dup key: { : "John" } :
WriteError({
"index" : 0,
"code" : 11000,
"errmsg" : "E11000 duplicate key error collection: test.avoidDuplicateEntriesDemo index: UserName_1 dup key: { : \"John\" }",
"op" : {
"_id" : ObjectId("5c90e1844afe5c1d2279d698"),
"UserName" : "John"
}
})
WriteError@src/mongo/shell/bulk_api.js:461:48
Bulk/mergeBatchResults@src/mongo/shell/bulk_api.js:841:49
Bulk/executeBatch@src/mongo/shell/bulk_api.js:906:13
Bulk/this.execute@src/mongo/shell/bulk_api.js:1150:21
DBCollection.prototype.insertOne@src/mongo/shell/crud_api.js:252:9
@(shell):1:1让我们插入另一条记录。查询如下-
> db.avoidDuplicateEntriesDemo.insertOne({"UserName":"Carol"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90e18d4afe5c1d2279d699")
}在find()method的帮助下显示集合中的所有文档。查询如下-
> db.avoidDuplicateEntriesDemo.find();
以下是输出-
{ "_id" : ObjectId("5c90e1824afe5c1d2279d697"), "UserName" : "John" }
{ "_id" : ObjectId("5c90e18d4afe5c1d2279d699"), "UserName" : "Carol" }