在MongoDB中设置唯一索引
要在MongoDB中设置唯一索引，请使用unique：true。让我们创建一个包含文档的集合-
> db.demo257.ensureIndex({Name:1},{unique:true});
{
"createdCollectionAutomatically" : true,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
> db.demo257.insertOne({Name:"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e47a5e51627c0c63e7dba91")
}
> db.demo257.insertOne({Name:"Bob"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e47a5e81627c0c63e7dba92")
}
> db.demo257.insertOne({Name:"Chris"});
2020-02-15T13:33:54.064+0530 E QUERY [js] WriteError: E11000 duplicate key error collection: test.demo257 index: Name_1 dup key: { : "Chris" } :
WriteError({
"index" : 0,
"code" : 11000,
"errmsg" : "E11000 duplicate key error collection: test.demo257 index: Name_1 dup key: { : \"Chris\" }",
"op" : {
"_id" : ObjectId("5e47a5ea1627c0c63e7dba93"),
"Name" : "Chris"
}
})
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在find()方法的帮助下显示集合中的所有文档-
> db.demo257.find();
这将产生以下输出-
{ "_id" : ObjectId("5e47a5e51627c0c63e7dba91"), "Name" : "Chris" }
{ "_id" : ObjectId("5e47a5e81627c0c63e7dba92"), "Name" : "Bob" }