MongoDB事务和索引以获取重复值
在数组内部使用ensureIndex()并设置unique：1。让我们创建一个包含文档的集合-
> db.demo298.save({Name: 'Chris', Marks: [46, 79] });
WriteResult({ "nInserted" : 1 })
> db.demo298.save({Name: 'David', Marks: [67, 88] });
WriteResult({ "nInserted" : 1 })
> db.demo298.ensureIndex({ Marks: 1 }, {unique: 1});
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
> db.demo298.save({Name: 'Mike', Marks: [88,98] });
WriteResult({
"nInserted" : 0,
"writeError" : {
"code" : 11000,
"errmsg" : "E11000 duplicate key error collection: test.demo298 index: Marks_1 dup key: { : 88.0 }"
}
})在find()方法的帮助下显示集合中的所有文档-
> db.demo298.find();
这将产生以下输出-
{ "_id" : ObjectId("5e4d56e55d93261e4bc9ea48"), "Name" : "Chris", "Marks" : [ 46, 79 ] }
{ "_id" : ObjectId("5e4d56f55d93261e4bc9ea49"), "Name" : "David", "Marks" : [ 67, 88 ] }