如何在MongoDB中创建唯一字段？
要在MongoDB中创建唯一字段，请使用unique-true。让我们创建一个包含文档的集合-
> db.demo82.createIndex({"EmployeeName":1},{unique:true});
{
"createdCollectionAutomatically" : true,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
> db.demo82.insertOne({"EmployeeName":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bfb1b71bf0181ecc422a0")
}
> db.demo82.insertOne({"EmployeeName":"David"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bfb1f71bf0181ecc422a1")
}
> db.demo82.insertOne({"EmployeeName":"Chris"});
2020-01-25T13:54:00.410+0530 E QUERY [js] WriteError: E11000 duplicate key error collection: test.demo82 index: EmployeeName_1 dup key: { : "Chris" } :
WriteError({
"index" : 0,
"code" : 11000,
"errmsg" : "E11000 duplicate key error collection: test.demo82 index: EmployeeName_1 dup key: { : \"Chris\" }",
"op" : {
"_id" : ObjectId("5e2bfb2071bf0181ecc422a2"),
"EmployeeName" : "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.demo82.find();
这将产生以下输出。由于我们在上面使用了unique-true，因此重复的值将不会被插入-
{ "_id" : ObjectId("5e2bfb1b71bf0181ecc422a0"), "EmployeeName" : "Chris" }
{ "_id" : ObjectId("5e2bfb1f71bf0181ecc422a1"), "EmployeeName" : "David" }