在MongoDB中使用索引防止多个字段重复
为防止多个字段重复，请使用sureIndex()并设置unique：true。让我们创建一个包含文档的集合-
> db.demo272.ensureIndex({"FirstName":1,"Subject":1},{unique:true});
{
"createdCollectionAutomatically" : true,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
> db.demo272.insertOne({"FirstName":"Chris","Subject":"MySQL"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e48232a1627c0c63e7dbabf")
}
> db.demo272.insertOne({"FirstName":"Chris","Subject":"MongoDB"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e48232f1627c0c63e7dbac0")
}
> db.demo272.insertOne({"FirstName":"David","Subject":"MySQL"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e48233a1627c0c63e7dbac1")
}
> db.demo272.insertOne({"FirstName":"Chris","Subject":"MySQL"});
2020-02-15T22:28:55.137+0530 E QUERY [js] WriteError: E11000 duplicate key error collection: test.demo272 index: FirstName_1_Subject_1 dup key: { : "Chris", : "MySQL" } :
WriteError({
"index" : 0,
"code" : 11000,
"errmsg" : "E11000 duplicate key error collection: test.demo272 index: FirstName_1_Subject_1 dup key: { : \"Chris\", : \"MySQL\" }",
"op" : {
"_id" : ObjectId("5e48234f1627c0c63e7dbac2"),
"FirstName" : "Chris",
"Subject" : "MySQL"
}
})
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.demo272.find();
这将产生以下输出-
{ "_id" : ObjectId("5e48232a1627c0c63e7dbabf"), "FirstName" : "Chris", "Subject" : "MySQL" }
{ "_id" : ObjectId("5e48232f1627c0c63e7dbac0"), "FirstName" : "Chris", "Subject" : "MongoDB" }
{ "_id" : ObjectId("5e48233a1627c0c63e7dbac1"), "FirstName" : "D
okavid", "Subject" : "MySQL" }