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How to restrict inserting an item with the same name in MongoDB?
For this, use ensureIndex() and set unique:true. Let us create a collection with documents. Here, when we try to inert duplicate item, then a duplicate key error occurs −
> db.demo316.ensureIndex({"SubjectName":1},{unique:true}); { "createdCollectionAutomatically" : true, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 } > db.demo316.insertOne({"SubjectName":"MySQL"}); { "acknowledged" : true, "insertedId" : ObjectId("5e50e378f8647eb59e56205d") } > db.demo316.insertOne({"SubjectName":"MongoDB"}); { "acknowledged" : true, "insertedId" : ObjectId("5e50e37df8647eb59e56205e") } > db.demo316.insertOne({"SubjectName":"MongoDB"}); 2020-02-22T13:47:05.186+0530 E QUERY [js] WriteError: E11000 duplicate key error collection: test.demo316 index: SubjectName_1 dup key: { : "MongoDB" } : WriteError({ "index" : 0, "code" : 11000, "errmsg" : "E11000 duplicate key error collection: test.demo316 index: SubjectName_1 dup key: { : \"MongoDB\" }", "op" : { "_id" : ObjectId("5e50e381f8647eb59e56205f"), "SubjectName" : "MongoDB" } }) 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
Display all documents from a collection with the help of find() method −
> db.demo316.find();
This will produce the following output −
{ "_id" : ObjectId("5e50e378f8647eb59e56205d"), "SubjectName" : "MySQL" } { "_id" : ObjectId("5e50e37df8647eb59e56205e"), "SubjectName" : "MongoDB" }
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