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Avoid duplicate entries in MongoDB?
To avoid duplicate entries in MongoDB, you can use createIndex(). The syntax is as follows −
db.yourCollectionName.createIndex({"yourFieldName":1},{unique:true});Let us implement the above syntax. The query to avoid duplicate entries in MongoDB is a follows −
> db.avoidDuplicateEntriesDemo.createIndex({"UserName":1},{unique:true});
{
"createdCollectionAutomatically" : true,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}Now insert some records in the above collection. The query to insert record is as follows −
> db.avoidDuplicateEntriesDemo.insertOne({"UserName":"John"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90e1824afe5c1d2279d697")
}Here is the error whenever you try to insert the same record once again −
> db.avoidDuplicateEntriesDemo.insertOne({"UserName":"John"});
2019-03-19T18:03:08.465+0530 E QUERY [js] WriteError: E11000 duplicate key error collection: test.avoidDuplicateEntriesDemo index: UserName_1 dup key: { : "John" } :
WriteError({
"index" : 0,
"code" : 11000,
"errmsg" : "E11000 duplicate key error collection: test.avoidDuplicateEntriesDemo index: UserName_1 dup key: { : \"John\" }",
"op" : {
"_id" : ObjectId("5c90e1844afe5c1d2279d698"),
"UserName" : "John"
}
})
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):1:1Let us insert another record. The query is as follows −
> db.avoidDuplicateEntriesDemo.insertOne({"UserName":"Carol"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90e18d4afe5c1d2279d699")
}Display all documents from a collection with the help of find() method. The query is as follows −
> db.avoidDuplicateEntriesDemo.find();
The following is the output −
{ "_id" : ObjectId("5c90e1824afe5c1d2279d697"), "UserName" : "John" }
{ "_id" : ObjectId("5c90e18d4afe5c1d2279d699"), "UserName" : "Carol" }
Updated on: 30-Jul-2019
912 Views
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