如何从MongoDB集合中删除重复项
db.yourCollectionName.ensureIndex({yourFieldName: 1}, {unique: true, dropDups: true})为了理解上述语法，让我们创建一个包含文档的集合。在这里，不允许重复插入-
> db.demo604.ensureIndex({FirstName: 1}, {unique: true, dropDups: true});{
"createdCollectionAutomatically" : true,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
> db.demo604.insertOne({FirstName:"Chris"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e960887ed011c280a0905d8")
}
> db.demo604.insertOne({FirstName:"Bob"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e96088aed011c280a0905d9")
}
> db.demo604.insertOne({FirstName:"David"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e96088ded011c280a0905da")
}
> db.demo604.insertOne({FirstName:"Chris"});
2020-04-15T00:31:35.978+0530 E QUERY [js] WriteError: E11000 duplicate key error collection: test.demo604 index: FirstName_1 dup key: { : "Chris" } :
WriteError({
"index" : 0,
"code" : 11000,
"errmsg" : "E11000 duplicate key error collection: test.demo604 index: FirstName_1 dup key: { : \"Chris\" }",
"op" : {
"_id" : ObjectId("5e96088fed011c280a0905db"),
"FirstName" : "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.demo604.find();
这将产生以下输出-
{ "_id" : ObjectId("5e960887ed011c280a0905d8"), "FirstName" : "Chris" }
{ "_id" : ObjectId("5e96088aed011c280a0905d9"), "FirstName" : "Bob" }
{ "_id" : ObjectId("5e96088ded011c280a0905da"), "FirstName" : "David" }