does mongodb have the properties such as trigger and procedure in a relational database?

Question

as the title suggests, include out the map-reduce framework if i want to trigger an event to run a consistency check or security operations before a record is inserted, how can i do that with MongoDB?

Answer 1

MongoDB does not support triggers, but people have created solutions around them, mostly using the oplog, though this will only help you if you are running with replica sets, as the oplog is a capped collection that keeps track of data changes for the purposes of replication. For a nodejs solution see: https://www.npmjs.org/package/mongo-watch or see an earlier SO thread: How to listen for changes to a MongoDB collection?

If you are concerned with consistency, read about write concern in mongoDB. http://docs.mongodb.org/manual/core/write-concern/ You can be as relaxed or as strict as you want by setting insert write concern levels, from fire and hope to getting an acknowledgement from all members of the replica set.

So, if you want to run a consistency check before inserting data, you probably will have to move that logic to the client application and set your write concern level to a level that will ensure consistency.

Answer 2

MongoDb does not have triggers or stored procedures. While there are solutions that some have used to try to emulate the behavior, as it is not a built-in feature, you'll need to decide whether the solutions are effective for you. Searching for "triggers and mongodb" should find dozens. All depend on the oplog and replicas.

But, given the nature of MongoDb and a typical 3 tier architecture, I would expect that at the point of data insertion, which could be on a web server for example, you would run, on the web server, the necessary consistency and security checks. You wouldn't allow a client such as a mobile application to directly set data into the database collection without some checks.

Many drivers for MongoDb and extended libraries have validation and consistency checks built in already, so there is less to do. Using unique indexes for some fields can also provide a level of consistency that you cannot do from the driver alone. Look at calls like findAndModify which make atomic updates.