Is an ORM redundant with a NoSQL API?

Question

with MongoDB (and I assume other NoSQL database APIs worth their salt) the ways of querying the database are much more simplistic than SQL. There is no tedious SQL queries to generate and such. For instance take this from mongodb-csharp:

using MongoDB.Driver; 
Mongo db = new Mongo(); 
db.Connect(); //Connect to localhost on the default port. 
Document query = new Document(); 
query["field1"] = 10; 
Document result = db["tests"]["reads"].FindOne(query); 
db.Disconnect();

How could an ORM even simplify that? Is an ORM or other "database abstraction device" required on top of a decent NoSQL API?

Solution 1

Well, yes, Object-Relational mappers are redundant with MongoDB because MongoDB isn't a relational database, it's a Document-Oriented database.

So instead of SQL, you write queries in JSON. Unless you really, really want to write raw JSON, as opposed to, say, Linq, then you're still going to want to use a mapper. And if you don't want to create coupling against MongoDB itself, then you don't want to pass actual Document objects around, you want to map them to real POCOs.

The mapping is much easier with a document-oriented DB like MongoDB, because you have nested documents instead of relations, but that doesn't mean it goes away completely. It just means you've substituted one type of "impedance mismatch" for a different, slightly-less-dramatic mismatch.

Solution 2

I think an "ORM" on MongoDb can be useful, not only for "serializing" and "deserializing" objects into the db (Norm seems to do a great job) but also for making it more easy to execute aggregation queries.

It is nice if an "ORM" can generate MapReduce jobs for grouping and detecting duplicates. Some people have written code to automatically convert an sql statement into a mapreduce job: http://rickosborne.org/blog/index.php/2010/02/19/yes-virginia-thats-automated-sql-to-mongodb-mapreduce/

Solution 3

Take a look on Kundera : https://github.com/impetus-opensource/Kundera, ORM over mongodb, cassandra, HBase.

Solution 4

Another solution is PlayOrm which can do joins as well when necessary with it's Scalable-SQL language(just adds a prefix to normal SQL basically to add partition info).

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Comments

[Aaronaught]

Who calls NoRM an ORM? I thought it was a recursive acronym for " Not an Object Relational Mapper." Or maybe it's just "Not a Relational Mapper", since the "o" is lowercase. Either way, it's definitely not an ORM!

[Aaronaught]

@Cocowalla: I think NoRM is the only one that's really worth the bother at the moment. That may change in a year or two.

[Marchy]

Your answer dodges the problem that the question asks about - which is to understand the need for a higher-level abstraction that an ORM provides. Just like RDBMS's, document-oriented databases need to store relations between entities. As stated in the MongoDB intro docs (docs.mongodb.org/manual/core/data-modeling-introduction), you need to choose between embedding related data or referencing other documents. Related documents need subsequent queries, similar to lazy loading in Entity Framework. An ORM would be helpful in simplifying this, just as EF simplifies SQL joins.

[Aaronaught]

@Marchy: I wasn't "dodging" anything, and I don't agree that abstracting this away in MongoDB would be a good idea, as it would encourage developers to model data in a relational fashion when proper data modeling is the most crucial concern - as the very page you linked to clearly points out. Loading related documents one-by-one can kill performance, when most such databases have first-class support for minimizing round trips. Some, like RavenDB, even support query batching and relation-loading, which makes automatic lazy loading an even worse idea. I would not want to see that kind of "ORM".

[geoidesic]

@Aaronaught Using an ORM is never optimally efficient, not even for SQL. That's not the point of an ORM. The point is to make it easy to deal with data (and security) via objects. If you want optimal, you always have to write native queries unless you're doing something incredibly simple.