Is Dataset an ORM?

Question

I am a little bit confused about Dataset compared to ORM (NHibernate or Spring.Net). From my understanding the ORM sits between the application layer and the database layer. It will generate the SQL commands for the application layer. Is this the same as what Dataset does? What is the difference between the Dataset and ORM? What are the advantages and disadvantages for these two methods? Hope the experts in here can explain something.

Thanks, Fakhrul

Answer 1

There is a BIG difference between them, first of all about the programming model they represent:

1. The Dataset is based on a Table Model
2. An ORM (without specify a particular product of framework) is based and tends to a Domain Model.
3. There is another kind of tool which could be used in data scenario, this kind of tool is a Data Mapper (eg. iBatis.NET)

As others answers before me, I think it's important to view what Microsoft says about Dataset and better what Wikipedia says about ORM, but I think (this was for me at beginning) it's more to understand the difference between them in terms of model. Understanding that will not only clarify the choises behind but better, will do too easy to approach and understand a tool itself.

As little explanation it's possible to say:

Table Model

is a model which tends to represent tabular data in a memory structure as close as possible (and even as needed). So it's easy to find implementations which implements concepts as Table, Columns, Relations in fact the model is concetrate on the table structure, so object orientation is based on that not on data itself. This model could has its own advantages, but in some case could be heavy to manage and difficult to apply concepts on contained data. As previous answers says, implementations like Dataset, let, or better, force you to prepare (even if with a tool) needed SQL instructions to perform actions over the data.

ORM

is a model which (as mendelt says before me..) where Objects are mapped directly to database objects, principally Tables and Views (even if it's possible to map even functions and procedures too). This is done in 2 ways generally, with a mapping file which describes the mapping, or with (in case of .NET or Java) code Attributes. This model is based on Objects which represents the data, so object orientation could be done on them as in normal programs, it's clear with more attention and caution in certain cases, but generally, when you are confident with ORM it could be a really powerfull tool! Even ORM could be heavy to manage if it's not managed and designed well, or better understood weel, so it's important to understand techniques, but I can say with my experience that ORM is a really powerfull tool. In ORM, the tool principally it's responsible to generate the SQL instructions needed as operations are done in code, and in more cases ORMs has a middle language (like HQL) to perform operations on Objects.

MAPPER

A mapper is a tool which doesn't makes things like an ORM, but, maps hand written SQL instructions to an Object Model. Thi kind of tool could be a better solution when it's needed to write by hand SQL instructions but It's wanted to designe an application Object model to represent data. In this "model" objects are mapped to instruction and described in a mapping file (generally an Xml file as iBatis.Net or iBATIS (java) does). A mapper let you define granular rules in SQL instructions. In this scenario could be easy to find some ORM concepts as for example session management.

ORM and Mappers let to apply some very interesting Design Patterns, which could be not so easy to apply in the same way to a Table Model and in this case to a Dataset.

First of all excuse me for this long answer and about my poor english, but for me, an answer like this makes me in past to understand well the difference between this models and then between implementations.

Answer 2

the Dataset class is definitly not an ORM; an ORM maps relational data with an object oriented representation.

It can be regarded as some kind of 'unit of work' though, since it keeps track of the rows that have to be deleted/updated/inserted.

Answer 3

• ADO.NET DataSet =

  http://msdn.microsoft.com/en-us/library/zb0sdh0b(VS.80).aspx

• ORM =

  http://en.wikipedia.org/wiki/Object-relational_mapping (Example Developer Express XPO,DataObjects.NET)