Domain Layer + Repository Layer with asp.net mvc question

Just a quick question about my Domain Layer/ Domain Service... Should I allow this layer to have read only access to the database? i.e. hook up a IReadOnlySession and only allow the Repository Layer to have access to CRUD i.e. Persistence? Or should the Repository Layer do both the ReadOnly and CRUD with the service layer making 开发者_JAVA技巧a call to the Repository layer?

One thing I find rather strange is why most of the time the Service Layer is only making a direct call to the Repo, hence the question - move out ReadOnly to the Domain Service Layer.

EDIT:

I have decided to have 3 layers in my app (for anyone who is interested in what I have done), the first layer is the WebUI (I will have 3 in total, business requiement), below this is the Domain Service i.e. All business rules, validation, checking if user can do action x, user is valid user, calling the repo for the data. The final layer is the Repository Layer i.e. the layer that talks to the database iteself, I am using LinqToSql, all my CRUD and ReadOnly logic resides here. As a side note I created another project called Model, this is the actual LinqToSql model entities i.e. Product, Item, Shop, Customer etc. This very project is referenced by the UI, Domain Service and Repo, saving me from writing DTO, and from unecessary complexity hopefully.

In your application, only one 'layer' should talk to the database.

In the Repository pattern, it's the Repository.

It doesn't matter if it's CRUD or ReadOnly, it should go through the repository to the database.

I see the discussion as what are the responsibilities of these layers. The repository is clearly to provide an abstraction over the db. Done correctly and the users of the repository cannot tell if you are using SQL server, mysql or files for persistence. This layer must have all the necessary crud operations.

The service layer is another abstraction. It may depend upon the repository for persistence. There is usually a bit more business logic. Maybe cross repository concerns or another stream of data (gps for instance).

Some apps don't need a service layer. Don't add it until you need it. If you do have the need for the service layer, letting it be a thin rapper around the repo exposing read/write allows your models to only have one direct dependency.