C# Linq-to-SQL Create a Generic Repository

Question

I have a few repositories that all generally look like this

public class DepartmentsRepository
{
    private PersonnelActionFormDataContext db = new PersonnelActionFormDataContext();

    /// <summary>
    /// returns all departments
    /// </summary>
    /// <returns>an iquerable of all departments</returns>
    public IQueryable<Department> GetAll()
    {
        return db.Departments;
    }

    /// <summary>
    /// Get department by id
    /// </summary>
    /// <param name="id">id of the department</param>
    /// <returns>a null department if nothing is found</returns>
    public Department Get(int id)
    {
        return db.Departments.SingleOrDefault(d => d.id == id);
    }

    /// <summary>
    /// Get department by department name
    /// </summary>
    /// <param name="department">name of the department</param>
    /// <returns>a null department if nothing is found</returns>
    public Department Get(string department)
    {
        return db.Departments.SingleOrDefault(d => d.DepartmentName == department);
    }

    /// <summary>
    /// Add a department
    /// </summary>
    /// <param name="department"></param>
    public void Add(Department department)
    {
        db.Departments.InsertOnSubmit(department);
    }

I'd like to have some sort of generic base class that could save me some typing, so I started here

 public class GenericRepository<T>
{
    private PersonnelActionFormDataContext db = new PersonnelActionFormDataContext();

    public IQueryable<T> GetAll()
    {
        return db.
    }
}

how do I access the collection of Ts to return them? Is this possible?

Thanks for the help.

what is db - is this linq-to-sql, or entity framework?

Adam Rackis
– Adam Rackis

2011-02-23 20:22:01 +00:00
Commented Feb 23, 2011 at 20:22 — Adam Rackis
– Adam Rackis, Commented Feb 23, 2011 at 20:22
That actually makes it easier - see my updated answer

Adam Rackis
– Adam Rackis

2011-02-23 20:30:15 +00:00
Commented Feb 23, 2011 at 20:30 — Adam Rackis
– Adam Rackis, Commented Feb 23, 2011 at 20:30

Adam Rackis · Accepted Answer · 2011-03-09 19:16:49Z

3

For Linq-to-SQL this should work:

public IQueryable<T> GetResultL2S<T>() where T : class {
    MyDataContext db = new MyDataContext();
    return db.GetTable<T>();
}

Or, if you're using Entity Framework, then you'd do something like:

public IQueryable<T> GetResultEF<T>() {
    YourEntities db = new YourEntities();
    return db.CreateQuery<T>(String.Format("[{0}s]", typeof(T).Name));
}

That assumes your entity sets can be pluralized by tacking an s on. If that's not the case, then check out System.Data.Entity.Design.PluralizationServices.PluralizationService

edited Mar 9, 2011 at 19:16

answered Feb 23, 2011 at 20:23

Adam Rackis

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12 Comments

jim Over a year ago

public T Get<T>(int id) where T : class { return db.GetTable<T>().SingleOrDefault(d => d.id == id); } something like this doesn't work. Any ideas?

Adam Rackis Over a year ago

How could it? C# doesn't know that whatever T is has an id property on it. You'd have to say where T : class, ISomeInterfaceWithAnIdPropertyOnIt

Adam Rackis Over a year ago

Or if an interface like that's not available, you'd have to build an expression tree from scratch, which can get obtuse. Here's a simple example (tested only with EF, not L2S) stackoverflow.com/questions/5046917/…

jim Over a year ago

AHHH, good looking out. OK...so, do I have to do something like create partial classes for my dbcontext objects and then and implement a iEntity with a id property and then do something like this, where T : iEntity...then these will work. Is there a better way?

Chris Sainty Over a year ago

Here is a generic primary key function for L2S that I wrote a while back if you are having trouble converting the EF one. http://csainty.blogspot.com/2008/04/linq-to-sql-generic-primary-key.html

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