Entity Framework Generics

Question

Background:

Whilst writing my own MVC application I had a requirement to interact with a database. I decided to use generics with entity framework Repositories like so:

    public class Repository<TEntity> : IRepository<TEntity> where TEntity : class
{
    DatabaseContext<TEntity> _dbContext;
    Database _database;

    public IQueryable<TEntity> All
    {
        get
        {
            return (IQueryable<TEntity>) _dbContext.Items;
        }
    }

    public Repository()
    {
        _dbContext = new DatabaseContext<TEntity>();
        _database = _dbContext.Database;
    }
}

As you can see I also use a generic DbContext.

My Two Part Question

I took a while to sit back and look at the solution before proceeding with it. I realise that this forces me to create multiple DB context objects.

i) Is this bad practice?

ii) Will it have a noticeable impact on the efficiency of my solution?

Well if you use generics for the contect object like the code above then you would need to create multiple dbcontexts (one for each entity). So you would have one repository per entity and one DbContext per entity also. — K-Dawg
– K-Dawg, Commented Oct 12, 2015 at 9:57

DavidG · Accepted Answer · 2015-10-12 10:08:00Z

2

First of all there is no need to have a generic context. You can use the Set<> property of your context object. I would also not create the context object inside the repository. Instead pass it in the constructor as this will allow you to inject it in other ways, and reuse it in other projects later on.

So your repository could look like this:

public class Repository<TEntity> : IRepository<TEntity> where TEntity : class
{
    private DbContext _context;

    public Repository(DbContext context)
    {
        _context = context;
    }

    public IQueryable<TEntity> All
    {
        get
        {
            return _context.Set<TEntity>();
        }
    }

}

You could even do this without having the repository as generic and instead just making the individual methods generic, for example:

public IQueryable<TEntity> All<TEntity> where TEntity : class
{
    get
    {
        return _context.Set<TEntity>();
    }
}

answered Oct 12, 2015 at 10:08

DavidG

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4 Comments

K-Dawg Over a year ago

Ah thanks for that! I thought I was injecting the context in but I'd forgotten that I'd put that in there temporarily and forgotten about it.

K-Dawg Over a year ago

Ah yes generic methods and properties!

DavidG Over a year ago

So does this do the job for you? I know it's not quite what you asked but rather a different way of doing it.

K-Dawg Over a year ago

Hi David, I appreciate the alternative. I'm currently trying it out.

DavidG · Accepted Answer · 2015-10-12 10:30:31Z

1

Multiple db context(leads to creating multiple database) are created because every generic context is treated as new database connection.

We have multiple dbContext which can target one database. It can be achieved as below

Create DbContext(generic one in your case)

public class HumanResourceContext : BaseContext<HumanResourceContext>
{
    //DbSet properties
}

public class SalesContext : BaseContext<SalesContext>
{
//DbSet properties
}

Create class called "BaseContect" and copy this code

public class BaseContext<TContext>
    : DbContext where TContext : DbContext
{
    static BaseContext()
    {
        //By setting it NULL, we are making it work with Existing Adventure Works database
        Database.SetInitializer<TContext>(null);
    }
    protected BaseContext()
        : base("name=AdventureWorksContext") //Points to Connection String in Config file
    { }
}

This will help create multiple DbContext which targets one database, this is proper way to do it.

edited Oct 12, 2015 at 10:30

DavidG

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answered Oct 12, 2015 at 10:24

Mithun Pattankar

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1 Comment

DavidG Over a year ago

Fixed your formatting (in a numbered list, code is created by prefixing it with 8 spaces).

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