在Entity Framework Core上使用using（）封装DbContext

Question

I wanted to try to expose a DbContext instance through a get statement:

public class SomeContext : DbContext
{
    public SomeContext()
    {

    }

    public DbSet<SomeModel1> SomeModel1s { get; set; }
    public DbSet<SomeModel2> SomeModel2s { get; set; }

   //etc
}

public class SomeInterfaceImplementation
{
    SomeContext ContextInstance { get; }
    //etc
}

But instead of using ContextInstance as a singleton, I want to do something so that calling ContextInstance actually does something like:

someVar = ContextInstance.SomeModel1s.Where(x => x.SomeID == externalID).OrderBy(x => x.SomeProperty).ToList();
//becomes the same as
using (var db = new SomeContext())
{
  someVar = db.SomeModel1s.Where(x => x.SomeID == externalID).OrderBy(x => x.SomeProperty).ToList();
}

basically, I just want to hide the using statement and create and dispose an instance of SomeContext every time ContextInstance is called. Hopefully I make sense. Does anyone have something in mind to do this?

Answer 1

This may not be a very good idea, because there are some standard scenarios with DbContext . For example DbContext implements Unit of Work pattern so the using may be necessary.

But you can make what you want although is't not easy.

You need implement IQueryProvider<TEntity> interface and especially the generic method Execute :

public class EFDbSetProvider<TEntity> : IQueryableProvider<TEntity>
where TEntity : class
{
    public TResult Execute<TResult>(Expression expression)
    {
        using (dbContext = new DbContext())
        {
             return (TResult) dbContext.Set<TEntity>.Provider.Execute(expression);
        }
    }
}

Also you'll need implement corresponding IQueryable<TEntity> interface, but as I can see this implementation should be very simple.

public class EFQueryable<TEntity> : IQueryable<TEntity>
{
    . . .
}

public static class SomeContext
{
    public static EFQueryable<SomeModel1> SomeModels1 { get; set; }
    public static EFQueryable<SomeModel2> SomeModels2 { get; set; }
}

someVar = SomeContext.SomeModel1s.Where(x => x.SomeID == externalID).OrderBy(x => x.SomeProperty).ToList();

The Execute method will be called from ToList , then it will create DbContext and pass the assemblied expression to DbSet<TEntity>.Provider.Execute .

You may google "custom LINQ providers" or "IQueryable implementation example". Fe I found the article Implementing a ustom LINQ provider so you can start here for details.