创建上下文对象

///

/// 负责创建EF上下文对象，保证线程内唯一，在一次请求内，只创建一次该对象
///

public class DbContextFactory
{

    public static DbContext GetCurrentDbContext()
    {
        DbContext dbContext = (DbContext)CallContext.GetData("dbContext");
        if(dbContext==null)
        {
            dbContext = new book_shopEntities();
            CallContext.SetData("dbContext", dbContext);
        }
        return dbContext;
    }
}