实体框架 - 查询适配器

Question

我正在为实体框架而苦苦挣扎，我在其中创建了一个包含在整个系统中使用的业务对象（即帐户）的库。

public class Account
{
    public long AccountId { get; set; }
    public string AccountText { get; set; }
}

实体框架会在请求或需要保存时来回转换它们

public interface EntityAdapter<T> {
    T Materialize(long id);

    long Dematerialize(T business);
    void Dispose(T business);
}

public abstract class EFEntityAdapter<T> : EntityAdapter<T> {
    private static MyModel.MyEntities __ctx = null;
    protected MyModel.MyEntities _context
    {
        get
        {
            if (__ctx == null)
            {
                __ctx = new MyModel.MyEntities ();
            }
            return __ctx;
        }
    }

    public abstract T Materialize(long id);
    public abstract long Dematerialize(T business);
    public abstract void Dispose(T business);
}
public class AccountEntityAdapter : EFEntityAdapter<CommonLib.BusinessModels.Account>
{
    public override CommonLib.BusinessModels.Account Materialize(long id)
    {
        Account entity = (from account in _context.Accounts
                          where account.AccountId == id
                          select account).FirstOrDefault();

        if (entity == null)
            return null;

        CommonLib.BusinessModels.Account business = new CommonLib.BusinessModels.Account();

        business.AccountId = entity.AccountId;
        business.AccountText = entity.AccountText;

        return business;
    }

    public override long Dematerialize(CommonLib.BusinessModels.Account business)
    {
        long id = business.AccountId;

        Account entity = (from account in _context.Accounts
                          where account.AccountId == id
                          select account).FirstOrDefault();

        if (entity == null)
        {
            if (id > 0)
            {
                throw new Exception("Account with id: " + id + " does not exists");
            }
            else
            {
                entity = new Account();
                _context.Accounts.AddObject(entity);
            }
        }

        entity.AccountId = business.AccountId;
        entity.AccountText = business.AccountText;
        _context.SaveChanges();
        business.AccountId = entity.AccountId;
        return entity.AccountId;
    }

    public override void Dispose(CommonLib.BusinessModels.Account business)
    {
        long id = business.AccountId;

        Account entity = (from account in _context.Accounts
                          where account.AccountId == id
                          select account).FirstOrDefault();

        if (entity == null)
        {
            throw new Exception("Account with id: " + id + " was not found, but an attempt to delete it was done");
        }

        _context.DeleteObject(entity);
        _context.SaveChanges();
    }
}

但现在我想将适配器与 linq 一起使用，这样我就可以做类似的事情

AccountEntityAdapter a = new AccountEntityAdapter();
List<Commonlib.BusinessModels.Account> list = (from account in a
                                               where account.AccountId > 6
                                               select account).ToList();

这样我就摆脱了实体上下文...

我怎样才能做到这一点？

Answer 1

根据您的 cmets，您的选择是：

• 直接在 linq-to-entities 查询中进行投影，而不是使用映射器
• 查询您的实体，调用 .ToList 并对结果运行 linq-to-object 查询，并使用您的映射器进行投影

Answer 2

您需要一个上下文来连接到您的数据库。然而，这通常被封装在一个存储库中并包含在一个中心位置以供使用，而不是为每个操作创建一个上下文。