用于访问文本文件的存储库模式

Question

我对存储库模式相当陌生，我想正确地做到这一点。我也在尝试使用控制反转（也是新的）。

我想确保我正确使用了存储库模式。

我选择它作为我的存储库的基本接口示例。

public interface IRepository<T> where T : class
{
    IEnumerable<T> Find(Expression<Func<T, bool>> where);

    IEnumerable<T> GetAll();

    void Create(T p);

    void Update(T p);
}

IPaymentRepository 用于 IRepository 的扩展（虽然我不明白如果我有上面的 Find 方法，我为什么需要它）

public interface IPaymentRepository : IRepository<Payment>
{
}

PaymentRepository 只是读取一个文本文件并构建一个 POCO。

public class PaymentRepository : IPaymentRepository
{
    #region Members

    private FileInfo paymentFile;
    private StreamReader reader;
    private List<Payment> payments;

    #endregion Members

    #region Constructors

    #endregion Constructors

    /// <summary>
    /// Initializes a new instance of the <see cref="PaymentRepository"/> class.
    /// </summary>
    /// <param name="paymentFile">The payment file.</param>
    public PaymentRepository(FileInfo paymentFile)
    {
        if (!paymentFile.Exists)
            throw new FileNotFoundException("Could not find the payment file to process.");

        this.paymentFile = paymentFile;
    }

    #region Properties

    #endregion Properties

    #region Methods

    public IEnumerable<Payment> Find(Expression<Func<Payment, bool>> where)
    {
        throw new NotImplementedException();
    }

    /// <summary>
    /// Gets all payments from payment file.
    /// </summary>
    /// <returns>Collection of payment objects.</returns>
    public IEnumerable<Payment> GetAll()
    {
        this.reader = new StreamReader(this.paymentFile.FullName);
        this.payments = new List<Payment>();

        while (!reader.EndOfStream)
        {
            string line = reader.ReadLine();
            Payment payment = new Payment()
            {
                AccountNo = line.Substring(0, 11),
                Amount = double.Parse(line.Substring(11, 10))
            };

            this.payments.Add(payment);
        }

        return this.payments;
    }

    public void Create(Payment p)
    {
        throw new NotImplementedException();
    }

    public void Update(Payment p)
    {
        throw new NotImplementedException();
    }

    #endregion Methods

我想知道如何实现 Find 方法。我假设我会调用 GetAll 并为存储库构建一个内部缓存。例如，我想查找所有付款超过 50 美元的帐户。

Answer 1

使用您当前的 IRepository 签名，您可以像这样实现它：

public IEnumerable<Payment> Find(Expression<Func<Payment, bool>> where)
{
    this.reader = new StreamReader(this.paymentFile.FullName);
    this.payments = new List<Payment>();

    while (!reader.EndOfStream)
    {
        string line = reader.ReadLine();
        Payment payment = new Payment()
        {
            AccountNo = line.Substring(0, 11),
            Amount = double.Parse(line.Substring(11, 10))
        };
        if (where(payment) 
        {
           this.payments.Add(payment);
        }
    }

    return this.payments;
}

但是，如果您的系统内存允许，您可以保留一个缓存列表（来自 GetAll()）并在该列表上使用 Find()。根据列表的大小，这应该快一个数量级。