零、前言

　　之前寫一些小工具的時候，需要用到數據存儲方面的技術，但是用數據庫又覺得太大了，本地文件存儲txt文件存儲又不是很規範，於是乎想到了去編寫一個簡單的基於本地文件系統的數據存儲庫，暫且叫它localdb吧，總之也是為了方便使用，特別是數據量不大，但是又特別想要本地數據存儲的。（拋開access不說）

一、工具

　　工欲善其事必先利其器，存儲數據必然要有一個標準的數據格式，首先讓我想到的就是json,xml，原因不必多說。所以下面編寫的數據主要以json作為存儲格式。json操作用Newtonjson，操作方便簡單。

二、文件系統的操作（LocalFileDB）

　　本地數據庫，必不可少對本地文件進行操作，所以對本地文件的讀取創建統一管理，話不多說，直接上代碼。

　　首先添加自定義的異常：

    /// <summary>
    /// 文件數據庫異常
    /// </summary>
    public class FileDatabaseException : Exception
    {
        public FileDatabaseException(string message)
            : base(message)
        { }

        public FileDatabaseException(string message, Exception innerException)
            : 
 
base(message, innerException)
        { }
    }

　　然後是具體操作文件的代碼（這塊有參考別人的，僅供學習使用，如有侵權，請聯系我）：

    /// <summary>
    /// 文件數據庫，這是一個抽象類。(之前做的拿來用的，也可以應用於xml,但已有linq to xml，所以這邊暫時僅用於json)
    /// </summary>
    public abstract class FileDatabase<TEntity>
    {
        #region Fields

        ///
 
 <summary>
        /// 文件數據庫操作鎖
        /// </summary>
        protected static readonly object operationLock = new object();
        private static HashSet<char> invalidFileNameChars;

        static FileDatabase()
        {
            invalidFileNameChars = new HashSet<char>() { ‘\0‘, ‘ ‘, ‘.‘, ‘$‘, ‘/‘, ‘\\‘ };
            foreach (var c in Path.GetInvalidPathChars()) { invalidFileNameChars.Add(c); }
            foreach (var c in Path.GetInvalidFileNameChars()) { invalidFileNameChars.Add(c); }
        }

        /// <summary>
        /// 文件數據庫
        /// </summary>
        /// <param name="directory">數據庫文件所在目錄</param>
        protected FileDatabase(string directory)
        {
            MyDirectory = directory;
        }

        public FileDatabase()
        {

        }

        #endregion

        #region Properties

        /// <summary>
        /// 數據庫文件所在目錄
        /// </summary>
        public virtual string MyDirectory { get; protected set; }

        /// <summary>
        /// 文件擴展名
        /// </summary>
        public virtual string FileExtension { get; set; }

        public virtual bool IsIndent { get; set; }

        #endregion

        #region Public Methods

        /// <summary>
        /// 保存文檔
        /// </summary>
        /// <typeparam name="TEntity">文檔類型</typeparam>
        /// <param name="id">文檔ID</param>
        /// <param name="document">文檔對象</param>
        /// <returns>文檔ID</returns>
        public virtual string Save(string id, TEntity document)
        {
            if (string.IsNullOrEmpty(id))
                throw new ArgumentNullException("id");

            if (document == null)
                throw new ArgumentNullException("document");

            Delete(id);

            try
            {
                string fileName = GenerateFileFullPath(id);
                string output = Serialize(document, IsIndent);

                lock (operationLock)
                {
                    System.IO.FileInfo info = new System.IO.FileInfo(fileName);
                    System.IO.Directory.CreateDirectory(info.Directory.FullName);
                    System.IO.File.WriteAllText(fileName, output);
                }
            }
            catch (Exception ex)
            {
                throw new FileDatabaseException(
                  string.Format(CultureInfo.InvariantCulture,
                  "Save document failed with id [{0}].", id), ex);
            }

            return id;
        }

        /// <summary>
        /// 根據文檔ID查找文檔
        /// </summary>
        /// <typeparam name="TEntity">文檔類型</typeparam>
        /// <param name="id">文檔ID</param>
        /// <returns>文檔對象</returns>
        public virtual TEntity FindOneById(string id)
        {
            if (string.IsNullOrEmpty(id))
                throw new ArgumentNullException("id");

            try
            {
                string fileName = GenerateFileFullPath(id);
                if (File.Exists(fileName))
                {
                    string fileData = File.ReadAllText(fileName);
                    return Deserialize(fileData);
                }

                return default(TEntity);
            }
            catch (Exception ex)
            {
                throw new FileDatabaseException(
                  string.Format(CultureInfo.InvariantCulture,
                  "Find document by id [{0}] failed.", id), ex);
            }
        }

        /// <summary>
        /// 查找指定類型的所有文檔
        /// </summary>
        /// <typeparam name="TEntity">文檔類型</typeparam>
        /// <returns>文檔對象序列</returns>
        public virtual IEnumerable<TEntity> FindAll()
        {
            try
            {
                List<TEntity> list = new List<TEntity>();

                if (Directory.Exists(GenerateFilePath()))
                {
                    string[] files = System.IO.Directory.GetFiles(
                      GenerateFilePath(),
                      "*." + FileExtension,
                      SearchOption.TopDirectoryOnly);

                    foreach (string fileName in files)
                    {
                        string fileData = File.ReadAllText(fileName);
                        TEntity document = Deserialize(fileData);
                        if (document != null)
                        {
                            list.Add(document);
                        }
                    }
                }

                return list;
            }
            catch (Exception ex)
            {
                throw new FileDatabaseException(
                  "Find all documents failed.", ex);
            }
        }

        /// <summary>
        /// 根據指定文檔ID刪除文檔
        /// </summary>
        /// <typeparam name="TEntity">文檔類型</typeparam>
        /// <param name="id">文檔ID</param>
        public virtual void Delete(string id)
        {
            if (string.IsNullOrEmpty(id))
                throw new ArgumentNullException("id");

            try
            {
                string fileName = GenerateFileFullPath(id);
                if (File.Exists(fileName))
                {
                    lock (operationLock)
                    {
                        File.Delete(fileName);
                    }
                }
            }
            catch (Exception ex)
            {
                throw new FileDatabaseException(
                  string.Format(CultureInfo.InvariantCulture,
                  "Delete document by id [{0}] failed.", id), ex);
            }
        }

        /// <summary>
        /// 刪除所有指定類型的文檔
        /// </summary>
        /// <typeparam name="TEntity">文檔類型</typeparam>
        public virtual void DeleteAll()
        {
            try
            {
                if (Directory.Exists(GenerateFilePath()))
                {
                    string[] files = System.IO.Directory.GetFiles(
                      GenerateFilePath(), "*." + FileExtension,
                      SearchOption.TopDirectoryOnly);

                    foreach (string fileName in files)
                    {
                        lock (operationLock)
                        {
                            File.Delete(fileName);
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                throw new FileDatabaseException(
                  "Delete all documents failed.", ex);
            }
        }

        /// <summary>
        /// 獲取指定類型文檔的數量
        /// </summary>
        /// <typeparam name="TEntity">文檔類型</typeparam>
        /// <returns>文檔的數量</returns>
        public virtual int Count()
        {
            try
            {
                if (Directory.Exists(GenerateFilePath()))
                {
                    string[] files = System.IO.Directory.GetFiles(
                      GenerateFilePath(),
                      "*." + FileExtension, SearchOption.TopDirectoryOnly);
                    if (files != null)
                    {
                        return files.Length;
                    }
                    else
                    {
                        return 0;
                    }
                }
                return 0;
            }
            catch (Exception ex)
            {
                throw new FileDatabaseException(
                  "Count all documents failed.", ex);
            }
        }

        #endregion

        #region Protected Methods

        /// <summary>
        /// 生成文件全路徑
        /// </summary>
        /// <typeparam name="TEntity">文檔類型</typeparam>
        /// <param name="id">文檔ID</param>
        /// <returns>文件路徑</returns>
        protected virtual string GenerateFileFullPath(string id)
        {
            return Path.Combine(GenerateFilePath(),
              GenerateFileName(id));
        }

        /// <summary>
        /// 生成文件路徑
        /// </summary>
        /// <typeparam name="TEntity">文檔類型</typeparam>
        /// <returns>文件路徑</returns>
        protected virtual string GenerateFilePath()
        {
            return Path.Combine(this.MyDirectory, typeof(TEntity).Name);
        }

        /// <summary>
        /// 生成文件名
        /// </summary>
        /// <typeparam name="TEntity">文檔類型</typeparam>
        /// <param name="id">文檔ID</param>
        /// <returns>文件名</returns>
        protected virtual string GenerateFileName(string id)
        {
            if (string.IsNullOrEmpty(id))
                throw new ArgumentNullException("id");

            foreach (char c in id)
            {
                if (invalidFileNameChars.Contains(c))
                {
                    throw new FileDatabaseException(
                      string.Format(CultureInfo.InvariantCulture,
                      "The character ‘{0}‘ is not a valid file name identifier.", c));
                }
            }

            return string.Format(CultureInfo.InvariantCulture, "{0}.{1}", id, FileExtension);
        }

        /// <summary>
        /// 將指定的文檔對象序列化至字符串
        /// </summary>
        /// <param name="value">指定的文檔對象</param>
        /// <returns>文檔對象序列化後的字符串</returns>
        protected abstract string Serialize(object value, bool isIndent = false);

        /// <summary>
        /// 將字符串反序列化成文檔對象
        /// </summary>
        /// <typeparam name="TEntity">文檔類型</typeparam>
        /// <param name="data">字符串</param>
        /// <returns>文檔對象</returns>
        protected abstract TEntity Deserialize(string data);

        #endregion
    }

三、存儲架構的設計

1、基礎設施的構建

　　數據庫采用的是類似倉儲的設計，這樣對數據的管理比較直觀，並且易用。什麽是倉儲，園內有很多博客有闡述，在此就不贅述了。

　　首先，要先有實體基類：

    /// <summary>
    ///     可持久到數據庫的領域模型的基類。
    /// </summary>
    [Serializable]
    public abstract class EntityBase
    {
        #region 構造函數

        /// <summary>
        ///     數據實體基類
        /// </summary>
        protected EntityBase()
        {
        }

        #endregion
    }

　　其次，要有倉儲接口：

    /// <summary>
    /// 數據基礎操作規範
    /// </summary>
    /// <typeparam name="TEntity"></typeparam>
    public interface IRepository<TEntity> 
        where TEntity : EntityBase
    {
        /// <summary>
        /// 添加實體並提交到數據服務器
        /// </summary>
        /// <param name="item">需要添加數據項</param>
        /// <returns>受影響條數</returns>
        int Insert(TEntity item);

        /// <summary>
        /// 移除實體並提交到數據服務器
        /// 如果表存在約束，需要先刪除子表信息
        /// </summary>
        /// <param name="item">需要刪除的數據項</param>
        /// <returns>受影響條數</returns>
        int Delete(TEntity item);

        /// <summary>
        /// 修改實體並提交到數據服務器
        /// </summary>
        /// <param name="item">需要修改的數據項</param>
        /// <returns>受影響條數</returns>
        int Update(TEntity item);

        /// <summary>
        /// 得到指定的實體集合（延時結果集）
        /// </summary>
        /// <returns>實體集合</returns>
        IQueryable<TEntity> GetModel();

        /// <summary>
        /// 根據主鍵得到實體
        /// </summary>
        /// <param name="id"></param>
        /// <returns></returns>
        TEntity Find(params object[] id);
    }

2、基於json倉儲的實現

　　json實體基類：

    /// <summary>
    /// Json實體基類
    /// </summary>
    public abstract class JsonEntity : EntityBase
    {
        private string id = PublicHelper.GuidGenerator();
        /// <summary>
        /// Json實體主鍵
        /// </summary>
        public string RootID
        {
            get { return id; }
            set { id = value; }
        }
    }

　　json倉儲接口：

    /// <summary>
    /// Json倉儲接口
    /// </summary>
    /// <typeparam name="TEntity"></typeparam>
    public interface IJsonRepository<TEntity>
        : IRepository<TEntity>
        where TEntity : JsonEntity
    {
        /// <summary>
        /// 是否縮進
        /// </summary>
        bool IsIndent { get; set; }
        /// <summary>
        /// 按文件存儲，直接刪除所有文件
        /// </summary>
        void DeleteAll();
        int Count();
    }

　　json倉儲的具體實現：

    /// <summary>
    /// json倉儲
    /// </summary>
    public class JsonRepository<TEntity> :
        FileDatabase<TEntity>, IJsonRepository<TEntity>
        where TEntity : JsonEntity,new()
    {
        string m_Directory = AppDomain.CurrentDomain.BaseDirectory;

        public new bool IsIndent
        {
            get
            {
                return base.IsIndent;
            }

            set
            {
                base.IsIndent = value;
            }
        }

        public JsonRepository(string directory)
            :base(directory)
        {
            FileExtension = @"db";
            this.m_Directory = directory;
        }

        public JsonRepository()
        {
            FileExtension = @"db";
            MyDirectory = m_Directory;
        }

        public int Delete(TEntity item)
        {
            Delete(item.RootID);

            return 1;
        }

        public TEntity Find(params object[] id)
        {
            return FindOneById(id[0].ToString());
        }

        public IQueryable<TEntity> GetModel()
        {
            return FindAll().AsQueryable();
        }

        public int Insert(TEntity item)
        {
            Save(item.RootID, item);

            return 1;
        }

        public int Update(TEntity item)
        {
            Save(item.RootID, item);

            return 1;
        }

        protected override string Serialize(object value, bool isIndent = false)
        {
            return JsonHelper.Serialize(value, isIndent);
        }

        protected override TEntity Deserialize(string data)
        {
            return JsonHelper.Deserialize<TEntity>(data);
        }
    }

四、工具類

　　PublicHelper：

    /// <summary>
    ///     公共輔助操作類
    /// </summary>
    public static class PublicHelper
    {
        #region 公共方法

        /// <summary>
        /// Guid生成器
        /// </summary>
        /// <returns></returns>
        public static string GuidGenerator()
        {
            return Guid.NewGuid().ToString("N");
        }
        #endregion
    }

　　JsonHelper:

    public class JsonHelper
    {
        /// <summary>
        /// 序列化json
        /// </summary>
        /// <param name="value">對象</param>
        /// <param name="isIndented">是否縮進</param>
        /// <returns></returns>
        public static string Serialize(object value, bool isIndented)
        {
            if (value == null)
            {
                throw new ArgumentNullException("value is null.");
            }

            return JsonConvert.SerializeObject(value, isIndented ? Formatting.Indented : Formatting.None);
        }

        /// <summary>
        /// 將字符反序列化成對象
        /// </summary>
        /// <typeparam name="TEntity">泛型對象</typeparam>
        /// <param name="data"></param>
        /// <returns></returns>
        public static TEntity Deserialize<TEntity>(string data)
        {
            if (string.IsNullOrEmpty(data))
            {
                throw new ArgumentNullException("data is null or empty.");
            }

            return JsonConvert.DeserializeObject<TEntity>(data);
        }
    }

五、運行測試

　　測試代碼：

    class Program
    {
        static void Main(string[] args)
        {
            IJsonRepository<Student> jsonRepository = new JsonRepository<Student>();

            jsonRepository.Insert(new Student()
            {
                SNo = 1,
                Name = "張三",
                Gender = "女",
                Age = 18,
            });

            jsonRepository.Insert(new Student()
            {
                SNo = 2,
                Name = "李四",
                Gender = "女",
                Age = 18,
            });

            jsonRepository.Insert(new Student()
            {
                SNo = 3,
                Name = "王二",
                Gender = "女",
                Age = 18,
            });

            var entities = jsonRepository.GetModel();

            foreach (var item in entities)
            {
                Console.WriteLine(item.ToString());
            }

            Console.ReadKey();
        }
    }

    public class Student:JsonEntity
    {
        /// <summary>
        /// 學號
        /// </summary>
        public int SNo { get; set; }
        /// <summary>
        /// 名稱
        /// </summary>
        public string Name { get; set; }
        /// <summary>
        /// 性別
        /// </summary>
        public string Gender { get; set; }
        /// <summary>
        /// 年齡
        /// </summary>
        public int Age { get; set; }

        public override string ToString()
        {
            return string.Format("學號：{0};姓名：{1};性別：{2};年齡：{3}", this.SNo, this.Name, this.Gender, this.Age);
        }
    }

六、結語

　　整個本地文件系統數據就完成了，系統可以擴展為其它格式來進行數據存儲，只需要擴展倉儲就可以了，操作也是簡便，性能上的話，本地數據庫自然是比不上那些專用數據庫的，但是滿足日常肯定是沒有任何問題的。代碼比較完整，我就不上傳代碼了。

註：如有轉載請標註出處。

基於本地文件系統的LocalDB