LiteDB - FileStorage

December 19, 2017

為了控制記憶體的使用量，LiteDB 限制資料的存放量為 1 MB，1 MB 對於一般的資料而言是已經足夠了，但是對於二進制檔案來說就不怎麼足夠，所以 LiteDB 提供 FileStorage 用以存放二進制檔案。

FileStorage 支援以下方法：

Method	Description
Upload	Send file or stream to database. Can be used with file or Stream. If file already exists, file content is overwritten.
Download	Get your file from database and copy to Stream parameter
Delete	Delete a file reference and all data chunks
Find	Find one or many files in _files collection. Returns LiteFileInfo class, that can be download data after.
SetMetadata	pdate stored file metadata. This method doesn’t change the value of the stored file. It updates the value of _files.metadata.
OpenRead	Find file by _id and returns a LiteFileStream to read file content as stream

像是要塞入二進制的檔案，可以使用 FileStorage.Upload 方法，調用時帶入識別檔案用的 ID，以及檔案的位置。

…
using (var db = new LiteDatabase(dbFile)) 
{ 
  db.FileStorage.Upload(id, file); 
}

using System;
using System.IO;

namespace LiteDB.Demo4
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var db = new LiteDatabase("Person.db"))
            {
                var fs = db.FileStorage;
                var file = @"C:\Users\Public\Pictures\Sample Pictures\Chrysanthemum.jpg";
                var fileName = Path.GetFileName(file);
                fs.Upload(fileName, file);
            }
        }
    }
}

要開啟二進制檔案，可以使用 FileStorage.OpenRead 方法，調用時帶入識別檔案用的 ID。

…
using (var db = new LiteDatabase(dbFile)) 
{ 
  …  
  using (var stream = db.FileStorage.OpenRead(id)) 
  { 
    …
  } 
}

using System;
using System.IO;

namespace LiteDB.Demo4
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var db = new LiteDatabase("Person.db"))
            {
                var fs = db.FileStorage;
                var fileName = "Chrysanthemum.jpg";
                using(var fileStream = File.Create(fileName))
                using (var stream = fs.OpenRead(fileName))
                {
                    stream.CopyTo(fileStream);
                }
            }
        }
    }
}

要將 LiteDB 內的二進制檔案寫回硬碟，可以使用 FileStorage.Download 方法，調用時帶入識別檔案的 ID，及目的檔案串流。

…
using (var db = new LiteDatabase(dbFile)) 
{ 
  …  
  using(var fileStream = File.Create(id)) 
  { 
    fs.Download(id, fileStream); 
  } 
}

using System;
using System.IO;

namespace LiteDB.Demo5
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var db = new LiteDatabase("Person.db"))
            {
                var fs = db.FileStorage;
                var fileName = "Chrysanthemum.jpg";
                using (var fileStream = File.Create(fileName))
                {
                    fs.Download(fileName, fileStream);
                }
            }
        }
    }
}

LiteDB