检索与System.Data.SQLite和C＃中的BLOB [英] Retrieving a BLOB with System.Data.SQLite and C#
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问题描述
我是新手中的 SQLITE 的，我目前使用的 System.Data.SQLite.dll 版本 1.0.89.0 在< STRONG> C＃项目。 我的数据库包含了一个简单的表文件有下列：
I'm newbie in SQLITE and I'm currently using System.Data.SQLite.dll version 1.0.89.0 in a C# project. My database contains a simple table 'files' with following columns:
- [ID] VARCHAR（50）NOT NULL
- [块] INTEGER NOT NULL
- [内容] BLOB NOT NULL
- [大小] INTEGER NOT NULL
- [date_ins] DATETIME NOT NULL
- [id] VARCHAR(50) NOT NULL
- [chunk] INTEGER NOT NULL
- [content] BLOB NOT NULL
- [size] INTEGER NOT NULL
- [date_ins] DATETIME NOT NULL
PRIMARY KEY （ID，块）
我创建了一个类（ OfflineStorage ），在此表中添加和检索文件作为的 BLOBS 的。 保存方法效果不错，但加载生成一个 InvalidCastException的在 GetStream 扩展方法。
I created a class (OfflineStorage) to add and retrieve files in this table as BLOBS. Save method works ok, but Load generate an InvalidCastException on GetStream extended method.
public class OfflineStorage
{
private static string l_strConnectionTemplate = "Data Source={0};Version=3;Password=\"{1}\";";
private string l_strConnection;
private int SQLITE_MAX_BLOB_LENGTH;
private string l_strCreateTable = @"CREATE TABLE IF NOT EXISTS [files]" +
"( " +
" [id] VARCHAR(50) NOT NULL, " +
" [chunk] INTEGER NOT NULL, " +
" [content] BLOB NOT NULL, " +
" [size] INTEGER NOT NULL, " +
" [date_ins] DATETIME NOT NULL, " +
" PRIMARY KEY(id,chunk) " +
")";
private string l_strSelectQuery = @"SELECT chunk, content, size FROM files WHERE id = @id ORDER BY chunk";
private string l_strUpdateQuery = @"UPDATE files SET content = content || @new_content, size = size + @size WHERE id = @id AND chunk = @chunk";
private string l_strInsertQuery = @"INSERT INTO files(id, chunk, content, size, date_ins) VALUES(@id, @chunk, @new_content, @size, DATETIME('now'))";
public OfflineStorage(string strFilename, string strPassword = "")
{
SQLiteConnection l_objConnection = null;
if (!File.Exists(strFilename))
{
l_strConnection = string.Format(l_strConnectionTemplate, strFilename, "");
SQLiteConnection.CreateFile(strFilename);
l_objConnection = new SQLiteConnection(l_strConnection);
l_objConnection.SetPassword(strPassword);
l_objConnection.Close();
}
l_strConnection = string.Format(l_strConnectionTemplate, strFilename, strPassword);
l_objConnection = getConnection();
using (SQLiteCommand l_objCommand = new SQLiteCommand(l_strCreateTable, l_objConnection))
{
l_objCommand.ExecuteNonQuery();
}
SQLITE_MAX_BLOB_LENGTH = 1000000;
CloseConnection(l_objConnection);
}
private SQLiteConnection getConnection()
{
SQLiteConnection l_objConnection = null;
try
{
l_objConnection = new SQLiteConnection(l_strConnection);
l_objConnection.Open();
return l_objConnection;
}
catch (Exception ex)
{
CloseConnection(l_objConnection);
throw new OfflineStorageException("Local Service open db error.", ex);
}
}
private void CloseConnection(SQLiteConnection objConnection)
{
if (objConnection != null)
{
objConnection.Close();
objConnection = null;
}
}
public long Load(string strID, Stream objStream)
{
if (!objStream.CanWrite)
throw new NotSupportedException("Stream not writable.");
SQLiteConnection l_objConnection = getConnection();
// Columns Identifier (name of file)
SQLiteParameter l_objID = new SQLiteParameter("@id", DbType.String);
l_objID.Value = strID;
SQLiteCommand l_objCommand = new SQLiteCommand(l_strSelectQuery, l_objConnection);
l_objCommand.Parameters.Add(l_objID);
// Load File Records
SQLiteDataReader l_objReader;
try
{
l_objReader = l_objCommand.ExecuteReader();
}
catch (Exception ex)
{
CloseConnection(l_objConnection);
throw new OfflineStorageException("SQLite exception.", ex);
}
long l_lFileLength = 0; // Complete file length
int l_iDBChunk = -1; // Current chunk on database
int l_iChunk = 0; // Current 'sub chunk'
long l_lChunkLength = -1; // Current 'sub chunk' length
try
{
// For each record of current file selected by identifier
while (l_objReader.Read())
{
l_iDBChunk = l_objReader.GetInt32(0); // Chunk ID
l_lChunkLength = l_objReader.GetInt64(2); // Chunk size
Trace.Assert(l_iChunk == l_iDBChunk); // Compare expected Chunck with Database ID Chunk
l_lFileLength += l_objReader.GetStream(objStream, 1, l_lChunkLength); // Load chunk
l_iChunk++;
}
}
catch (Exception ex)
{
string l_strMessage = string.Format("SQLite exception on file {0}, DB chunk {1}: \n{2}", strID, l_iDBChunk, ex.Message);
throw new OfflineStorageException(l_strMessage, ex);
}
finally
{
l_objReader.Close();
l_objCommand.Dispose();
CloseConnection(l_objConnection);
}
if (l_iChunk < 1)
{
string l_strMessage = string.Format("File {0} not readed on db.", strID);
throw new OfflineStorageException(l_strMessage);
}
return l_lFileLength;
}
public void Save(string strID, Stream objStream, bool bOverwrite = false)
{
const int CHUNK_SIZE = 8 * 1024;
if (!objStream.CanRead)
throw new NotSupportedException("Stream not readable.");
long l_lOldPosition = objStream.Position;
SQLiteConnection l_objConnection = getConnection();
byte[] lar_byBuffer = new byte[CHUNK_SIZE];
SQLiteParameter l_objID = new SQLiteParameter("@id", DbType.String);
l_objID.Value = strID;
SQLiteParameter l_objContent = new SQLiteParameter("@new_content", DbType.Binary);
l_objContent.Value = lar_byBuffer;
SQLiteParameter l_objChunk = new SQLiteParameter("@chunk", DbType.Int32);
SQLiteParameter l_objSize = new SQLiteParameter("@size", DbType.Int32);
SQLiteCommand l_objCommand = new SQLiteCommand(l_strInsertQuery, l_objConnection);
l_objCommand.Parameters.Add(l_objID);
l_objCommand.Parameters.Add(l_objContent);
l_objCommand.Parameters.Add(l_objChunk);
l_objCommand.Parameters.Add(l_objSize);
int l_iReturn, l_lBytesRead;
int l_iChunk = 0; // Current 'sub chunk'
int l_iDBChunk = 0; // Current chunk on database
long l_lDBChunkLength = 0; // Current length of chunk
l_objChunk.Value = l_iDBChunk;
//Transaction
using (SQLiteTransaction l_objTransaction = l_objConnection.BeginTransaction())
{
// Read File from stream
while ((l_lBytesRead = objStream.Read(lar_byBuffer, 0, lar_byBuffer.Length)) > 0)
{
// Check for next Chunk
if ((l_lDBChunkLength + l_lBytesRead) >= SQLITE_MAX_BLOB_LENGTH)
{
l_objCommand.CommandText = l_strInsertQuery;
l_iChunk = 0; // reset 'sub chunk' counter
l_lDBChunkLength = 0; // reset chunk size
l_iDBChunk++; // increase chunk ID
l_objChunk.Value = l_iDBChunk;
}
l_lDBChunkLength += l_lBytesRead; // Increase length of chunk
l_objContent.Size = l_lBytesRead; // Length of Content field
l_objSize.Value = l_lBytesRead; // Chunk lenght (write on 'size' column)
#region WRITE
try
{
l_iReturn = l_objCommand.ExecuteNonQuery();
if (l_iChunk == 0)
{
l_objCommand.CommandText = l_strUpdateQuery;
}
}
catch (Exception ex)
{
l_objTransaction.Rollback();
CloseConnection(l_objConnection);
string l_strMessage = string.Format("SQLite exception on file {0}, DB chunk {1}, chunk {2}: \n{3}", strID, l_iDBChunk, l_iChunk, ex.Message);
throw new OfflineStorageException(l_strMessage, ex);
}
if (l_iReturn != 1)
{
l_objTransaction.Rollback();
CloseConnection(l_objConnection);
string l_strMessage = string.Format("DB chunk {1}, chunk {2} of file {0} not inserted on db.", strID, l_iDBChunk, l_iChunk);
throw new OfflineStorageException(l_strMessage);
}
#endregion WRITE
l_iChunk++;
}
l_objTransaction.Commit();
}
l_objCommand.Dispose();
CloseConnection(l_objConnection);
objStream.Position = l_lOldPosition;
}
}
DB数据读取器扩展类：
DB Data Reader Extended class:
public static class DbDataReaderExtension
{
public static long GetStream(this DbDataReader objReader, System.IO.Stream objStream, int iIndex = 0, long lFileLength = -1)
{
const int CHUNK_SIZE = 7 * 1024;
byte[] lar_byBuffer = new byte[CHUNK_SIZE]; // Buffer
long l_lBytesRead; // Bytes readed from SQLite database column
long l_lFieldOffset = 0; // Field offset on database column
long l_lBytesRemainig = lFileLength;
while ((l_lBytesRead = objReader.GetBytes(iIndex, l_lFieldOffset, lar_byBuffer, 0, lar_byBuffer.Length)) > 0)
{
l_lFieldOffset += l_lBytesRead; // prepare next offset
if (l_lBytesRemainig > 0) // check if a FileLength was set
{
l_lBytesRemainig -= l_lBytesRead; // remove readed bytes
if (l_lBytesRemainig < 0) // Cut last bytes not valid if file is bigger than column size
l_lBytesRead += l_lBytesRemainig;
}
// write only valid bytes
objStream.Write(lar_byBuffer, 0, (int)l_lBytesRead);
}
return lFileLength < 0 ? l_lFieldOffset : lFileLength;
}
}
我发现，产生这种异常，因为的ReadBytes方法（SQLiteDataReader）调用VerifyType
I found this exception is generated because ReadBytes method (SQLiteDataReader) call VerifyType
private TypeAffinity VerifyType(int i, DbType typ)
{
CheckClosed();
CheckValidRow();
TypeAffinity affinity = GetSQLiteType(i).Affinity;
switch (affinity)
{
...
case TypeAffinity.Text:
if (typ == DbType.SByte) return affinity;
if (typ == DbType.String) return affinity;
if (typ == DbType.SByte) return affinity;
if (typ == DbType.Guid) return affinity;
if (typ == DbType.DateTime) return affinity;
if (typ == DbType.Decimal) return affinity;
break;
case TypeAffinity.Blob:
...
}
throw new InvalidCastException();
}
在此功能是没有预料到的典型值等于为的 DbType.Binary 的和亲和力的等于 TypeAffinity.Text 的。
谁能帮我理解这个问题？
谢谢
In this function isn't expected that typ is equal to DbType.Binary and affinity is equal to TypeAffinity.Text.
Can anyone help me to understand this problem?
Thank you
推荐答案
确定，这里就是我已经添加和检索斑点。
ok, here's how i have added and retrieved blobs.
我想这一切都取决于byte []的是否是可管理的大小。这个工作对小物体被序列化到数据库中。
i suppose it all depends on whether the byte[] is a manageable size. This worked for small objects being serialized to the database.
使用GetDataTable来获取数据，然后有问题的行提取的字节数组以下内容：
use GetDataTable to get the data and then on the row in question extract the byte array with the following:
public byte[] getByteArray(DataRow row, int offset)
{
object blob = row[offset];
if (blob == null) return null;
byte[] arData = (byte[])blob;
return arData;
}
这是我如何添加它们：
private System.Object syncLock = new System.Object();
public int ExecuteNonQueryWithBlob(string sql, string blobFieldName, byte[] blob)
{
lock (syncLock)
{
try
{
using (var c = new SQLiteConnection(dbConnection))
{
using (var cmd = new SQLiteCommand(sql, c))
{
cmd.Connection.Open();
cmd.Parameters.AddWithValue("@" + blobFieldName, blob);
return cmd.ExecuteNonQuery();
}
}
}
catch (Exception e)
{
Console.WriteLine(e.Message);
return 0;
}
}
}
public DataTable GetDataTable(string sql)
{
lock (syncLock)
{
try
{
DataTable dt = new DataTable();
using (var c = new SQLiteConnection(dbConnection))
{
c.Open();
using (SQLiteCommand cmd = new SQLiteCommand(sql, c))
{
using (SQLiteDataReader rdr = cmd.ExecuteReader())
{
dt.Load(rdr);
return dt;
}
}
}
}
catch (Exception e)
{
Console.WriteLine(e.Message);
return null;
}
}
}
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