71

私は sqlite を C++、Python で使用してきましたが、現在は (おそらく) C# で使用しています。これらすべてにおいて、ブロブをテーブルに挿入する方法がわかりません。sqliteでブロブを保存して取得するにはどうすればよいですか?

4

6 に答える 6

97

C＃でそれを行う方法は次のとおりです。

class Program
{
    static void Main(string[] args)
    {
        if (File.Exists("test.db3"))
        {
            File.Delete("test.db3");
        }
        using (var connection = new SQLiteConnection("Data Source=test.db3;Version=3"))
        using (var command = new SQLiteCommand("CREATE TABLE PHOTOS(ID INTEGER PRIMARY KEY AUTOINCREMENT, PHOTO BLOB)", connection))
        {
            connection.Open();
            command.ExecuteNonQuery();

            byte[] photo = new byte[] { 1, 2, 3, 4, 5 };

            command.CommandText = "INSERT INTO PHOTOS (PHOTO) VALUES (@photo)";
            command.Parameters.Add("@photo", DbType.Binary, 20).Value = photo;
            command.ExecuteNonQuery();

            command.CommandText = "SELECT PHOTO FROM PHOTOS WHERE ID = 1";
            using (var reader = command.ExecuteReader())
            {
                while (reader.Read())
                {
                    byte[] buffer = GetBytes(reader);
                }
            }

        }
    }

    static byte[] GetBytes(SQLiteDataReader reader)
    {
        const int CHUNK_SIZE = 2 * 1024;
        byte[] buffer = new byte[CHUNK_SIZE];
        long bytesRead;
        long fieldOffset = 0;
        using (MemoryStream stream = new MemoryStream())
        {
            while ((bytesRead = reader.GetBytes(0, fieldOffset, buffer, 0, buffer.Length)) > 0)
            {
                stream.Write(buffer, 0, (int)bytesRead);
                fieldOffset += bytesRead;
            }
            return stream.ToArray();
        }
    }
}
于 2009-03-09T09:01:05.123 に答える
9

私はblobを挿入するためのこのメソッドに行き着きました：

   protected Boolean updateByteArrayInTable(String table, String value, byte[] byteArray, String expr)
   {
      try
      {
         SQLiteCommand mycommand = new SQLiteCommand(connection);
         mycommand.CommandText = "update " + table + " set " + value + "=@image" + " where " + expr;
         SQLiteParameter parameter = new SQLiteParameter("@image", System.Data.DbType.Binary);
         parameter.Value = byteArray;
         mycommand.Parameters.Add(parameter);

         int rowsUpdated = mycommand.ExecuteNonQuery();
         return (rowsUpdated>0);
      }
      catch (Exception)
      {
         return false;
      }
   }

それを読み返すためのコードは次のとおりです。

   protected DataTable executeQuery(String command)
   {
      DataTable dt = new DataTable();
      try
      {
         SQLiteCommand mycommand = new SQLiteCommand(connection);
         mycommand.CommandText = command;
         SQLiteDataReader reader = mycommand.ExecuteReader();
         dt.Load(reader);
         reader.Close();
         return dt;
      }
      catch (Exception)
      {
         return null;
      }
   }

   protected DataTable getAllWhere(String table, String sort, String expr)
   {
      String cmd = "select * from " + table;
      if (sort != null)
         cmd += " order by " + sort;
      if (expr != null)
         cmd += " where " + expr;
      DataTable dt = executeQuery(cmd);
      return dt;
   }

   public DataRow getImage(long rowId) {
      String where = KEY_ROWID_IMAGE + " = " + Convert.ToString(rowId);
      DataTable dt = getAllWhere(DATABASE_TABLE_IMAGES, null, where);
      DataRow dr = null;
      if (dt.Rows.Count > 0) // should be just 1 row
         dr = dt.Rows[0];
      return dr;
   }

   public byte[] getImage(DataRow dr) {
      try
      {
         object image = dr[KEY_IMAGE];
         if (!Convert.IsDBNull(image))
            return (byte[])image;
         else
            return null;
      } catch(Exception) {
         return null;
      }
   }

   DataRow dri = getImage(rowId);
   byte[] image = getImage(dri);
于 2012-07-17T15:50:15.460 に答える
8

You need to use sqlite's prepared statements interface. Basically, the idea is that you prepare a statement with a placeholder for your blob, then use one of the bind calls to "bind" your data...

SQLite Prepared Statements

于 2009-03-09T06:22:31.557 に答える
3

In C++ (without error checking):

std::string blob = ...; // assume blob is in the string


std::string query = "INSERT INTO foo (blob_column) VALUES (?);";

sqlite3_stmt *stmt;
sqlite3_prepare_v2(db, query, query.size(), &stmt, nullptr);
sqlite3_bind_blob(stmt, 1, blob.data(), blob.size(), 
                  SQLITE_TRANSIENT);

That can be SQLITE_STATIC if the query will be executed before blob gets destructed.

于 2015-12-10T21:45:36.303 に答える