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如何从 sqlite 存储和检索 blob?

发布时间:  来源:互联网  作者:匿名  标签:blob error How do I store and retrieve a blob from sqlite? exception IT资讯 sqlite  热度:37.5℃

本文介绍了如何从 sqlite 存储和检索 blob?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

我在 C++、python 和现在(也许)在 C# 中使用过 sqlite.在所有这些中,我不知道如何将 blob 插入表中.如何在 sqlite 中存储和检索 blob?

I have used sqlite in c++, python and now (perhaps) in C#. In all of these I have no idea how to insert a blob into a table. How do I store and retrieve a blob in sqlite?

推荐答案

以下是您可以在 C# 中执行此操作的方法:

Here’s how you can do it in C#:

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();
        }
    }
}

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