c# – 将数据流式传输到sql server数据库而不缓冲整个数据

我有一个Table Blob,它有一个varbinary(max)作为列.现在我想使用Filestream将数据存储到数据库中.数据可能非常大(在我的情况下为1.5GB),所以我不想将整个数据加载到缓冲区中.

我尝试了什么：

using (FileStream fs = File.Open(@"BigData.iso",FileMode.Open))
        {
            using (sqlConnection conn = new sqlConnection())
            {
                conn.ConnectionString = @"...";
                conn.open();
                sqlCommand command = new sqlCommand("INSERT INTO Blob Values (@0,@1)",conn);
                command.Parameters.Add(new sqlParameter("0",Guid.NewGuid()));
                var sqlb = new sqlBytes(fs);
                command.Parameters.Add(new sqlParameter("1",sqlDbType.VarBinary,-1)).Value = sqlb;
                command.ExecuteNonQuery();
            }
        }

但是我得到了一个OutOfMemoryException,因为sqlBytes将其缓冲区初始化为整个数据大小.

我知道微软有一个FILESTREAM功能,但我不想使用它.

有没有办法实现这个目标？

解决方法

您可以以小块的形式读取文件并将它们附加到数据列.

您将需要一个IDENTITY列或另一列,可用作执行UPDATE语句的键.以下是使用IDENTITY列的示例：

创建一个表来存储数据

CREATE TABLE [dbo].[table1](
    [ID] [int] IDENTITY(1,1) PRIMARY KEY NOT NULL,[Data] [varbinary](max) NULL,)

实现C#以块的形式插入/更新数据

private const string C_sqlConnectionString = @"Server=SERVERNAME;Database=dbnAME;Trusted_Connection=yes;";
private const int C_FileChunkSizeBytes = 1024 * 1024; // 1 MB

private static void storeFile(string filepath)
{
    using (FileStream fs = File.Open(filepath,FileMode.Open))
    {
        using (sqlConnection conn = new sqlConnection())
        {
            conn.ConnectionString = C_sqlConnectionString;
            conn.open();

            // Use a transaction to ensure that all parts of the file get stored to DB
            sqlCommand command = new sqlCommand("BEGIN TRAN",conn);
            command.ExecuteNonQuery();

            var pos = 0;
            byte[] fileBytes = null;
            int sqlRowId = 0;

            // Read the file in chunks
            while (pos < fs.Length)
            {
                // Read file bytes
                var bytesToRead = pos + C_FileChunkSizeBytes < fs.Length
                    ? C_FileChunkSizeBytes
                    : (int)(fs.Length - pos);

                fileBytes = new byte[bytesToRead];
                fs.Read(fileBytes,bytesToRead);

                // Store bytes to a parameter
                var varbinary = new sqlParameter("0",System.Data.sqlDbType.VarBinary,-1);
                varbinary.Value = fileBytes;

                if (pos == 0)
                {
                    // If this is the first chunk,then we need to INSERT
                    // The HOLDLOCK hint will hold a lock on the table until transaction completes (or is rolled back)
                    command = new sqlCommand("INSERT INTO [dbo].[table1] WITH(HOLDLOCK) VALUES(@0)",conn);
                    command.Parameters.Add(varbinary);
                    command.ExecuteNonQuery();

                    // Get the row ID for the inserted row
                    command = new sqlCommand("SELECT @@IDENTITY",conn);
                    sqlRowId = Convert.ToInt32(command.ExecuteScalar());
                }
                else
                {
                    // Update existing row and append data
                    command = new sqlCommand("UPDATE [dbo].[table1] SET [Data] = [Data] + @0 WHERE [ID] = @1",conn);
                    command.Parameters.Add(varbinary);
                    command.Parameters.Add(new sqlParameter("1",System.Data.sqlDbType.Int)).Value = sqlRowId;
                    command.ExecuteNonQuery();
                }

                // ** Good place for a breakpoint
                pos += bytesToRead;
            }

            // Commit transaction
            command = new sqlCommand("COMMIT TRAN",conn);
            command.ExecuteNonQuery();

            conn.Close();
        }
    }
}

测试

在while循环底部的C#代码中放置一个断点,例如pos = bytesToRead;.

在执行代码时,当代码执行在断点处停止时,检查sql中的数据：

SELECT *,LEN([Data]) AS [Length]
FROM [dbo].[table1] WITH(NOLOCK)

NOLOCK提示将让我们看到未提交的事务中的数据. LEN([Data])将显示每次迭代while循环后字段长度的增长情况.