oracle 尝试读取 blob
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Trying to read a blob
提问by Kasper Hansen
I am trying to read a BLOB from an Oracle database. The function GetFileContent take p_file_id as a paramater and return a BLOB. The BLOB is a DOCX-file that needs to be written in a folder somewhere. But I can't quite figure out how to read the BLOB. There is definitely something stored in the return_value-paramater after
我正在尝试从 Oracle 数据库中读取 BLOB。函数 GetFileContent 以 p_file_id 作为参数并返回一个 BLOB。BLOB 是一个 DOCX 文件，需要写入某个文件夹中。但我不太清楚如何读取 BLOB。肯定有东西存储在 return_value-paramater 之后
OracleDataReader reader = cmd.ExecuteReader(CommandBehavior.SequentialAccess);
The value is {byte[9946]}. But I get an error when executing
值为 {byte[9946]}。但是我在执行时出错
long retrievedBytes = reader.GetBytes(1, startIndex, buffer, 0, ChunkSize);
It says InvalidOperationException was caught: "No data exists for the row or column."
它说 InvalidOperationException 被捕获：“行或列不存在数据。”
Here is the code:
这是代码：
cmd = new OracleCommand("GetFileContent", oraCon);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("p_file_id", OracleType.Number).Direction = ParameterDirection.Input;
cmd.Parameters[0].Value = fileID;
cmd.Parameters.Add("return_value", OracleType.Blob).Direction = ParameterDirection.ReturnValue;
cmd.Connection.Open();
OracleDataReader reader = cmd.ExecuteReader(CommandBehavior.SequentialAccess);
reader.Read();
MemoryStream memory = new MemoryStream();
long startIndex = 0;
const int ChunkSize = 256;
while (true)
{
byte[] buffer = new byte[ChunkSize];
long retrievedBytes = reader.GetBytes(1, startIndex, buffer, 0, ChunkSize); //FAILS
memory.Write(buffer, 0, (int)retrievedBytes);
startIndex += retrievedBytes;
if (retrievedBytes != ChunkSize)
break;
}
cmd.Connection.Close();
byte[] data = memory.ToArray();
memory.Dispose();
How can I read the BLOB from the function?
如何从函数中读取 BLOB？
采纳答案by Mike Ohlsen
Looks like you are using the Microsoft Oracle Client. You probably want to use the LOB objects rather than using GetBytes(...).
看起来您正在使用 Microsoft Oracle Client。您可能想要使用 LOB 对象而不是使用 GetBytes(...)。
I think the first link below would be the easiest for you. Here is an excerpt:
我认为下面的第一个链接对您来说是最简单的。这是摘录：
using(reader)
{
//Obtain the first row of data.
reader.Read();
//Obtain the LOBs (all 3 varieties).
OracleLob BLOB = reader.GetOracleLob(1);
...
//Example - Reading binary data (in chunks).
byte[] buffer = new byte[100];
while((actual = BLOB.Read(buffer, 0, buffer.Length)) >0)
Console.WriteLine(BLOB.LobType + ".Read(" + buffer + ", " + buffer.Length + ") => " + actual);
...
}
OracleDataReader::GetOracleLob Method
OracleDataReader::GetOracleLob 方法
On a side note, the Microsoft Oracle client is being depreciated. You may want look into switching to Oracle's ODP.net, as that will be the only "Officially Supported" client moving forward.
附带说明一下，Microsoft Oracle 客户端正在贬值。您可能需要考虑切换到 Oracle 的 ODP.net，因为这将是唯一向前发展的“官方支持”客户端。
