Oracle database: How to read a BLOB?

Question

I\'m working with an Oracle database, and I would like to read the contents of a BLOB. How do I do this?

When I do a simple select statement, it merely returns \"(BLOB)

Answer 1

If you use the Oracle native data provider rather than the Microsoft driver then you can get at all field types

Dim cn As New Oracle.DataAccess.Client.OracleConnection
Dim cm As New Oracle.DataAccess.Client.OracleCommand
Dim dr As Oracle.DataAccess.Client.OracleDataReader

The connection string does not require a Provider value so you would use something like:

"Data Source=myOracle;UserID=Me;Password=secret"

Open the connection:

cn.ConnectionString = "Data Source=myOracle;UserID=Me;Password=secret"
cn.Open()

Attach the command and set the Sql statement

cm.Connection = cn
cm.CommandText = strCommand

Set the Fetch size. I use 4000 because it's as big as a varchar can be

cm.InitialLONGFetchSize = 4000

Start the reader and loop through the records/columns

dr = cm.ExecuteReader

Do while dr.read()
    strMyLongString = dr(i)
Loop

You can be more specific with the read, eg dr.GetOracleString(i) dr.GetOracleClob(i) etc. if you first identify the data type in the column. If you're reading a LONG datatype then the simple dr(i) or dr.GetOracleString(i) works fine. The key is to ensure that the InitialLONGFetchSize is big enough for the datatype. Note also that the native driver does not support CommandBehavior.SequentialAccess for the data reader but you don't need it and also, the LONG field does not even have to be the last field in the select statement.