MATLAB: Does an array of doubles stored as blobs in a Database table truncated to 8-bit integers when fetched using Database Toolbox

Question

I am storing an array of doubles into a database table as blobs. However when I read them back in, I see they are truncated to 8-bit integers.

Answer 1

The blob datatype is treated as binary strings (byte strings). The JDBC interface defines methods for blobs that operate on byte arrays. As the Database Toolbox uses JDBC or JDBC-ODBC bridge, the data passed from the MATLAB end is converted to a JAVA byte array. In the case of a array of doubles, it is truncated while being converted to an array of bytes. Thus the fetch command returns uint8.

As a workaround, convert the double values to their byte representation using the TYPECAST function. For example if "x" is a array of doubles, the following command:

y=typecast(x,'int8');

will convert it to a array of int8. Now "y" can be inserted into the blob column.

A post processing step will be needed after fetching the data. For example to convert "y" into a array of double, the command is:

x = typecast(y,'double');