Toplink with mysql: problem with blob size

Question

I'm using toplink with a mysql database. I want to store some data in a blob.
In mysql there exist different sizes of blobs (in my case I need a mediumblob).
But if I create the scheme for the database with jpa/toplink it alway creates only a column with type blob.
I can explicitly tell the database to use a mediumblob by this:
@Column("MEDIUMBLOB")
But by doing this I limit my program to mysql of course, as this data type is not known to other databases.
Does anybody know a more elegant solution to setting the blob size?
for example with hibernate it can be done this way:
@Column(length=666666)

Answer 1

Looks like you are using JPA, and in JPA you would set the columnDefinition to the type that you want, e.g.
@Lob
@Column(name="BLOBCOL", columnDefinition="MEDIUMBLOB")
byte[] myByteData;
As you mentioned, this does introduce a dependency on the database. However, you can always either put the Column metadata in XML, or override it with something else later in XML.
The length attribute was intended and specified for use with Strings but I guess there is no reason why it couldn't be used for BLOBs as well (please enter an enhancement request, or submit the code to add the feature to EclipseLink). Be aware, though, that doing so at this stage is going to be introducing a dependency on the provider to support a non-spec defined feature.