Working with Hibernate and JPA I've had a problem generating a schema. The generation would fail with following message:
org.hibernate.tool.hbm2ddl.SchemaUpdate - main - BLOB/TEXT column 'field_id'
used in key specification without a key length
The JPA mapping causing the problem looked like following:
@Column(name = prefix + "field_id", length = 256, unique=true, nullable=false)
private String fieldId;
Apparently, using hibernate in combination with MySQL causes this failure. The key element on the mapping is the length attribute. I've had to change it to length=255 and everything worked again.
@Column(name = prefix + "field_id", length = 255, unique=true, nullable=false)
private String fieldId;
Give it a try!