BLOB/TEXT column 'description' used in key specification without a key length

This post is not about solving some problem. Sadly I don't know hot to solve following problem. There are just work arounds. I have following configuration:

MySQL: 5.5.27
hibernate dialect: org.hibernate.dialect.MySQLInnoDBDialect
hibernate: 3.6.9

In my model I have entity with following attribute:

@Entity
@Table(name = "site")
public class Site extends AbstractEntity {
    
    ...
     
    @Column(unique = true, nullable = true, length = 1024 * 100)
    private String description;
    
    ...
     
}

When I run program follow error appears in logs and table site is not created.

2013-06-01 12:15:24 [main] ERROR org.hibernate.tool.hbm2ddl.SchemaUpdate - 
Unsuccessful: create table site (id_site integer not null auto_increment, description longtext unique, name varchar(250) unique, url_pattern longtext not null unique, id_image integer, primary key (id_site)) ENGINE=InnoDB
2013-06-01 12:15:24 [main] ERROR org.hibernate.tool.hbm2ddl.SchemaUpdate - 
BLOB/TEXT column 'description' used in key specification without a key length

Problem is that column 'description' is marked as unique. In InnoDB maximum length of key could be just 767 characters for a single-byte charset like LATIN1 and only 255 characters for UTF8. Look at possible workarounds:

1. avoid indexes, don't use unique = true
2. make column length smaller (255) characters for UTF8
3. compute hash from long column store in in another column and create index on hash column

If you'll have some other possible solution than please let me know.

Useful MySQL commands

This is not MySQL tutorial. It's just list of useful SQL statements that I don't remember and I don't want to google them anymore. SQL commanda are also in basic form. For more detail see original MySQL documentation.

Create new user with login name 'userName' with password 'passwd'. Created use have access to all tables in database 'testDb'.

GRANT ALL PRIVILEGES ON testDb.* TO 'userName'@'host' IDENTIFIED BY 'passwd';

Create new database with default text columns encoding.

CREATE SCHEMA `testDb` DEFAULT CHARACTER SET utf8 ;

Set password for user 'sa' accessing from localhost to 'be'.

SET PASSWORD FOR sa@localhost = PASSWORD('be');

Create SQL file containing all data form database. It's useful for creating backups and for copying data from one db into another one.

mysqldump --add-drop-table -u sa -psa bl > bl.sql