The dialect class was not found

The dialect classes allow Hibernate to work with different types of databases. The problem was that Java was throwing a ClassNotFoundException because it could not find the new one. At first, we thought that the problem was that the class was on a different path or that the name was misspelled, but both were fine. The reason for the failure was that we had the database configuration written in a properties file to make it easier to change, and there was a blank space after the class name.

ORA-01882: timezone region not found

It was necessary to define the timezone. Initially, we changed this on Eclipse at Run configurations → Arguments → VM adding

-Duser.timezone="Europe/Madrid"

and then we changed it in Tomcat.

ORA-12514, TNS: listener does not currently know of service requested in connect descriptor

This means that the SID of the connection URL is incorrect, which is the word specified after the port.

ORA-00942: table or view does not exist

The message is very clear: a table was not created during the deployment. These are some of the possible causes:

• The name of a table is the same as the name of a system one, like SYS_USER
• The name of a column is one of the reserved keywords, like password or year

Hibernate does not throw an exception if it can not create a table during the deployment, so to find out why a create query has failed:

• Change the hibernate.show_sql property to true to show the generated queries
• Change the hibernate.hbm2ddl.auto property to create to force the creation of the tables
• Deploy again and look for the query creation statement related to the table that does not exist
• Execute it on a tool like Toad or SQL Developer

ORA-00928: missing SELECT keyword

A CRUD query contains the name of a column that is equal to a reserved keyword, so it can parse the query

ORA-01747: invalid user.table.column, table.column, or column specification

Another problem with column names is when they are equal to reserved keywords

Error defining boolean fields

We used to define boolean fields as this, so they could only have values 0 or 1:

@Column(name = C_COLUMN_NAME, columnDefinition = "BIT", nullable = false)
private Boolean fieldName;

However, Hibernate does not allow us to define columns as bits. So we changed the type to tiny int:

@Column(name = C_COLUMN_NAME, columnDefinition = "TINYINT(1)", nullable = false)
private Boolean fieldName;

Parameterized queries didn’t return the expected results

The application also reads from the database of a legacy application using prepared statements (without Hibernate), and we found that some of them were not returning results. The reason was that some text columns were not defined as varchar; you can find more information here.  

Fortunately, we had tests that alerted us about this error because it would have been difficult to detect it. As you can see, there may be many errors migrating a database, although Hibernate does a great job. I invite you to leave comments with other errors you had.