Consider this Hibernate mapping

@Column(name = "qReferenceId")
public Long getQReferenceId() {
return qReferenceId;
}

Where qReferenceId is data provided to our application via a external reference, we do not have a QReference Object or Table for FK references.When trying to query this object using DetachedQuery, this Simple expression was used.

public List findByQReferenceId(Long id) {
     final SimpleExpression matchesId = Property.forName("qReferenceId").eq(id);
    DetachedCriteria criteria = DetachedCriteria.forClass(Movie.class);
    criteria = criteria.add(matchesId);
    List movies = (List) getHibernateTemplate().findByCriteria(criteria);
    return movies;
}

When running this method, I kept getting errors shown below.

could not resolve property: qReferenceId of: com.example.Movie; 

nested exception is org.hibernate.QueryException: could not resolve property: qReferenceId of: com.example.Movie

....

....

I thought I had a spelling mistake on the property name and also tried many other combinations. Finally I said why not use "QReferenceId" and suddenly everything was hunky dory, this kind of weirdness does not happen when working with property names that do not have consecutive double uppercase characters in the getter/setter for the property. very interesting. So this method worked

public List findByQReferenceId(Long id) {
    final SimpleExpression matchesId = Property.forName("QReferenceId").eq(id);
    DetachedCriteria criteria = DetachedCriteria.forClass(Movie.class);
    criteria = criteria.add(matchesId);
    List movies = (List) getHibernateTemplate().findByCriteria(criteria);
    return movies;
}

Recently when our test databases where upgraded new version of Oracle, we started noticing that the order in which some drop down lists were being displayed was not correct. It turns out that the SELECT statement we had, did not have a ORDER BY clause and the data was being returned in the ORDER of the creation of rows (in the order of ROWID) when the database was upgraded these ROWID's got changed and hence the ORDER of the data being shown in the drop down lists.

Lesson learnt: have a EXPLICIT ORDER BY in every SQL that provides data to be shown on the screen. In other words do not rely on the order of the result set provided by the current version of the database server. if you prefer a certain order make that choice explicit in the SQL SELECT statement.

Couple of weeks back I was given a choice to upgrade my work Laptop to a Mac Book Pro or a Windows Laptop. I choose Mac ( I know everyone is into macs nowadays). The transition was pretty good, with the exception of moving my oracle database from windows to mac, since there is no native installation of oracle on mac I had to use VMWare fusion to install oracle.

After having oracle run inside the VM, I started setting up the dev environment, I ran into issues with ANT version and JAVA version but they where resolved by pointing to the right location.

Overall this has been a positive experience so far.

When creating a Foreign Key constraint on the database as shown below

ALTER TABLE BOOK ADD 
    (CONSTRAINT FK_BOOK_AUTHOR FOREIGN KEY (AUTHORID) 
     REFERENCES AUTHOR)
/

In the above example we are telling the database to check if the BOOK.AUTHORID is a valid value in the Author.AuthorID. When the Author table is being changed, the database does data verification on the BOOK table using SELECT against the BOOK table for the AUTHORID some thing like this

SELECT count(*) FROM BOOK WHERE AUTHORID = nnnn

Basically the database server is trying to check if it has children rows for the row that just changed (inserted or deleted). While doing this if there is not index on BOOK.AUTHORID, the database will have to scan the whole table which is slow. Hence when creating a Foreign Key constraint, remember to create a corresponding INDEX on the table, so that the performance does not degrade, or when observing slow performance on a database after you put in Foreign Key constraints. Make sure to look for Indexes on the columns that are constrained.

So we version control/source control everything on our project.. code/data/artifacts/diagrams etc. yesterday I said why not extend it to my writings to everything I have. So I started this long journey of refactoring my folder layout and making a nice folder structure to hold all the things I have written about have other artifacts in the process of writing and moved them all to subversion, now all my example code and writings are all under version control that gets backed up everyday.... feels liberating