Question

I am using the SQLite database and have the following persistent class (simplified):

public class Project {     public virtual int Id { get; set; }     public virtual DateTime StartDate { get; set; } } 

which is mapped to this table in the database:

CREATE TABLE projects (     id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,      start_date DATETIME ) 

Now I need to write a query that will select all the projects that have started in a given month.

In SQL I could use:

SELECT id FROM projects WHERE strftime('%m', start_date) = '12' 

What I dislike about this query is that it uses the database specific function ‘strftime‘.

So the following HQL is dependent on the underlying database:

// Get all projects that started in December (no matter which year) var projects = session     .CreateQuery(         'from Project p ' +         'where strftime('%m', p.StartDate) = :month')     .SetParameter('month', '12')     .List<Project>(); 

I have also tried ‘from Project p where p.StartDate.Month = 12’ but it didn’t work.

So using HQL or criteria API is it possible to write such a query in a database agnostic way?

Answer 1

If you’re regularly querying against months, days, years, you shouldn’t really be storing your date as a DateTime column – it makes the queries incredibly inefficient. You could easily create a ‘Month’ column and query against that (and your DBA would love you again)