Stop Unit Testing Database Code

Writing tests that use an actual database is hard.


Now that this has been established, let’s have a look at a blog post by Marco Behler, in which he elaborates on various options when testing database code, with respect to transactionality. Testing database transactions is even harder than just testing database code. Marco lists a couple of options how to tweak these tests to make them “easier” to write.

One of the options is:

3. Set the flush-mode to FlushMode.ALWAYS for your tests

(note, this is about testing Hibernate code).

Marco puts this option in parentheses, because he’s not 100% convinced if it’s a good idea to test different behaviour from the productive one. Here’s our take on that:

Stop Unit Testing Database Code

By the time you start thinking about tweaking your test setup to achieve “simpler” transaction behaviour (or worse, use mocks for your database), you’re pretty much doomed. You start creating an alternative system that heavily deviates from your productive system. This essentially means:

  • that results from tests against your test system have (almost) no meaning
  • that your tests will not cover some of the most complex aspects of your productive system
  • that you will start spending way too much time on tweaking tests rather than implementing useful business logic

Instead, focus on writing integration tests that test your business logic on a very high level, i.e. on a “service layer” level, if your architecture has such a thing. If you’re using EJB, this would probably be on a session bean level. If you’re using REST or SOAP, this would be on a REST or SOAP service level. If you’re using HTTP (the retro name for REST), it would be on an HTTP service level.

Here are the advantages of this approach:

  • You might not get 100% coverage, but you will get the 80% coverage for those parts that really matter (with 20% of the effort). Your UI (or external system) doesn’t call the database in the quirkiest of forms either. It calls your services. Why would you test anything other than your services?
  • Your tests are very easy to maintain. You have a public API to your UI (or external system). It’s formal and easy to understand. It’s a black box with well-defined input and output parameters, which makes it easy to read / write tests

Databases are stateful. Obviously

What you have to do is let go of this idea that your database will ever participate in a “unit” (as in “unit” test). Units are pretty stateless, and thus it is very easy to write mutually independent unit tests for functional algorithms, for instance.

Databases couldn’t be any less stateless. The whole idea of a database is to manage state. And that’s very complicated and completely opposite to what any unit test can ever model. Many of the most meaningful state transitions span several database interactions, or even transactions, or maybe even services. For instance, it may be important that the CREATE_USER service invocation be immediately followed by an invocation of CHANGE_PASSWORD. You can only integration-test that on a service layer. Don’t believe it? What if CREATE_USER depends on an external LDAP system? Or complex security logic in stored procedures? Your integration test’s got that covered.


Writing tests that use an actual database is hard.

Yes. That won’t change. But your perception may. Don’t try to tweak things around this fact. Create a well-known test database. Reset it between tests. And write integration tests on a very high level. The 20/80 cost/benefit ratio will leave you no better choice.

Stay tuned for another blog post on this blog about how we integration-test the jOOQ API against 16 actual RDBMS

Flyway and jOOQ for Unbeatable SQL Development Productivity

When performing database migrations, we at Data Geekery recommend using jOOQ with Flyway – Database Migrations Made Easy. In this post, we’re going to look into a simple way to get started with the two frameworks.


There are a variety of ways how jOOQ and Flyway could interact with each other in various development setups. In this tutorial we’re going to show just one variant of such framework team play – a variant that we find particularly compelling for most use cases.

The general philosophy and workflow behind the following approach can be summarised as this:

  • 1. Database increment
  • 2. Database migration
  • 3. Code re-generation
  • 4. Development

The four steps above can be repeated time and again, every time you need to modify something in your database. More concretely, let’s consider:

  • 1. Database increment – You need a new column in your database, so you write the necessary DDL in a Flyway script
  • 2. Database migration – This Flyway script is now part of your deliverable, which you can share with all developers who can migrate their databases with it, the next time they check out your change
  • 3. Code re-generation – Once the database is migrated, you regenerate all jOOQ artefacts (see code generation), locally
  • 4. Development – You continue developing your business logic, writing code against the udpated, generated database schema

0.1. Maven Project Configuration – Properties

The following properties are defined in our pom.xml, to be able to reuse them between plugin configurations:


0.2. Maven Project Configuration – Dependencies

While jOOQ and Flyway could be used in standalone migration scripts, in this tutorial, we’ll be using Maven for the standard project setup. You will also find the source code of this tutorial on GitHub, and the full pom.xml file here.

These are the dependencies that we’re using in our Maven configuration:

<!-- We'll add the latest version of jOOQ 
     and our JDBC driver - in this case H2 -->

<!-- For improved logging, we'll be using 
     log4j via slf4j to see what's going
     on during migration and code generation -->

<!-- To esnure our code is working, we're
     using JUnit -->

0.3. Maven Project Configuration – Plugins

After the dependencies, let’s simply add the Flyway and jOOQ Maven plugins like so. The Flyway plugin:


    <!-- Note that we're executing the Flyway
         plugin in the "generate-sources" phase -->

    <!-- Note that we need to prefix the db/migration
         path with filesystem: to prevent Flyway
         from looking for our migration scripts
         only on the classpath -->

The above Flyway Maven plugin configuration will read and execute all database migration scripts from src/main/resources/db/migrationprior to compiling Java source code. While the official Flyway documentation suggests that migrations be done in the compile phase, the jOOQ code generator relies on such migrations having been done prior to code generation.

After the Flyway plugin, we’ll add the jOOQ Maven Plugin. For more details, please refer to the manual’s section about the code generation configuration.


    <!-- The jOOQ code generation plugin is also 
         executed in the generate-sources phase,
         prior to compilation -->

    <!-- This is a minimal working configuration. 
         See the manual's section about the code
         generator for more details -->

This configuration will now read the FLYWAY_TEST schema and reverse-engineer it into the target/generated-sources/jooq-h2 directory, and within that, into the org.jooq.example.flyway.db.h2 package.

1. Database increments

Now, when we start developing our database. For that, we’ll create database increment scripts, which we put into thesrc/main/resources/db/migration directory, as previously configured for the Flyway plugin. We’ll add these files:

  • V1__initialise_database.sql
  • V2__create_author_table.sql
  • V3__create_book_table_and_records.sql

These three scripts model our schema versions 1-3 (note the capital V!). Here are the scripts’ contents

-- V1__initialise_database.sql

CREATE SCHEMA flyway_test;
-- V2__create_author_table.sql
CREATE SEQUENCE flyway_test.s_author_id START WITH 1;

  first_name VARCHAR(50),
  last_name VARCHAR(50) NOT NULL,
  date_of_birth DATE,
  year_of_birth INT,
  address VARCHAR(50),

-- V3__create_book_table_and_records.sql
  author_id INT NOT NULL,
  title VARCHAR(400) NOT NULL,

  CONSTRAINT pk_t_book PRIMARY KEY (id),
  CONSTRAINT fk_t_book_author_id FOREIGN KEY (author_id) REFERENCES

INSERT INTO VALUES (next value for flyway_test.s_author_id, 'George', 'Orwell', '1903-06-25', 1903, null);
INSERT INTO VALUES (next value for flyway_test.s_author_id, 'Paulo', 'Coelho', '1947-08-24', 1947, null);

INSERT INTO VALUES (1, 1, '1984');
INSERT INTO VALUES (2, 1, 'Animal Farm');
INSERT INTO VALUES (3, 2, 'O Alquimista');
INSERT INTO VALUES (4, 2, 'Brida');

2. Database migration and 3. Code regeneration

The above three scripts are picked up by Flyway and executed in the order of the versions. This can be seen very simply by executing:

mvn clean install

And then observing the log output from Flyway…

[INFO] --- flyway-maven-plugin:3.0:migrate (default) @ jooq-flyway-example ---
[INFO] Database: jdbc:h2:~/flyway-test (H2 1.4)
[INFO] Validated 3 migrations (execution time 00:00.004s)
[INFO] Creating Metadata table: "PUBLIC"."schema_version"
[INFO] Current version of schema "PUBLIC": <>
[INFO] Migrating schema "PUBLIC" to version 1
[INFO] Migrating schema "PUBLIC" to version 2
[INFO] Migrating schema "PUBLIC" to version 3
[INFO] Successfully applied 3 migrations to schema "PUBLIC" (execution time 00:00.073s).

… and from jOOQ on the console:

[INFO] --- jooq-codegen-maven:3.5.0-SNAPSHOT:generate (default) @ jooq-flyway-example ---
[INFO] Using this configuration:
[INFO] Generating schemata      : Total: 1
[INFO] Generating schema        :
[INFO] ----------------------------------------------------------
[INFO] GENERATION FINISHED!     : Total: 337.576ms, +4.299ms

4. Development

Note that all of the previous steps are executed automatically, every time someone adds new migration scripts to the Maven module. For instance, a team member might have committed a new migration script, you check it out, rebuild and get the latest jOOQ-generated sources for your own development or integration-test database.

Now, that these steps are done, you can proceed writing your database queries. Imagine the following test case

import org.jooq.Result;
import org.jooq.impl.DSL;
import org.junit.Test;

import java.sql.DriverManager;

import static java.util.Arrays.asList;
import static org.jooq.example.flyway.db.h2.Tables.*;
import static org.junit.Assert.assertEquals;

public class AfterMigrationTest {

    public void testQueryingAfterMigration() throws Exception {
        try (Connection c = DriverManager.getConnection("jdbc:h2:~/flyway-test", "sa", "")) {
            Result<?> result =

            assertEquals(4, result.size());
            assertEquals(asList(1, 2, 3, 4), result.getValues(BOOK.ID));

If you run the mvn clean install again, the above integration test will now compile and pass!


The power of this approach becomes clear once you start performing database modifications this way. Let’s assume that the French guy on our team prefers to have things his way (no offense intended ;-) ):

-- V4__le_french.sql
  ALTER COLUMN title RENAME TO le_titre;

They check it in, you check out the new database migration script, run

mvn clean install

And then observe the log output:

[INFO] --- flyway-maven-plugin:3.0:migrate (default) @ jooq-flyway-example ---
[INFO] --- flyway-maven-plugin:3.0:migrate (default) @ jooq-flyway-example ---
[INFO] Database: jdbc:h2:~/flyway-test (H2 1.4)
[INFO] Validated 4 migrations (execution time 00:00.005s)
[INFO] Current version of schema "PUBLIC": 3
[INFO] Migrating schema "PUBLIC" to version 4
[INFO] Successfully applied 1 migration to schema "PUBLIC" (execution time 00:00.016s).

So far so good, but later on:

[INFO] -------------------------------------------------------------
[ERROR] C:\...\[24,19] error: cannot find symbol
[INFO] 1 error

When we go back to our Java integration test, we can immediately see that the TITLE column is still being referenced, but it no longer exists:

public class AfterMigrationTest {

    public void testQueryingAfterMigration() throws Exception {
        try (Connection c = DriverManager.getConnection("jdbc:h2:~/flyway-test", "sa", "")) {
            Result<?> result =
                   //   ^^^^^ This column no longer exists. 
                   //   We'll have to rename it to LE_TITRE

            assertEquals(4, result.size());
            assertEquals(asList(1, 2, 3, 4), result.getValues(BOOK.ID));


This tutorial shows very easily how you can build a rock-solid development process using Flyway and jOOQ to prevent SQL-related errors very early in your development lifecycle – immediately at compile time, rather than in production!

Visit the Flyway website and the jOOQ website.

Should I Put That Table Alias or Not?

Infrequent SQL developers often get confused about when to put parentheses and/or aliases on derived tables. There has been this recent Reddit discussion about the subject, where user Elmhurstlol was wondering why they needed to provide an alias to the derived table (the subselect with the UNION) in the following query:

  SELECT price from product a JOIN pc b
  ON a.model=b.model AND maker='A'
  SELECT price from product a JOIN laptop c
  ON a.model=c.model and maker='A'
) hello

The question really was about why the "hello" table alias was necessary, because often it seems not to be required.

Here’s what the SQL standard states

If in doubt, it is often useful to consider the SQL standard about the rationale behind some syntax elements. In this case, let’s consider the freely available SQL 1992 standard text (for simplicity), and see how it specifies table references:

<table reference> ::=
    <table name> [ [ AS ] <correlation name>
        [ <left paren> <derived column list> 
          <right paren> ] ]
  | <derived table> [ AS ] <correlation name>
        [ <left paren> <derived column list>
          <right paren> ]
  | <joined table>

<derived table> ::= <table subquery>

<table subquery> ::= <subquery>

<subquery> ::= <left paren> <query expression>
               <right paren>

(for more information about the awesome and completely underused derived column list feature, read this article here)

The essence of the above syntax specification is this:

  • A derived table MUST always be aliased
  • The AS keyword is optional, for improved readability
  • The parentheses MUST always be put around subqueries

Following these rules, you’ll be pretty safe in most SQL dialects. Here are some deviations to the above, though:

  • Some dialects allow for unaliased derived tables. However, this is still a bad idea, because you will not be able to unambiguously qualify a column from such a derived table


Always provide a meaningful alias to your derived tables. As simple as that.


Most databases that support default values on their column DDL, it is also possible to actually alter that default. An Oracle example:


-- Oops, wrong default, let us change it

-- Now that is better

Unfortunately, this isn’t possible in SQL Server, where the DEFAULT column property is really a constraint, and probably a constraint whose name you don’t know because it was system generated.

But luckily, jOOQ 3.4 now supports DDL and can abstract this information away from you by generating the following Transact-SQL program:

DECLARE @constraint NVARCHAR(max);
DECLARE @command NVARCHAR(max);

SELECT @constraint = name
FROM sys.default_constraints
WHERE parent_object_id = object_id('t')
AND parent_column_id = columnproperty(
    object_id('t'), 'val', 'ColumnId');

IF @constraint IS NOT NULL
    + @constraint;
  EXECUTE sp_executeSQL @command

    + @constraint + ' DEFAULT -1 FOR val';
  EXECUTE sp_executeSQL @command
  SET @command = 'ALTER TABLE t ADD DEFAULT -1 FOR val';
  EXECUTE sp_executeSQL @command

This program will either drop and create a new constraint with the same name, or create an entirely new constraint with a system-generated name.

With jOOQ, you can execute this statement as such:


What Big Data Really Is

One for the weekend: Big Data

Java 8 Friday: The Best Java 8 Resources – Your Weekend is Booked

At Data Geekery, we love Java. And as we’re really into jOOQ’s fluent API and query DSL, we’re absolutely thrilled about what Java 8 will bring to our ecosystem.

Every Friday, we’re showing you a couple of nice new tutorial-style Java 8 features, which take advantage of lambda expressions, method references, default methods, the Streams API, and other great stuff. You’ll find the source code on GitHub.

The Best Java 8 Resources – Your Weekend is Booked

We’re obviously not the only ones writing about Java 8. Ever since this great language update’s go live, there had been blogs all around the world appearing with great content and different perspectives on the subject. In this edition of the Java 8 Friday series, we’d like to summarise some of the best content that has been going on on that subject.

1. Brian Goetz’s Answers on Stack Overflow

Brian Goetz was the spec lead for JSR 335. Together with his Expert Group team, he has worked very hard to help Java 8 succeed. However, now that JSR 335 has shipped, his work is far from being over. Brian has had the courtesy of giving authoritative answers to questions from the Java community on Stack Overflow. Here are some of the most interesting questions:

Thumbs up to this great community effort. It cannot get any better than hearing authoritative answers from the spec lead himself.

2.’s Collection of Java 8 Resources

This list of resources wouldn’t be complete without the very useful list of Java 8 resources (mostly authoritative links to specifications) from the guys over at Here is:

3. The jOOQ Blog’s Java 8 Friday Series

Yay, that’s us! :-)

Yes, we’ve worked hard to bring you the latest from our experience when integrating jOOQ with Java 8. Here are some of our most popular articles from the recent months:

4. ZeroTurnaround’s RebelLabs Blog

As part of the ZeroTurnaround content marketing strategy, ZeroTurnaround has launched RebelLabs quite a while ago where various writers publish interesting articles around the topic of Java, which aren’t necessarily related to JRebel and other ZT products. There is some great Java 8 related content having been published over there. Here are our favourite gems:

5. The Takipi Blog

Just like ZeroTurnaround and ourselves, our friends over at Takipi provide you with some awesome Java 8 content on their blog.

6. Benji Weber’s Fun Experiments with Java 8

This blog series we found particularly fun to read. Benji Weber really thinks outside of the box and does some crazy things with default methods, method references and all that. Things that Java developers could only dream of, so far. Here are:

7. The Geeks from Paradise Blog’s Java 8 Musings

Edwin Dalorzo from Informatech has been treating us with a variety of well-founded comparisons between Java 8 and .NET. This is particularly interesting when comparing Streams with LINQ. Here are some of his best writings:

Is this list complete?

No, it is missing many other, very interesting blog series. Do you have a series to share? We’re more than happy to update this post, just let us know (in the comments section)

Scala Code Trollin’

So, we’ve all heard of “flatmap that sh**”, right? The new, functional, hipster way of saying

You’re doing it wrong

Since we don’t really care about dogma and functional religion that much, let’s just start trolling a little (it’s so much easier anyway), with Scala code. Check out the following piece of useful Scala code, which does compile:

def C = Seq(1, 2, 3)
def Windows = 0
def WAT = (C:\Windows)                                                           /* OK, we also need this */ (_)

Awesome, right? I leave it up to you to figure out what the above piece of code does.

Don’t believe it? Or don’t care about the puzzle? Here’s the solution on ScalaFiddle.

This discussion was inspired by CTMMC