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Git and this blog

2009-11-01T15:02:48Z

Writing this blog sometimes requires experimentation and other times requires exploration of alternatives. I use Git as the version control system (VCS) for this. Git is one of the new(er) generation distributed version control systems (DVCS). Git is quite powerful, but does require some time getting used to not only the commands but various workflows as well.

For my blog, alternative solutions go into their own branches. In fact, each entry goes into into own branch. If I decide to move ahead with the change in the master “blog” project(s), then I rebase the master branch. With Git I get all the benefits of a VCS with out much overhead: setting up server, committing partial work, having multiple versions, etc.

I would encourage you to give Git (or one of the newer DVCSs) a try for your real or toy projects.

Parameter IN clause in Hibernate

2009-10-15T16:43:28Z

I want to pass in a collection and use that collection in an IN clause. For example, given a collection of identifiers (ids), I want a collection of products that match those identifiers. Hibernate supports this by allowing the in clause to be a parameter as shown in the example below:

        1: Collection<Integer> aIds = Arrays.asList(p1.getId(), p2.getId(), p3.getId());

       2: ...

       3: String s = "select p from Product p where p.mId in (:aIds)";

       4: List<Product> aProducts = mManager.createQuery(s).setParameter("aIds", aIds).getResultList();

In the above example, aIds is the collection parameter used in the IN clause. The SQL generated by Hibernate is:

       1: select 

       2:     product0_.PRODUCT_ID as PRODUCT1_0_ 

       3: from 

       4:     PRODUCT product0_ 

       5: where 

       6:     product0_.PRODUCT_ID in (? , ? , ?)

Hibernate allows me to take this one step further. The Parameter IN clause can not only be primitive types but entities as well. For example, given a collection of products, I want a collection of order line items that match those products as shown in the example below:

       1: String aQuery = "select o from OrderLineItem o where o.mProduct in (:aProducts)";

       2: List<OrderLineItem> aOrderLineItems =

       3:         mManager.createQuery(aQuery).setParameter("aProducts", aProducts).getResultList();

In the above example, aProducts is the collection parameter used in the IN clause. The SQL generated by Hibernate is:

       1: select 

       2:     orderlinei0_.ORDER_LINE_ITEM_ID as ORDER1_2_, orderlinei0_.PRODUCT_ID as PRODUCT2_2_ 

       3: from 

       4:     ORDER_LINE_ITEM orderlinei0_ 

       5: where 

       6:     orderlinei0_.PRODUCT_ID in (? , ?)

Pretty cool!

Enum and Hibernate Mismatch?

2009-10-06T00:51:55Z

Hibernate nicely supports enum ordinal type and string type out of the box as defined in the Java Persistence API (JPA) specification. But, sometimes with legacy databases you need custom enum mapping.

There is lot of information out there, but the following are the two most useful:

So much meta information is specified for a simple enum in the above links. Wow! Something just doesn’t feel right about it. If I default / hardcode the identifierMethod and valueOfMethod, I can get it look like the following:

        1: @Column(name = "ORDER_TYPE")

       2: @Type(type = "ms.EnumUserType",

       3:         parameters = {@Parameter(name = "enumClass", value = "ms.domain.Order$OrderType")})

       4: private OrderType mOrderType;

Still, I am specifying redundant information in value because I should be able to figure that out by the declared type of the member variable OrderType in this case.

Multiple Hamcrest versions?

2009-10-03T20:37:50Z

I am using the following:

junit4.7.jar
hamcrest-all-1.2.jar

When the test failed I got the following exception:

        1: java.lang.NoSuchMethodError: org.hamcrest.Matcher.describeMismatch(Ljava/lang/Object;Lorg/hamcrest/DescriptionV

       2:     at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)

       3:     at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:8)

       4:     at ms.EnumExample.saveEnum(EnumExample.java:19)

       5:     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

       6:     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

       7:     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

       8:     at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)

       9:     at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)

      10:     at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)

      11:     at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)

      12:     at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)

      13:     at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)

      14:     at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:76)

      15:     at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)

      16:     at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)

      17:     at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)

      18:     at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)

      19:     at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)

      20:     at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)

      21:     at org.junit.runners.ParentRunner.run(ParentRunner.java:236)

      22:     at com.intellij.rt.junit4.Junit4TestMethodAdapter.run(Junit4TestMethodAdapter.java:62)

      23:     at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:40)

      24:     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

      25:     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

      26:     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

      27:     at com.intellij.rt.execution.application.AppMain.main(AppMain.java:90)

I guess hamcrest ships with JUnit.

One solution is to download junit-dep-4.7.jar and make it part of the project. Then everything works fine!

Another solution that I haven’t tried is to remove hamcrest jar and just rely on junit 4.7, unless of course you need something specific from the version of hamcrest.

Using Embeddable, Embedded, and Secondary Table instead One-to-One (in Hibernate)

2009-09-28T15:11:54Z

In my last blog entry, I discussed One-to-One relationship in Hibernate. The problem was the extra SQL statements! One solution is to use Embeddable and Embedded concepts.

The ProductDescription becomes an Embeddable instead of an entity. Other than that, it pretty much remains the same as shown below.

        1: @Embeddable

       2: public class ProductDescription implements Serializable {

       3:     @Column(name = "DESCRIPTION", table = "PRODUCT_DESC"

       4:     private String mDescrption;

       5:  

       6:     ...

       7: }

The Product instead of having one-to-one, has an embedded ProductionDescription. I also indicate the secondary table with @SecondaryTable annotation.

       1: @Entity

       2: @Table(name = "PRODUCT")

       3: @SecondaryTable(name = "PRODUCT_DESC")

       4: public class Product {

       5:     ...

       6:  

       7:     @Embedded

       8:     private ProductDescription mProductDescription;

       9:  

      10:     ...

      11: }

Running with the same example as in the previous blog entry, the SQL generated includes an outer join and the number of SQL statements is reduced!

       1: select 

       2:     product0_.PRODUCT_ID as PRODUCT1_0_, product0_1_.DESCRIPTION as DESCRIPT1_1_ 

       3: from 

       4:     PRODUCT product0_ 

       5:     left outer join PRODUCT_DESC product0_1_ on product0_.PRODUCT_ID=product0_1_.PRODUCT_ID

In the previous blog entry, I mentioned, almost lamented, about all those blog entries and forum posts that describe the problem, but no decent solution. Now, you can include this blog entry to that list!

One-to-One in Hibernate

2009-09-26T20:47:27Z

Consider the following one-to-one relationship between Product and ProductDescription: Product can have optional ProductDescription. The following is the Product side:

        1: public class Product {

       2:     ...

       3:  

       4:     @OneToOne(mappedBy = "mProduct", fetch = FetchType.LAZY, optional = true)

       5:     private ProductDescription mDescription;

       6:  

       7:     ...

       8: }

The following is the ProductDescription side:

       1: public class ProductDescription {

       2:     ...

       3:  

       4:     @OneToOne(optional = false)

       5:     @JoinColumn(name = "PRODUCT_ID")

       6:     private Product mProduct;

       7:  

       8:     ...

       9: }

Assuming the product table contains two products. One without description and one with description. Hibernate generates the following SQL:

       1: select product0_.PRODUCT_ID as PRODUCT1_0_ from PRODUCT product0_

       2: select productdes0_.PRODUCT_ID as PRODUCT1_1_1_, productdes0_.DESCRIPTION as DESCRIPT2_1_1_, product1_.PRODUCT_ID as PRODUCT1_0_0_ from PRODUCT_DESC productdes0_ inner join PRODUCT product1_ on productdes0_.PRODUCT_ID=product1_.PRODUCT_ID where productdes0_.PRODUCT_ID=?

       3: select productdes0_.PRODUCT_ID as PRODUCT1_1_1_, productdes0_.DESCRIPTION as DESCRIPT2_1_1_, product1_.PRODUCT_ID as PRODUCT1_0_0_ from PRODUCT_DESC productdes0_ inner join PRODUCT product1_ on productdes0_.PRODUCT_ID=product1_.PRODUCT_ID where productdes0_.PRODUCT_ID=?

The ProductDescription in Product is lazy, so why does hibernate try to load the descriptions?

The are many blogs, forum messages, etc. for this problem. They describe hacks and other ideas, but none of them is quite acceptable.

Syntactic Sugar with Hamcrest

2009-09-24T21:22:50Z

Do you love sugar? Syntactic Sugar? If you do then you would like Hamcrest. Hamcrest makes unit tests little more readable.

The following is a simple JUnit test:

        1: @Test

       2: public void SimpleBoolean() {

       3:     assertEquals(true, coolTest());        

       4: }

Now, using Hamcrest:

       1: @Test

       2: public void SimpleBoolean_Hamcrest() {

       3:     assertThat(coolTest(), is(true));

       4: }

Notice the usage of static imports in both the versions. Also, in the Hamcrest version the actual and expected are switched. Some people think that the Hamcrest version is more natural. Is this syntactic sugar worth it? To help you decide checkout the following additional example:

       1: @Test

       2: public void Comparison() {

       3:     assertEquals(true, commission() > 10);

       4: }

The Hamcrest version is:

       1: @Test

       2: public void Comparison_Hamcrest() {

       3:     assertThat(commission(), is(greaterThan(10)));

       4: }

The following is an example of comparing BigDecimals. Usually, code like this is pretty ugly.

       1: @Test

       2: public void CompareBigDecimal() {

       3:     assertEquals(true, new BigDecimal("0.99").compareTo(price()) == 0);

       4: }

And the Hamcrest version:

Note: Just ordering comparison was added in the later version of Hamcrest.

       1: @Test

       2: public void CompareBigDecimal_Hamcrest() {

       3:     assertThat(price(), comparesEqualTo(new BigDecimal("0.99")));

       4: }

I have seen code that uses Hamcrest assertThat as assertEquals, but I think that defeats the purpose. In this case, may be the developer is missing the point of syntactic sugar?

Eliminate String Concatenation

2009-09-19T19:18:08Z

Consider the following piece of code that does string concatenation.

        1: public String validateOrderLineItem(OrderLineItem aOrderLineItem) {

       2:     if (aOrderLineItem.getPrice() == null) {

       3:         return "The order line item for product: " + aOrderLineItem.getProduct().getDescription() +

       4:                 " for order id : " + aOrderLineItem.getOrder().getId() + " must not be null!";

       5:     }

       6:     return null;

       7: }

I am not a big fan of such string concatenation. Such strings are harder to read and maintain. They are also potential performance and memory problems.

I always try to replace the code above with something that looks like this:

       1: private static final String INVALID_PRICE =

       2:         "The order line item for product: %s  for order id : %s  must not be null!";

       3:  

       4: public String validateOrderLineItem2(OrderLineItem aOrderLineItem) {

       5:     if (aOrderLineItem.getPrice() == null) {

       6:         return String.format(INVALID_PRICE, aOrderLineItem.getProduct().getDescription(),

       7:                 aOrderLineItem.getOrder().getId());

       8:     }

       9:     return null;

      10: }

At least the message is much easier to read!

There are couple of other alternatives like using MessageFormat and templating languages, but they are over kill for this example.

This example is in Java, but is equally applicable to C# and other languages.

Validation and Close / Cancel in WinForms

2009-09-12T16:46:17Z

I added a error provider in a form and added some validation logic. But, when I want to cancel and close the form, the form doesn’t close until the error is fixed. The way to fix this to set the Cancel property of the form closing event to be false.

How about if I have a cancel button and would like the same behavior as above? The trick now is to set the CausesValidation property of the cancel button to be false. Now, if you try this and it still doesn’t work, then just make sure that all the (parent) containers, excluding the form, of the cancel button also have the CausesValidation property as false.

Parameterized Method

2009-09-09T15:35:53Z

One of the dependency-breaking techniques described by Michael C. Features in his book “Working Effectively With Legacy Code” is Parameterized Method. I use this quite often to make code testable. My typical usage looks something like the following. Let’s say, I have the following method:

        1: public void ComplicatedMethod(View view)

       2: {

       3:     // some code here

       4:     if (view.Available) 

       5:         Console.WriteLine("more complicate code");

       6:     // even more complicated code

       7: }

What makes it hard to test this method is the instance of view. The view might not be easy to create. The view may have its own dependencies and so forth. However, notice how the view is being used. The view is only being used to check for a condition. So, let’s apply Parameterized Method refactoring to it.

       1: public void ComplicatedMethod(View view)

       2: {

       3:     ComplicatedMethod(view.Available);

       4: }

       5:  

       6: public void ComplicatedMethod(bool available)

       7: {

       8:     // some code here

       9:     if (available)

      10:         Console.WriteLine("more complicate code");

      11:     // even more complicated code

      12: }

Now, the over-loaded method that takes a bool instead of the view is easy to test!

The above example is in C#, but equally applicable to Java or anything else for that matter. There are many other alternatives to Parameterized Method as well.

Enums in Web Services

2009-08-25T16:13:40Z

I created a XSD where one of the fields is enum. Using the XSD, I created a WSDL. Using svcutil.exe, I generated the C# classes. If we ask C# to unmarshall an XML that is expecting an enum, but does not contain that enum value, then XMLSerializer picks the first enum value. The solution is to set a (default) value in the code, so there is a value for the XMLSerializer to unmarshall. Or, when declaring an element of the enum type in XSD make it nillable.

Setting up existing web application project in Eclipse

2009-08-24T15:24:23Z

I checked out an existing web project from the version control system. How do I setup this web project in Eclipse? There is no simple way! I can setup the project as existing Java project and use a hack to convert into a web (WTP) project. The hack is described here. A nice blog that describes the process with pictures is here. This feature should really be in Eclipse.

String Bean in Spring

2009-08-18T18:27:31Z

Have you wondered how to declare a bean of type string in Spring’s context? The following shows an example:

        1: <bean id="databaseSchema" class="java.lang.String">

       2:     <constructor-arg value="MyDatabaseSchema"></constructor-arg>

       3: </bean>

The above code declares a Spring bean named databaseSchema with a value of MyDatabaseSchema.

VM Arguments in Eclipse

2009-08-17T15:01:40Z

There are multiple different ways to set the VM arguments in Eclipse. The arguments can be set globally at the JDK level. In Eclipse, go to Window > Preferences > Java > Installed JREs as shown below.

Or, the VM argument can bet set at the Run / Debug configuration level as shown below.

When, I find that I am setting the VM arguments over and over again, then I move them to the global level.

Can’t debug in Eclipse / Can't allocate jvmti memory

2009-08-07T15:20:42Z

In Eclipse the debugger would refuse to launch. I tried many-many times to debug my application with no luck. Couple of times, I saw the following error message:

JDWP exit error JVMTI_ERROR_WRONG_PHASE(112): on getting class status [../../../src/share/back/util.c:1265]
JDWP exit error JVMTI_ERROR_INVALID_ENVIRONMENT(116): Can't allocate jvmti memory [../../../src/share/back/util.c:1779]
ERROR: JDWP unable to dispose of JVMTI environment: JVMTI_ERROR_INVALID_ENVIRONMENT(116)

Increasing the memory with –Xms and –Xmx (when launching the unit test, in this case) helped and I am able to launch the debugger in Eclipse.

How Agile are you?

2009-08-06T14:50:02Z

How Agile are you? Alistair Cockburn address this question in the book: Agile Software Development: The Cooperative Game, Second Edition. He lists criteria for agility and I would recommend using his Figure 5.1-19: A way to track projects’ use of the agile ideas. An important anecdote in the same section of the book is when a project is evaluated to be highly agile, but hasn’t delivered software in two years!

There is old saying that “beauty is in the eye of the beholder”, so is agility, I guess…

Save Actions in Eclipse

2009-08-05T00:08:02Z

I always optimize imports in Eclipse. Also, I format the code as well… Now, that only takes a couple of short-cut keys. But, both of these processes can be completely automated with Save Actions feature in Eclipse as shown below:

Whenever I save the file, Eclipse is going to perform the above actions, which is actually more that what I usually do… But, that is completely configurable.

Reference / library Dlls

2009-08-03T15:21:08Z

A project refers to many dlls. How are these dlls referenced? They can be loaded from GAC. Or, they could be relatively referenced. For the dlls that are relatively referenced, my suggestion is to create a lib (or whatever name) inside the project and then make them relative to that directory. Do not make these dlls be referenced from random paths on a particular developers computer!

Downloading JDK on Solaris?

2009-07-30T15:29:33Z

Going to the download page for the latest JDK for Solaris shows the following installs available:

So, sh and tars are the same, but why are two versions available for each .sh (and tar.Z)? One is the full install while the other is an overlay on an existing installing in a specific directory. The full install makes sense to me in most cases…

Test project and app.config

2009-07-28T15:33:52Z

How can the test project access the application’s app.config? For the test project to have access to app.config, the app.config at run-time must be available to it as <TestProjectName>.dll.config. There are multiple ways to accomplish this goal. The following describes one way:

Have the app.config be copied to bin/Debug folder of the test project. Edit Solution Items – LocalTestRun.config (or something similar). Go to Deployment. Add app.config as additional file to deploy.
Move app.config to <TestProjectName>.dll.config. On the test project add a post build event such as the following: move /Y "$(TargetDir)app.config" "$(TargetDir)$(ProjectName)$(TargetExt).config"