activation rules for constraints not working for programming by contract

[spik3r]

Activation rules don't seem to work when using Programming by contract with AspectJ.
As per the documentation this works when using a Validator:

public class BusinessObject {
    private String fieldA;
    
    @NotNull(when = "javascript:_this.fieldA != null")
    private String fieldB;
    
    public BusinessObject(){}
    
    public BusinessObject(String fieldA, String fieldB) {
        this.fieldA = fieldA;
        this.fieldB = fieldB;
    }
    
    public String getFieldA() {
        return this.fieldA;
    }
    public void setFieldB(String fieldB) {
        this.fieldB = fieldB;
    }
}

But applying the same concept using Guarded does not.

@Guarded
public class Pojo {
    private String fieldA;
    private String fieldB;
    
    public Pojo(
            String fieldA,
            @NotNull(when = "javascript:_this.fieldA != null") String fieldB) {
        
        this.fieldA = fieldA;
        this.fieldB = fieldB;
    }
    
    public String getFieldA() {
        return this.fieldA;
    }
}

[sebthom]

Your example does not work because _this is a reference to the object you are about to create. The when expression is checked before the value of the argument fieldA is assigned to the field this.fieldA.

Activation of a parameter constraint depending on another parameter's value is currently not possible.

You can try using a @PostValidateThis constraint, e.g.

@Guarded
public class Pojo {
    private String fieldA;

    @NotNull(when = "javascript:_this.fieldA != null")
    private String fieldB;
    
    @PostValidateThis
    public Pojo(String fieldA, String fieldB) {
        this.fieldA = fieldA;
        this.fieldB = fieldB;
    }
    
    public String getFieldA() {
        return this.fieldA;
    }
}

[spik3r]

Hi Sebastian,
thanks for your quick response, unfortunately your code snipped doesn't work for me and throws a java.lang.StackOverflowError, unless I remove the getter. Unfortunately if I do that the JavaScript can't find the variable anymore

Is there some limitation to using @PostValidateThis?
It seems to only work when there is no when expression.
I think there may be a bug when using @PostValidateThis with when and either a public variable or getter since this exact combination always throws a java.lang.StackOverflowError even in a another example (slightly modified version of the example from 4.4.4 of the OVal documentation)

@Guarded
public class MethodPostValidation {
    
    private boolean someVariable = true;

    @MaxLength(value = 10)
//    @MaxLength(value = 10, when = "javascript:_this.someVariable == true") // Uncomment this to get StackOverflowError
    private String name = "12345";
    
    MethodPostValidation(){}
    
    MethodPostValidation(boolean someVariable) {
        this.someVariable = someVariable;
    }
    
    @PostValidateThis
    public void appendToName(String appendix) {
        name += appendix;
    }
    
    public boolean getSomeVariable() {
        return this.someVariable;
    }
}

Basic example tests:

public class MethodPostValidationTest {
    @Test(expected = ConstraintsViolatedException.class)
    public void getFieldTooLongThrowsException() throws Exception {
        MethodPostValidation methodPostValidation = new MethodPostValidation();
        methodPostValidation.appendToName("asdfghjkl");
        
    }
    
    @Test
    public void getFieldSomeVariableFalseDoesNotValidateNoException() throws Exception {
        MethodPostValidation methodPostValidation = new MethodPostValidation(false);
        methodPostValidation.appendToName("asdfghjkl");
    }
}

[sebthom]

I cannot really reproduce the issue. I extended the respective test case and it seems to work fine, see c676ef2

There are two things you need to be aware of:

1. The JavaScript Engine Rhino cannot directly access private fields. E.g. something like "javascript:_this.myPrivateField != null && _this.myPrivateField.length > 10" will always return false, no matter the value of the private field. Rhino apparently does not raise an exception if it cannot access the private field. I would recommend you to use groovy instead of javascript for constraint activation.
2. For most scripting runtimes (including JavaScript) the statement _this.someVariable will result in the invocation of the _this.getSomeVariable() getter and not in a direct access of a private field with the same name.

[spik3r]

Hi Sebastian,
thanks again.

I noticed that javascript couldn't see private variables for some reason.
I've got it working using @PostValidateThis as long as I add @Guarded(checkInvariants = false) otherwise I get a StackOverflowError from the getters.

@Guarded(checkInvariants = false)// removing this results in StackOverflowError
public class User {
    private final String firstName;
    private final String lastName;
    @NotNull(when = "groovy:_this.lastName != null")
    private final Integer age;

    @PostValidateThis
    public User(String firstName, String lastName, Integer age) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public Integer getAge() {
        return age;
    }
}

[sebthom]

I added a fix for the StackOverflowError. Can you please give the latest snapshot a try: http://oval.sourceforge.net/mvn-repo/snapshot/net/sf/oval/oval/1.88-SNAPSHOT/

[spik3r]

I've tested the latest snapshot and can confirm I no longer get the StackOverflowError.
Thanks again for the quick fix.