EntityQuery.setRestrictions and Ejbql with parameters

Question

Hello.

It would be nice if anybody could show me how to use setRestrictions method whitch belongs to the EntityQuery object from the org.jboss.seam.framework.EntityQuery package.

I have tried to use it this way:

...
import org.jboss.seam.framework.EntityQuery;
import org.jboss.seam.core.Expressions.ValueExpression;

public class LetterList extends EntityQuery<Letter>
{
    public LetterList()
    {
        setEjbql("select letter from Letter letter");
    }

    public void sampleMethod(){              
        List<ValueExpression> restrictions = new ArrayList<ValueExpression>();
        restrictions.add(createValueExpression("letter.id=7"));
        setRestrictions(restrictions);          
    }

}

However, this piece of code throws an exception.

The following lines lead to error too:

String[] RESTRICTIONS = {"letter.id=7"};
setRestrictionExpressionStrings(Arrays.asList(RESTRICTIONS));

It is also interesting if it is possible to pass any parameters the nice way while using setEjbql. I mean whether it is possible to avoid concatenation.

I have really tried to find some examples of relevant code, but in vain. So, I would highly appreciate a few lines of code that work.

Answer 1

Try the following example:

@Name("letterList") // (1)
public class LetterList extends EntityQuery<Letter> {

    private Long letterId;

    public LetterList() {
        setEjbql("select letter from Letter letter");
        setRestrictionExpressionStrings(Arrays.asList(new String[] {
            "letter.id = #{letterList.letterId}" // (2)
        }));
    }

    public Long getLetterId() { // (3)
        return letterId;
    }
    public void setLetterId(Long letterId) {
        this.letterId = letterId;
    }
}

Note the three comment locations:

1. The @Name annotation declares your class as a seam component.
2. Each restriction expression must contain exactly one expression to be evaluated, no less and no more. It cannot be used with a constant like in your example.
3. You need to define a getter for each property that you reference in the restriction expressions.