Transform SimpleExpresion/LogicalExpression in JPA

Hibernate ORM
1

Hi,

I have legacy code and a method that looks like this:

public List<ENTITY> findByCriteria(final Map<String, Object> criteriaMap, final List<String> fields, final Class<ENTITY> entityClass) {

	final Criteria criteria = this.getSession().createCriteria(entityClass);
	final Set<String> keys = criteriaMap.keySet();

	Object object;
	CriteriaValue criteriaValue;
	CriteriaValue.Operator operator;

	for (String key:keys) {
		object = criteriaMap.get(key);

		if (object instanceof SimpleExpression) {
			criteria.add((SimpleExpression)object);
		} else if (object instanceof LogicalExpression) {
			criteria.add((LogicalExpression)object);
		} else if (object instanceof Criterion) {
			criteria.add((Criterion)object);
		} else if (!isDefaultCriteria(key)) {
		...
	}
...
}

Is there a way to transform the if-clauses to JPA CriteriaBuilder? Or more specific, hat’s the equivalent of SimpleExpression/LogicalExpression in JPA?

What I would do is to try to transform the SimpleExpression into a Predicate like this:

protected SimpleExpression(String propertyName, Object value, String op) {
	this.propertyName = propertyName;
	this.value = value;
	this.op = op;

	protected final String getOp() {
		return op;
	}

	public String getPropertyName() {
		return propertyName;
	}

	public Object getValue() {
		return value;
	}
}

public Predicate simpleExpressionToPredicateTransformer(SimpleExpression simpleExpression)
	switch (simpleExpression.getOp()) {
		case EQ:
			// create and return predicate
		case iLIKE:
			// create and return predicate
		case LIKE:
			// create and return predicate
		case LE:
			// create and return predicate
	}
}

But unfortunately, the .getOp() method in SimpleExpression is protected and I cannot access it.

2

Just for completeness, here’s the CriteriaValue class

public class CriteriaValue implements Serializable {
		
	private static final long serialVersionUID = -5305816199528069626L;
	
	public enum Type {    	    			
		TEXT, 
		NUMBER,
		DATE 
	}
	
	/**
	 * The Enum Operator.
	 */
	public enum Operator {
    		    
	    EQ, 
		iLIKE, 
		LIKE, 
		LE, 
		GE, 
		LT, 
		GT,
		OR,
		AND
		IN,				
		NE,
	}
		
	private Object value;	
	
	private Type type;	
	
	private Operator operator;
	
	private String key;
	
	// Getters and setters omitted
}
3

You should avoid using the legacy Hibernate Criteria API as it was removed in Hibernate 6 and is deprecated for a while now. With your custom expression/criteria objects, you can do whatever you want and create appropriate JPA Criteria objects by using CriteriaBuilder.

4

Hi Beikov,

thanks for your reply. I’m migrating an existing Hibernate 3 app to version 5 and the usage of criteria api unfortunately took place years ago and needs to be migrated now. Could you please elaborate on what that means?

With your custom expression/criteria objects, you can do whatever you want and create appropriate JPA Criteria objects by using CriteriaBuilder.

I’m trying to write a transformer method from Hibernates legacy Criteria API to CriteriaBuilder but I don’t know how to extract the required information from a Criteria.

The SimpleExpression and Logical Expressions are not a problem anymore, as they were only used on 2 occasions. I did migrate these occasions to CriteriaBuilder. Butt the legacy Criterias are used throughout our app and rewriting the occurrences seems not to be feasible at the moment. That’s why I would like to write some kind of interceptor that transforms the Criteria to CriteriaQuery.

5

There are many tutorials on the internet that explain how the JPA Criteria API works:

You can copy the classes(LogicalExpression, etc.) from Hibernate that you use in your app, and then do a refactoring in your source tree to rename/move to your own package. Now you have classes that you can simply change and expose the getOp method, which you can then use to implement the transformation.

6

Ah ok, got it. Thank you!