Use Regular Expressions in JPA CriteriaBuilder

Question

I'm using the JPA CriteriaBuilder to select entities of type MyEntity from a MySQL db as follows:

String regExp = "(abc|def)"
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery query = cb.createQuery( MyEntity.class );
root = query.from( MyEntity.class );
predicates = new ArrayList<Predicate>();

predicates.add( cb.like( root.<String>get( "name" ), regExp ) );

Thus, the query result should contain any entity where the name value matches the given regExp. But the result list is always empty. Changing the regExp to /(abc|def)/g has no effect, neither does adding the wildcard %

How to make the pattern matching work?

Alternatively: How can I use native MySQL REGEXP together with the CriteriaBuilder?

Answer 1

Pattern matching in JPA queries is limited only to

• _ - any character
• % - any string

REGEXP has operator syntax in MySQL (SELECT 'a' REGEXP 'A') so it cannot be used with CriteriaBuilder.function() API. I'm afraid the best is to run native SQL query.

If you are using Hibernate you have one more option. You can wrap REGEXP operator in SQLFunctionTemplate, extend hibernate dialect and run with CriteriaBuilder.function().

Answer 2

I came across this recently and used the first post to implement the hibernate mysql function option.

To help save some time for others this is what I did:

set up the function in your custom dialect file in hibernate:

public class MySQLDialect extends Dialect {

   public MySQLDialect() {
      super();
      ...
      registerFunction("regexp", new SQLFunctionTemplate(StandardBasicTypes.INTEGER, "?1 REGEXP ?2"));
      ...
   }
   ...
}

then within the criteria builder section:

CriteriaBuilder builder = ...;    

Pattern regexPattern = Pattern.compile("^[0-9]\\|[0-9]+");

Expression<String> patternExpression = builder.<String>literal(regexPattern.pattern());

Path<String> path = ... ;// regex comparison column

// regexp comes from the name of the regex function 
// defined in the Mysql Dialect file above
Predicate theRegexPredicate = builder.equal(builder.function("regexp", Integer.class, path, patternExpression), 1);

Then use theRegexPredicate to construct the where clause in your CriteriaBuilder query.