SQL query builde example

QueryBuilderExample.java

public final class SearchCriteria {

	public enum Criterion {
		KUNDREF("kundRef"),
		LANSTILLHORIGHET("lanstillhorighet"),
		STODAR("stodar");

		// I only needed column name, no datatypes here
		private final String columnName;

		Criterion(final String columnName) {
			this.columnName = columnName;
		}

		public String getColumnName() {
			return columnName;
		}
	}
  
	public static final class SearchCriteriaBuilder {
		private final Map<Criterion, Object> criteriaMap = new HashMap<>();

		public SearchCriteriaBuilder stodar(final Stodar stodar) {
			criteriaMap.put(Criterion.STODAR, stodar);
			return this;
		}

		public SearchCriteriaBuilder kundRef(final KundRef kundRef) {
			criteriaMap.put(Criterion.KUNDREF, kundRef);
			return this;
		}

		public SearchCriteriaBuilder lanstillhorighet(final LanEnum lanstillhorighet) {
			criteriaMap.put(Criterion.LANSTILLHORIGHET, lanstillhorighet);
			return this;
		}

		public SearchCriteria build() {
			return new SearchCriteria(criteriaMap);
		} 
	}

	public static SearchCriteriaBuilder searchBuilder() {
		return new SearchCriteriaBuilder();
	}

	private final ImmutableSortedMap<Criterion, Object> immutableCriteriaMap;

	private SearchCriteria(final Map<Criterion, ?> criteria) {
		immutableCriteriaMap = ImmutableSortedMap.copyOf(criteria);
	}

	public ImmutableSortedMap<Criterion, Object> getCriteria() {
		return immutableCriteriaMap;
	}
}

// Usage example
public List<StodProjection> findByLanStodar(final Stodar stodar, final LanEnum lanstillhorighet) {
	checkNotNull(stodar, lanstillhorighet);
	SearchCriteria search = SearchCriteria.searchBuilder().stodar(stodar).lanstillhorighet(lanstillhorighet).build();

	final String jpqlString = QueryBuilder.buildSelectString(search);
	logger.info("Söker med JPQL:\n" + jpqlString + "\nMed input: " + search);

	final TypedQuery<StodProjection> query = buildTypedQuery(jpqlString, search);
	return query.getResultList();
}

Just det, buildTypedQuery behövdes eftersom JPA vill att man inte bara bygger en JPQL sats, men även binder variabler till den i en separat steg. Då har jag valt att låta buildSelectString(search) bygga själva JPQL med variabelnamn (lika med kolumnnamn i db), och buildTypedQuery(jpqlString, search) binda variabelvärde till variabelnamn.