Polishing.

Extend Javadoc, attempt join alias name generation using the initial candidate instead of immediate fallback to generic join_nnn naming.

See #3989

Author: mp911de

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/JpqlQueryBuilder.java

@@ -138,10 +138,34 @@ Selection postProcess(Selection selection) {
 	private static String getAlias(String from, java.util.function.Predicate<String> predicate,
 			Supplier<String> fallback) {
 
-		char c = from.toLowerCase(Locale.ROOT).charAt(0);
-		String string = Character.toString(c);
-		if (Character.isJavaIdentifierPart(c) && predicate.test(string)) {
-			return string;
+		StringBuilder builder = new StringBuilder();
+
+		char[] charArray = from.toLowerCase(Locale.ROOT).toCharArray();
+		for (char c : charArray) {
+
+			if (Character.isJavaIdentifierPart(c)) {
+				builder.append(c);
+			} else {
+				break;
+			}
+		}
+
+		if (builder.isEmpty()) {
+			return fallback.get();
+		}
+
+		String identifier = builder.toString();
+		String firstChar = identifier.substring(0, 1);
+
+		if (predicate.test(firstChar)) {
+			return firstChar;
+		}
+
+		for (int i = 0; i < 10; i++) {
+			String candidate = firstChar + "_" + i;
+			if (predicate.test(candidate)) {
+				return candidate;
+			}
 		}
 
 		return fallback.get();

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/JpqlQueryCreator.java

@@ -20,15 +20,35 @@
 import org.springframework.data.domain.Sort;
 
 /**
+ * Strategy interface that allows implementations to create JPQL queries providing details about parameter bindings and
+ * the selection mechanism.
+ *
  * @author Mark Paluch
+ * @since 4.0
  */
 interface JpqlQueryCreator {
 
+	/**
+	 * @return whether the query uses a tuple query.
+	 */
 	boolean useTupleQuery();
 
+	/**
+	 * Create the JPQL query applying {@link Sort}.
+	 *
+	 * @param sort the sort order, can be {@link Sort#unsorted()}.
+	 * @return the rendered JPQL query.
+	 */
 	String createQuery(Sort sort);
 
+	/*
+	 * @return the parameter bindings.
+	 */
 	List<ParameterBinding> getBindings();
 
+	/**
+	 * @return parameter binder to use to bind parameters.
+	 */
 	ParameterBinder getBinder();
+
 }

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/query/JpaQueryCreatorTests.java

@@ -676,7 +676,7 @@ void matchSameEntityMultipleTimesViaDifferentProperties() {
 				.withParameters(10, "spring") //
 				.as(QueryCreatorTester::create) //
 				.expectJpql(
-						"SELECT o FROM %s o LEFT JOIN o.lineItems l LEFT JOIN l.product p LEFT JOIN l.product2 join_0 WHERE p.name = ?1 AND join_0.name = ?2",
+						"SELECT o FROM %s o LEFT JOIN o.lineItems l LEFT JOIN l.product p LEFT JOIN l.product2 p_0 WHERE p.name = ?1 AND p_0.name = ?2",
 						DefaultJpaEntityMetadata.unqualify(Order.class)) //
 				.validateQuery();
 	}

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/query/JpqlQueryBuilderUnitTests.java

@@ -224,7 +224,7 @@ void joinOnPaths() {
 		String fragment = JpqlQueryBuilder.where(productName).eq(literal("ex30"))
 				.and(JpqlQueryBuilder.where(personName).eq(literal("cstrobl"))).render(ctx(entity));
 
-		assertThat(fragment).isEqualTo("p.name = 'ex30' AND join_0.name = 'cstrobl'");
+		assertThat(fragment).isEqualTo("p.name = 'ex30' AND p_0.name = 'cstrobl'");
 	}
 
 	@Test // GH-3989
@@ -310,8 +310,10 @@ static class LineItem {
 
 	@jakarta.persistence.Entity
 	static class Person {
+
 		@Id Long id;
 		String name;
+
 	}
 
 	@jakarta.persistence.Entity(name = "my_product")