Added complex function test cases for JSqlParserQueryEnhancer.

The added test cases make sure the new implementation does not have the issue described in spring-projects#2441.

Closes spring-projects#2441

Author: DiegoKrupitza

src/main/java/org/springframework/data/jpa/repository/query/JSqlParserQueryEnhancer.java

@@ -139,6 +139,17 @@ private Set<String> getSelectionAliases(PlainSelect selectBody) {
 				.collect(Collectors.toSet());
 	}
 
+	/**
+	 * Returns the aliases used inside the selection part in the query.
+	 *
+	 * @return a {@literal Set} containing all found aliases. Guaranteed to be not {@literal null}.
+	 */
+	Set<String> getSelectionAliases() {
+		Select selectStatement = parseSelectStatement(this.query.getQueryString());
+		PlainSelect selectBody = (PlainSelect) selectStatement.getSelectBody();
+		return this.getSelectionAliases(selectBody);
+	}
+
 	/**
 	 * Returns the aliases used for {@code join}s.
 	 *

src/test/java/org/springframework/data/jpa/repository/query/QueryEnhancerUnitTests.java

@@ -649,6 +649,31 @@ void detectsJoinAliasesCorrectly(String queryString, List<String> aliases) {
 
 	}
 
+	@Test // GH-2441
+	void correctFunctionAliasWithComplexNestedFunctions() {
+		String queryString = "\nSELECT \nCAST(('{' || string_agg(distinct array_to_string(c.institutes_ids, ','), ',') || '}') AS bigint[]) as institutesIds\nFROM\ncity c";
+		StringQuery nativeQuery = new StringQuery(queryString, true);
+
+		JSqlParserQueryEnhancer queryEnhancer = (JSqlParserQueryEnhancer) getEnhancer(nativeQuery);
+
+		assertThat(queryEnhancer.getSelectionAliases()).contains("institutesIds");
+	}
+
+	@Test // GH-2441
+	void correctApplySortOnComplexNestedFunctionQuery() {
+		String queryString = "SELECT dd.institutesIds FROM (\n" + "                                SELECT\n"
+				+ "                                    CAST(('{' || string_agg(distinct array_to_string(c.institutes_ids, ','), ',') || '}') AS bigint[]) as institutesIds\n"
+				+ "                                FROM\n" + "                                    city c\n"
+				+ "                            ) dd";
+
+		StringQuery nativeQuery = new StringQuery(queryString, true);
+
+		QueryEnhancer queryEnhancer = getEnhancer(nativeQuery);
+
+		String result = queryEnhancer.applySorting(Sort.by(new Sort.Order(Sort.Direction.ASC, "institutesIds")));
+		assertThat(result).containsIgnoringCase("order by dd.institutesIds");
+	}
+
 	public static Stream<Arguments> detectsJoinAliasesCorrectlySource() {
 		return Stream.of( //
 				Arguments.of("select p from Person p left outer join x.foo b2_$ar", Collections.singletonList("b2_$ar")), //