fix: Add support for EQ,NE predicates for nullable scalar type values (#301)

* fix: Add support for EQ,NE predicates with null values

* fix: add more tests

* fix: apply null value predicate only for scalar values

Author: igdianov

graphql-jpa-query-schema/src/main/java/com/introproventures/graphql/jpa/query/schema/impl/JpaPredicateBuilder.java

@@ -729,6 +729,15 @@ private Predicate getTypedPredicate(From<?,?> from, Path<?> field, PredicateFilt
 
         if (type.isPrimitive())
             type = PRIMITIVES_TO_WRAPPERS.get(type);
+
+        if (NullValue.class.isInstance(value) && WRAPPERS_TO_PRIMITIVES.get(type) != null) {
+            if (criterias.contains(Criteria.EQ)) {
+                return cb.isNull(field);
+            } else if (criterias.contains(Criteria.NE)) {
+                return cb.isNotNull(field);
+            }
+        }
+
         if (type.equals(String.class)) {
             return getStringPredicate((Path<String>)field, filter);
         }

graphql-jpa-query-schema/src/test/java/com/introproventures/graphql/jpa/query/schema/GraphQLExecutorTests.java

@@ -559,6 +559,37 @@ public void queryAuthorBooksByAlliasesWithInlineWhereSearch() {
         assertThat(result.toString()).isEqualTo(expected);
     }
 
+    @Test
+    public void queryAuthorBooksWithNotNullFalseId() {
+        //given
+        String query = "query { "
+                + "Authors(" +
+                "    where: {" +
+                "      books: {" +
+                "        id: {NOT_NULL: false}" +
+                "      }" +
+                "    }" +
+                "  ) {" +
+                "    select {" +
+                "      id" +
+                "      name" +
+                "      books {" +
+                "        id" +
+                "        title" +
+                "        genre" +
+                "      }" +
+                "    }" +
+                "  }"
+                + "}";
+
+        String expected = "{Authors={select=[{id=8, name=Igor Dianov, books=[]}]}}";
+
+        //when
+        Object result = executor.execute(query).getData();
+
+        // then
+        assertThat(result.toString()).isEqualTo(expected);
+    }
     @Test
     public void queryAuthorBooksWithIsNullId() {
         //given
@@ -591,6 +622,109 @@ public void queryAuthorBooksWithIsNullId() {
         assertThat(result.toString()).isEqualTo(expected);
     }
 
+    @Test
+    public void queryAuthorBooksWithEQNullId() {
+        //given
+        String query = "query { "
+                + "Authors(" +
+                "    where: {" +
+                "      books: {" +
+                "        id: {EQ: null}" +
+                "      }" +
+                "    }" +
+                "  ) {" +
+                "    select {" +
+                "      id" +
+                "      name" +
+                "      books {" +
+                "        id" +
+                "        title" +
+                "        genre" +
+                "      }" +
+                "    }" +
+                "  }"
+                + "}";
+
+        String expected = "{Authors={select=[{id=8, name=Igor Dianov, books=[]}]}}";
+
+        //when
+        Object result = executor.execute(query).getData();
+
+        // then
+        assertThat(result.toString()).isEqualTo(expected);
+    }
+
+    @Test
+    public void queryAuthorBooksWithNENullId() {
+        //given
+        String query = "query { "
+                + "Authors(" +
+                "    where: {" +
+                "      books: {" +
+                "        id: {NE: null}" +
+                "      }" +
+                "    }" +
+                "  ) {" +
+                "    select {" +
+                "      id" +
+                "      name" +
+                "      books {" +
+                "        id" +
+                "        title" +
+                "        genre" +
+                "      }" +
+                "    }" +
+                "  }"
+                + "}";
+
+        String expected = "{Authors={select=[" +
+                "{id=1, name=Leo Tolstoy, books=[{id=2, title=War and Peace, genre=NOVEL}, {id=3, title=Anna Karenina, genre=NOVEL}]}, " +
+                "{id=4, name=Anton Chekhov, books=[{id=5, title=The Cherry Orchard, genre=PLAY}, {id=6, title=The Seagull, genre=PLAY}, {id=7, title=Three Sisters, genre=PLAY}]}" +
+        "]}}";
+
+        //when
+        Object result = executor.execute(query).getData();
+
+        // then
+        assertThat(result.toString()).isEqualTo(expected);
+    }
+
+
+    @Test
+    public void queryAuthorBooksWithNOT_NULLId() {
+        //given
+        String query = "query { "
+                + "Authors(" +
+                "    where: {" +
+                "      books: {" +
+                "        id: {NOT_NULL: true}" +
+                "      }" +
+                "    }" +
+                "  ) {" +
+                "    select {" +
+                "      id" +
+                "      name" +
+                "      books {" +
+                "        id" +
+                "        title" +
+                "        genre" +
+                "      }" +
+                "    }" +
+                "  }"
+                + "}";
+
+        String expected = "{Authors={select=[" +
+                "{id=1, name=Leo Tolstoy, books=[{id=2, title=War and Peace, genre=NOVEL}, {id=3, title=Anna Karenina, genre=NOVEL}]}, " +
+                "{id=4, name=Anton Chekhov, books=[{id=5, title=The Cherry Orchard, genre=PLAY}, {id=6, title=The Seagull, genre=PLAY}, {id=7, title=Three Sisters, genre=PLAY}]}" +
+                "]}}";
+
+        //when
+        Object result = executor.execute(query).getData();
+
+        // then
+        assertThat(result.toString()).isEqualTo(expected);
+    }
+
     @Test
     public void queryBooksAuthorWithExplictOptionalTrue() {
         //given