1	const createBook = async function (): Promise<boolean> {
2	  try {
3	    // These values come from state variables linked to
4	    // the screen form fields, retrieving the user choices
5	    // as a complete Parse.Object, when applicable;
6	    const bookTitleValue: string = bookTitle;
7	    const bookISBDValue: string = bookISBD;
8	    // For example, bookPublisher holds the value from
9	    // RadioButton.Group field with its options being every
10	    // Publisher parse object instance saved on server, which is
11	    // queried on screen load via useEffect
12	    const bookPublisherObject: Parse.Object = bookPublisher;
13	    const bookGenreObject: Parse.Object = bookGenre;
14	    // bookAuthors can be an array of Parse.Objects, since the book
15	    // may have more than one Author
16	    const bookAuthorsObjects: [Parse.Object] = bookAuthors;
17	
18	    // Creates a new parse object instance
19	    let Book: Parse.Object = new Parse.Object('Book');
20	
21	    // Set data to parse object
22	    // Simple title field
23	    Book.set('title', bookTitleValue);
24	
25	    // 1:1 relation, need to check for uniqueness of value before creating a new ISBD object
26	    let isbdQuery: Parse.Query = new Parse.Query('ISBD');
27	    isbdQuery.equalTo('name', bookISBDValue);
28	    let isbdQueryResult: Parse.Object = await isbdQuery.first();
29	    if (isbdQueryResult !== null && isbdQueryResult !== undefined) {
30	      // If first returns a valid object instance, it means that there
31	      // is at least one instance of ISBD with the informed value
32	      Alert.alert(
33	        'Error!',
34	        'There is already an ISBD instance with this value!',
35	      );
36	      return false;
37	    } else {
38	      // Create a new ISBD object instance to create a one-to-one relation on saving
39	      let ISBD: Parse.Object = new Parse.Object('ISBD');
40	      ISBD.set('name', bookISBDValue);
41	      ISBD = await ISBD.save();
42	      // Set the new object to the new book object ISBD field
43	      Book.set('isbd', ISBD);
44	    }
45	
46	    // One-to-many relations can be set in two ways:
47	    // add direct object to field (Parse will convert to pointer on save)
48	    Book.set('publisher', bookPublisherObject);
49	    // or add pointer to field
50	    Book.set('genre', bookGenreObject.toPointer());
51	
52	    // many-to-many relation
53	    // Create a new relation so data can be added
54	    let authorsRelation = Book.relation('authors');
55	    // bookAuthorsObjects is an array of Parse.Objects,
56	    // you can add to relation by adding the whole array or object by object
57	    authorsRelation.add(bookAuthorsObjects);
58	
59	    // After setting the values, save it on the server
60	    try {
61	      await Book.save();
62	      // Success
63	      Alert.alert('Success!');
64	      navigation.goBack();
65	      return true;
66	    } catch (error) {
67	      // Error can be caused by lack of Internet connection
68	      Alert.alert('Error!', error.message);
69	      return false;
70	    }
71	  } catch (error) {
72	    // Error can be caused by lack of value selection
73	    Alert.alert(
74	      'Error!',
75	      'Make sure to select valid choices in Publisher, Genre and Author fields!',
76	    );
77	    return false;
78	  }
79	};

1	const queryBooks = async function (): Promise<boolean> {
2	  // These values come from state variables linked to
3	  // the screen query RadioButton.Group fields, with its options being every
4	  // parse object instance saved on server from the referred class, which is
5	  // queried on screen load via useEffect; these variables retrievie the user choices
6	  // as a complete Parse.Object;
7	  const queryPublisherValue: Parse.Object = queryPublisher;
8	  const queryGenreValue: Parse.Object = queryGenre;
9	  const queryAuthorValue: Parse.Object = queryAuthor;
10	  const queryIsbdValue: Parse.Object = queryIsbd;
11	
12	  // Reading parse objects is done by using Parse.Query
13	  const parseQuery: Parse.Query = new Parse.Query('Book');
14	
15	  // One-to-many queries
16	  if (queryPublisherValue !== '') {
17	    parseQuery.equalTo('publisher', queryPublisherValue);
18	  }
19	  if (queryGenreValue !== '') {
20	    parseQuery.equalTo('genre', queryGenreValue);
21	  }
22	
23	  // One-to-one query
24	  if (queryIsbdValue !== '') {
25	    parseQuery.equalTo('isbd', queryIsbdValue);
26	  }
27	
28	  // Many-to-many query
29	  // In this case, we need to retrieve books related to the chosen author
30	  if (queryAuthorValue !== '') {
31	    parseQuery.equalTo('authors', queryAuthorValue);
32	  }
33	
34	  try {
35	    let books: [Parse.Object] = await parseQuery.find();
36	    // Many-to-many objects retrieval
37	    // In this example we need to get every related author Parse.Object
38	    // and add it to our query result objects
39	    for (let book of books) {
40	      // This query is done by creating a relation and querying it
41	      let bookAuthorsRelation = book.relation('authors');
42	      book.authorsObjects = await bookAuthorsRelation.query().find();
43	    }
44	    setQueriedBooks(books);
45	    return true;
46	  } catch (error) {
47	    // Error can be caused by lack of Internet connection
48	    Alert.alert('Error!', error.message);
49	    return false;
50	  }
51	};