# Part 3: Checking and validating inputs · Your first Rell app on Chromia · Learn Chromia

> This lesson shows you how to validate input in Rell to make your app more secure. You add require checks to the create_book_review operation so it rejects…

Source: https://chromia.com/learn/book-review/input-verification/

Your first Rell app on ChromiaLesson 12 of 26

1. [01Your first Rell app on Chromia](https://chromia.com/learn/book-review/introduction/)
2. [02Set up your project](https://chromia.com/learn/book-review/setup/)
3. [03Rell project structure](https://chromia.com/learn/book-review/rell-structure/)

Part 1: Define your first entity

1. [04Overview](https://chromia.com/learn/book-review/book-entity/)
2. [05Create your first entity](https://chromia.com/learn/book-review/book-entity/tables/)
3. [06Add your first operation](https://chromia.com/learn/book-review/book-entity/basic-operations/)
4. [07Query every book](https://chromia.com/learn/book-review/book-entity/write-queries/)

Part 2: Add a related entity

1. [08Overview](https://chromia.com/learn/book-review/book-review-entity/)
2. [09Define the book review entity](https://chromia.com/learn/book-review/book-review-entity/tables/)
3. [10Add an operation for creating book reviews](https://chromia.com/learn/book-review/book-review-entity/basic-operations/)
4. [11Query all reviews for a book](https://chromia.com/learn/book-review/book-review-entity/write-queries/)

Part 3: Checking and validating inputs

1. [12Overview](https://chromia.com/learn/book-review/input-verification/)
2. [13Verify inputs](https://chromia.com/learn/book-review/input-verification/input-verification/)
3. [14Return structured results from queries](https://chromia.com/learn/book-review/input-verification/structure/)

Part 4: Signing transactions and filtering queries

1. [15Overview](https://chromia.com/learn/book-review/sign-transaction/)
2. [16Sign a transaction](https://chromia.com/learn/book-review/sign-transaction/sign-transaction/)
3. [17Filter and sort query results](https://chromia.com/learn/book-review/sign-transaction/structure/)

Part 5: Blockchain state and transactions explained

1. [18Overview](https://chromia.com/learn/book-review/blockchain-transactions/)
2. [19How blockchain state and transactions work](https://chromia.com/learn/book-review/blockchain-transactions/query-transaction/)
3. [20Walking through an example](https://chromia.com/learn/book-review/blockchain-transactions/example/)

Part 6: Create the client

1. [21Overview](https://chromia.com/learn/book-review/build-client/)
2. [22Prerequisites](https://chromia.com/learn/book-review/build-client/prerequisites/)
3. [23Establishing a connection to Chromia](https://chromia.com/learn/book-review/build-client/sign-transaction/)
4. [24Query the blockchain using postchain-client](https://chromia.com/learn/book-review/build-client/query-blockchain/)
5. [25Complete the example](https://chromia.com/learn/book-review/build-client/complete-example/)

1. [26What’s next?](https://chromia.com/learn/book-review/what-next/)

[Learn](https://chromia.com/learn/)[Your first Rell app on Chromia](https://chromia.com/learn/book-review/)

12 / 26Part 3: Checking and validating inputsBeginner

# Part 3: Checking and validating inputs

This lesson shows you how to validate input in Rell to make your app more secure. You add `require` checks to the `create_book_review` operation so it rejects invalid data, then write tests that cover both books that exist and books that don't.

You'll also shape query results with the `book_review_dto` struct, which packs book and review data into one organized object.

## In this lesson

1. [Verify inputs](https://chromia.com/learn/book-review/input-verification/input-verification/)
2. [Return structured results from queries](https://chromia.com/learn/book-review/input-verification/structure/)

[Begin lesson →](https://chromia.com/learn/book-review/input-verification/input-verification/)

Written for this site from Chromia’s public course. Code samples are the course’s own.

[← Previous**Query all reviews for a book**](https://chromia.com/learn/book-review/book-review-entity/write-queries/)[Next →**Verify inputs**](https://chromia.com/learn/book-review/input-verification/input-verification/)