---
layout: pattern
title: Data Transfer Object
folder: data-transfer-object
permalink: /patterns/data-transfer-object/
categories: Architectural
tags:
 - Performance
---

## Intent
Pass data with multiple attributes in one shot from client to server, to avoid multiple calls to remote server. 

## Explanation

Real world example

> We need to fetch information about customers from remote database. Instead of querying the attributes one at a time, we use DTOs to transfer all the relevant attributes in a single shot.     

In plain words

> Using DTO relevant information can be fetched with a single backend query. 

Wikipedia says

> In the field of programming a data transfer object (DTO) is an object that carries data between processes. The 
motivation for its use is that communication between processes is usually done resorting to remote interfaces 
(e.g., web services), where each call is an expensive operation. Because the majority of the cost of each call is 
related to the round-trip time between the client and the server, one way of reducing the number of calls is to use an 
object (the DTO) that aggregates the data that would have been transferred by the several calls, but that is served by 
one call only.

**Programmatic Example**

Let's first introduce our simple customer DTO class.

```java
public class CustomerDto {
  private final String id;
  private final String firstName;
  private final String lastName;

  public CustomerDto(String id, String firstName, String lastName) {
    this.id = id;
    this.firstName = firstName;
    this.lastName = lastName;
  }

  public String getId() {
    return id;
  }

  public String getFirstName() {
    return firstName;
  }

  public String getLastName() {
    return lastName;
  }
}
```

Customer resource class acts as the server for customer information.

```java
public class CustomerResource {
  private final List<CustomerDto> customers;

  public CustomerResource(List<CustomerDto> customers) {
    this.customers = customers;
  }

  public List<CustomerDto> getAllCustomers() {
    return customers;
  }

  public void save(CustomerDto customer) {
    customers.add(customer);
  }

  public void delete(String customerId) {
    customers.removeIf(customer -> customer.getId().equals(customerId));
  }
}
```

Now fetching customer information is easy since we have the DTOs.

```java
    var allCustomers = customerResource.getAllCustomers();
    allCustomers.forEach(customer -> LOGGER.info(customer.getFirstName()));
    // Kelly
    // Alfonso
```

## Class diagram
![alt text](./etc/data-transfer-object.urm.png "data-transfer-object")

## Applicability
Use the Data Transfer Object pattern when

* The client is asking for multiple information. And the information is related.
* When you want to boost the performance to get resources.
* You want reduced number of remote calls.

## Credits

* [Design Pattern - Transfer Object Pattern](https://www.tutorialspoint.com/design_pattern/transfer_object_pattern.htm)
* [Data Transfer Object](https://msdn.microsoft.com/en-us/library/ff649585.aspx)
* [J2EE Design Patterns](https://www.amazon.com/gp/product/0596004273/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596004273&linkCode=as2&tag=javadesignpat-20&linkId=f27d2644fbe5026ea448791a8ad09c94)
* [Patterns of Enterprise Application Architecture](https://www.amazon.com/gp/product/0321127420/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0321127420&linkCode=as2&tag=javadesignpat-20&linkId=014237a67c9d46f384b35e10151956bd)
