I have a Userdetails class like the one below
public class UserDetails
{
public string ssn;
public string username;
public string emailid;
public Address address;
}
Here Address is another class that will have public fields like
public class Address
{
public int id;
public string address;
}
Now, when the user logs in the app, i construct the Userdetails object. Now i will not use address object inside the userdetails very frequently, but have got data.
In this scenario how can i use the Lazy initialization feature of C# 4.0.
Note that the data is taken from direct db query and none of these classes have constructors or other means to get the data. These are just representations of the database fields in C#.
Suggest me the best way to use lazy initialization here.
You can have a private lazy address:
private Lazy<Address> _address = new Lazy<Address>(() => {
---code to get the address---
});
public Address address {
get {
return _address.Value;
}
}
Related
Say I have some Brands, each Brand have some Products. When define Entity follow CQRS pattern, is it good practice having List<Product> as a field of Brand? Or one Entity should never hold another Entity, I need to define another Entity BrandProductRelationship?
public class Brand {
private String id;
private String name;
private List<Product> products;
}
public class Product {
private String id;
private String name;
}
If so, when define brand created event, looks like I need to pass List<Product> as a parameter, which seems complicate.
public class BrandCreated implements Event {
public Brand apply() {
return new Brand(id, name, products);
}
}
Entities that contain other entities is fine, provided that they are all part of the same consistency boundary.
The story is different with aggregates; you don't normally want to have two different paths to modify the state of a single specific entity, so having one aggregate contain another is discouraged. In this case, you'll normally have one aggregate contain an identifier that can be used to look up the other.
public class Brand {
private String id;
private String name;
private List<String> productsIds;
}
Is better; but it demonstrates primitive obsession. In Domain Driven Design, entities are more likely to be expressed using values from the domain model itself.
public class Brand {
private Identifier<Brand> id;
private Name name;
private List<ProductId> productsIds;
}
or even
public class Brand {
private Identifier<Brand> id;
private Name name;
private ProductCatalog catalog;
}
I've generated a new project with JHipster v4.6.0 generator and I'm using its EntityMapper interface to do the mapping between domain and DTO objects.
public interface EntityMapper <D, E> {
public E toEntity(D dto);
public D toDto(E entity);
public List <E> toEntity(List<D> dtoList);
public List <D> toDto(List<E> entityList);
}
I need to use the Spring projection to have a smaller domain and DTO objects, (I don't want all fields of the entity), so I've created an interface with only the getters of the fields I need, and I've created a method in the repository which retrive this interface type (following the Spring reference guide)
public interface ClienteIdENome {
Long getId();
String getNome();
}
#Repository
public interface ClienteRepository extends JpaRepository<Cliente,Long> {
ClienteIdENome findById(Long id);
}
The query findById retrieve a ClienteIdENome object with only id and nome fields.
Now, I would like to map this object in the following DTO:
public class ClienteIdENomeDTO implements Serializable {
private static final long serialVersionUID = 1L;
private Long id;
#NotNull
#Size(max = 50)
private String nome;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getNome() {
return nome;
}
public void setNome(String nome) {
this.nome = nome;
}
}
So, I created the mapper interface:
#Mapper(componentModel = "spring", uses = {})
public interface ClienteIdENomeMapper extends EntityMapper<ClienteIdENomeDTO, ClienteIdENome> {
}
But Eclipse report to me an error in the EntityMapper interface for the method "public E toEntity(D dto)" with the message:
No implementation type is registered for return type it.andrea.ztest01.repository.ClienteIdENome.
Any help?
Thanks a lot
Your ClienteIdENome is not really an entity. I would argue that you don't need to use the EntityMapper, but you need to define a one way mapper. From ClienteIdENome to ClienteIdENomeDTO.
Your mapper needs to look like:
public interface ClienteIdENomeMapper {
ClienteIdENomeDTO toDto(ClienteIdENome entity);
List <ClienteIdENomeDTO> toDto(List<ClienteIdENome> entityList);
}
I don't know JHipster, so I can't say what will mean using a mapper different than EntityMapper.
I just start to learn REST and ServiceStack and there's something about Route that I just can't quite understand. For example if we take the very basic HelloWorld example from GitHub tutorial and re-write it to return collection of User objects. Here is example:
public User
{
public string Name;
public string Address;
public int Age;
}
// Hello - request object without [Route] attribute
public class Hello
{
public string Name { get; set; }
}
public class HelloResponse
{
public IEnumerable<User> Result {get;set;}
}
public class HelloService : Service
{
public object Any(Hello request)
{
return new HelloResponse { // Collection of User object };
}
}
now everything working right and no problems here. But now I want to add another routing url like: /Hello/{name}/Address
Actually this call (GET) to this url will return a single User selected by Age parameter. How I can do this ? Should I add another Service ? And if the url will be:
/Hello/{name}/{age}/Address
It seems I don't understand something.....
See this earlier answer for details about Routing in ServiceStack. The Smart Routing section in ServiceStack's New API explains further options and different precedence.
There are a few problems with your example. First ServiceStack text serializers only support public properties so you need to change your User Model to use public properties instead of fields, e.g:
public User
{
public string Name { get; set; }
public string Address { get; set; }
public int Age { get; set; }
}
Next, Interfaces on DTOs are a bad idea as there's no good reason for it. They're still supported but you can end up with undesirable results. Use a concrete collection like a List<T> which provides more utility, e.g:
public class HelloResponse
{
public List<User> Results { get; set; }
}
Also the routes should match the property names on your DTO exactly, they are case-insensitive when matching against the Request Path, but they need to map to an exact property name, e.g:
/Hello/{Name}/{Age}/Address
Here is a sample of what I am trying to accomplish:
public class BaseClass<T>
{
public static T GetByID(int ID)
{
// Need database name here that is determined at design time in the derived class.
var databaseName = "";
// do some stuff involving database name that gets me object by ID here.
return default(T);
}
}
public class DerivedClass : BaseClass<DerivedClass>
{
private string DatabaseName { get; set; }
}
Basically, how would I access the derived "DatabaseName" in the base class static GetByID method?
EDIT: After I posted this, I tried one more thing. I played with attributes earlier, and failed, but I think my brain was mushy. Just tried again and ran a test, and it is working. Here is the updated sample.
public class BaseClass<T>
{
public static T GetByID(int ID)
{
// Need database name here that is determined at design time in the derived class.
var databaseName = ((DatabaseAttribute)typeof(T).GetCustomAttributes(typeof(DatabaseAttribute), true).First()).DatabaseName;
// do some stuff involving database name that gets me object by ID here.
return default(T);
}
}
[Database("MyDatabase")]
public class DerivedClass : BaseClass<DerivedClass>
{
}
public class DatabaseAttribute : Attribute
{
public DatabaseAttribute(string databaseName)
{
DatabaseName = databaseName;
}
public string DatabaseName { get; set; }
}
Base class to derived class is a one-way inheritance: The base class has no knowledge of the existance of a derived class, and so it can't access it.
In addition to that you will have a hard time accessing a non-static property from a static method.
I know you've already answered your own question, but some improvements....
Add a where clause to guarantee inheritance, it means any static methods can make use of inherited methods. You might also want to add the new() clause if you wish to be able to create instances of the inherited class.
public class BaseClass<T> : where T : BaseClass<T>
{
static readonly string databaseName;
static BaseClass() {
// Setup database name once per type of T by putting the initialization in
// the static constructor
databaseName = typeof(T).GetCustomAttributes(typeof(DatabaseAttribute),true)
.OfType<DatabaseAttribute>()
.Select(x => x.Name)
.FirstOrDefault();
}
public static T GetByID(int ID)
{
// Database name will be in the static field databaseName, which is unique
// to each type of T
// do some stuff involving database name that gets me object by ID here.
return default(T);
}
}
[Database("MyDatabase")]
public class DerivedClass : BaseClass<DerivedClass>
{
}
public class DatabaseAttribute : Attribute
{
public DatabaseAttribute(string databaseName)
{
DatabaseName = databaseName;
}
public string DatabaseName { get; set; }
}
I'm writing an app for Java ME, and I need a class for holding some data(PhoneBook). When I'm trying to launch this app, I'm always getting a nullPointerException. I'm calling the constructor of a class, and it allocates memory for 10 elements, so it shouldn't be null. What am I doing wrong?
import javax.microedition.lcdui.*;
import javax.microedition.midlet.MIDlet;
public class TinyMIDlet extends MIDlet implements CommandListener {
private PhoneBook phoneBook = new PhoneBook();
public void initPhoneBook() {
phoneBook.records[0].Name = new String("abc");
}
protected void startApp() {
initPhoneBook();
}
public class Record {
public String Name;
public String Number;
public String email;
public String Group;
}
public class PhoneBook {
public Record[] records;
PhoneBook() {
records = new Record[10];
}
}
}
The array of records isn't null, but each individual element of it is. You need to instantiate each element as well, right now it's just an array with 10 null entries.
phoneBook.records[0].Name = new String("abc");
should be
phoneBook.records[0] = new Record();
phoneBook.records[0].Name= new String("abc");// or = "abc"
I'm not reputable enough yet (heh) to edit Tom's detailed answer, but, to be precise
phoneBook.records[0] = new something();
should be
phoneBook.records[0] = new Record();