one-to-one

This is my Database structure, One-to-One mapping in MySQL: This is my java file: public class Employee { private EmployeeDetail empdetail; private String firstname; private String lastname; // getters and setters } public class EmployeeDetail { private Employee employee ; private int employee_id; private String street; private String city; private String state; private String country; // getters and setters } This is my mapping file: <hibernate-mapping> <class name="Employee" table="employee"> <id name="employee_id" type="java.lang.Integer" column="employee_id"> <generator class="assigned" />

I have User and Address classes as follows: class User { ... ... @OneToOne( cascade=CascadeType.ALL) @JoinColumn(name="addr_id") private Address address; } class Address { ... ... @OneToOne(mappedBy="address") private User user; } Here my assumption is with this domain model I can associate one address to only one user(user.addr_id should be unique). But with this domain model, I am able to create multiple users and associate them to the same address. User u1 = new User(); //set data Address addr1 = new Address(); //set data u1.setAddress(addr1); ... session.save(u1); --> this is creating one

i have entity A that has-a B entity, and B has-a A with @OneToOne bidirectional association. Now, when i findall A records, hibernate perform two queries with a left outer join on B, something like this: select a.id, a.id_b, a.field1, b.id, b.field1 from A as a, B as b left outer join b ON b.id=a.id_b; select a.id, a.id_b, a.field1, b.id, b.field1 from A as a, B as b left outer join b ON b.id=a.id_b WHERE b.id=? First query load A and B fields and it is ok, but why perform second query to reload A? I think this query load the A content in B, but this A is obviusly the A that contains B... so

I'm trying to achieve One To One relation in MySQL database. For example, let's say I have Users table and Accounts table. And I want to be sure there is User can have only one account. And that there can be only one Account per user. I found two solutions for this but don't know what to use, and are there any other options. First solution: DROP DATABASE IF EXISTS test; CREATE DATABASE test CHARSET = utf8 COLLATE = utf8_general_ci; USE test; CREATE TABLE users( id INT NOT NULL AUTO_INCREMENT, user_name VARCHAR(45) NOT NULL, PRIMARY KEY(id) ) ENGINE = InnoDB DEFAULT CHARSET = utf8; CREATE TABLE

I'm having a little difficulty getting my head around relationships in Django models. Could someone explain what the difference is between a OneToOne, ManyToMany and ForeignKey? Well, there's essentially two questions here: What is the difference (in general) between one to one, many to many, and foreign key relations What are their differences specific to Django. Both of these questions are quite easily answered through a simple Google search, but as I cannot find an exact dupe of this question on SO, I'll go ahead and answer. Note that in Django, relationships should only be defined on one

I have this two entities: public partial class Ficheros { public Guid Idfichero { get; set; } public long Iddocumento { get; set; } public byte[] Fichero { get; set; } public virtual Documentos IddocumentoNavigation { get; set; } } public partial class Documentos { public Documentos() { ElementosDocumentos = new HashSet<ElementosDocumentos>(); } public long Iddocumento { get; set; } public string Nombre { get; set; } public long? IdtipoDocumento { get; set; } public string Codigo { get; set; } public decimal? Espacio { get; set; } public string Unidades { get; set; } public long? Bytes { get;