2d barcode vb.net The UserAccount Entity Bean with Hibernate Annotations in Java

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Listing 4-11. The UserAccount Entity Bean with Hibernate Annotations
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package com.apress.timesheets.entity; import import import import static javax.persistence.CascadeType.PERSIST; static javax.persistence.FetchType.LAZY; java.util.*; javax.persistence.*;
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@Entity @NamedQueries( { @NamedQuery(name query = @NamedQuery(name query = })
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= "getUserAccountByName", "from UserAccount where accountName = :name"), = "listUserAccountByName", "from UserAccount order by accountName")
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CHAPTER 4 DATA ACCESS
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public class UserAccount { private Long id; private String accountName; private Set<UserRole> roles = new HashSet<UserRole>(); public UserAccount() { } public UserAccount(final String accountName) { this.accountName = accountName; } @Id @GeneratedValue public Long getId() { return id; } public void setId(final Long id) { this.id = id; } @ManyToMany(fetch = LAZY, cascade = PERSIST) @JoinTable(name = "account_role", joinColumns = { @JoinColumn(name = "user") }, inverseJoinColumns = { @JoinColumn(name = "role") }) public Set<UserRole> getRoles() { return roles; } public void setRoles(final Set<UserRole> roles) { this.roles = roles; } @Column(unique = true, nullable = false) public String getAccountName() { return accountName; } public void setAccountName(String accountName) { this.accountName = accountName; } }
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There are two types of annotations available to Hibernate. For the basic mapping information, Hibernate takes advantage of standard JPA annotations in the javax.persistence package namespace. A Hibernate entity mapped exclusively by using these annotations can be supported by other JPA-compliant ORM tools. Hibernate also offers a set of Hibernatespecific annotations that can be used to enable additional Hibernate features. Although we are using a Hibernate-specific set of Spring implementation classes, my implementation does not require any Hibernate-specific annotations.
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The @Entity Annotation
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The @Entity annotation marks the class as being an entity for persistence into the database. Optionally, the annotation can supply the default name for the table that the entity will be mapped to.
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The @Id Annotation
The @Id annotation marks the property as representing the primary key of the entity. Although I am using a surrogate key that will be generated automatically (see @GeneratedValue), there is nothing to prevent you from assigning one of your business attributes as the primary key field, and if you need to use multiple attributes, additional annotations are available to support this.
The @GeneratedValue Annotation
The @GeneratedValue annotation is used here to indicate that the primary key (Id) attribute that it is attached to will be generated by Hibernate rather than being explicitly assigned. This reduces the burden on the developer quite considerably. Because I have not specified any further details, the generated value will be created in the default manner for the underlying database, allowing you to take advantage of database-specific features without creating a dependency on the specific database in your implementation. This usage does, however, require you to create an appropriate set of database objects to support Hibernate. In the case of HSQLDB, which I use in my example configuration, this entails the use of an identity type on the primary key column.
The @Column Annotation
The @Column annotation can be used to specify a column name (other than the default of the attribute name), or as here can be used to indicate that additional constraints should apply to the column. I have specified that the accountName attribute is unique, and that it should not accept a null value.
The @ManyToMany Annotation
The @ManyToMany annotation indicates the relationship between the two entities. Any UserAccount may be associated with any UserRole entity and vice versa. The fetch type of
CHAPTER 4 DATA ACCESS
LAZY indicates that a UserRole entity will not be loaded immediately (see the Hibernate Lazy Loading section later in this chapter). The cascade type indicates that when we save the UserAccount entity, any unsaved UserRole entities associated with it should be saved too.
The @JoinTable Annotation
The @JoinTable annotation supplements the @ManyToMany annotation. It is impossible to express a many-to-many relationship between two database entities by using a simple foreign key relationship in the relevant tables. Instead, a join table must be created to manage the relationship. Here we specify the name of the join table as account_role, and the name of the columns of the table. These will be foreign keys into the UserAccount (joinColumns) and UserRole (inverseJoinColumns) tables, respectively.
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