HIBERNATE TUTORIAL

HIBERNATE - Hibernate O/R Mapping

<property> element

The <property> element declares a persistent, JavaBean style property of the class.

<property
 

name="propertyName"
column="column_name"
type="typename"
update="true|false"
insert="true|false"
formula="arbitrary SQL expression"
access="field|property|ClassName"
lazy="true|false"
unique="true|false"
not-null="true|false"
optimistic-lock="true|false"

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/> 

All generators implement the interface org.hibernate.id.IdentifierGenerator. This is a very simple interface; some applications may choose to provide their own specialized implementations. However, Hibernate provides a range of built-in implementations. There are shortcut names for the built-in generators:

(1) name: the name of the property, with an initial lowercase letter.
(2) column (optional - defaults to the property name): the name of the mapped database table column. This may also be specified by nested <column> element(s).
(3) type (optional): a name that indicates the Hibernate type.
(4) update, insert (optional - defaults to true) : specifies that the mapped columns should be included in SQL UPDATE and/or INSERT statements. Setting both to false allows a pure "derived" property whose value is initialized from some other property that maps to the same colum(s) or by a trigger or other application.
(5) formula (optional): an SQL expression that defines the value for a computed property. Computed properties do not have a column mapping of their own.
(6) access (optional - defaults to property): The strategy Hibernate should use for accessing the property value.
(7) lazy (optional - defaults to false): Specifies that this property should be fetched lazily when the instance variable is first accessed (requires build-time bytecode instrumentation).
(8) unique (optional): Enable the DDL generation of a unique constraint for the columns. Also, allow this to be the target of a property-ref.
(9) not-null (optional): Enable the DDL generation of a nullability constraint for the columns.
(10) optimistic-lock (optional - defaults to true): Specifies that updates to this property do or do not require acquisition of the optimistic lock. In other words, determines if a version increment should occur when this property is dirty.

typename could be:

  • The name of a Hibernate basic type (eg. integer, string, character, date, timestamp, float, binary, serializable, object, blob).
  • The name of a Java class with a default basic type (eg. int, float, char, java.lang.String, java.util.Date, java.lang.Integer, java.sql.Clob).
  • The name of a serializable Java class.
  • The class name of a custom type (eg. com.illflow.type.MyCustomType).

An especially powerful feature are derived properties. These properties are by definition read-only, the property value is computed at load time. You declare the computation as a SQL expression, this translates to a SELECT clause subquery in the SQL query that loads an instance:

<property name="totalPrice"
formula="( SELECT SUM (li.quantity*p.price) FROM LineItem li, Product p
  WHERE li.productId = p.productId
AND li.customerId = customerId
AND li.orderNumber = orderNumber )"/>


Hibernate tutorial
Introduction to Hibernate
Overview of Hibernate
Features of Hibernate
Getting Started with Hibernate
Hibernate O/R Mapping

Mapping declaration

Mapping Document
<hibernate-mapping> element
<class> element
<id> element
<generator> element
<property> element
<many-to-one> element
<one-to-one> element
Hibernate Mapping In Depth
Hibernate Query Language
Hibernate Complete Example

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