转：HIBERNATE - Hibernate Mapping In Depth

HIBERNATE TUTORIAL

HIBERNATE - Hibernate Mapping In Depth

Hibernate allows the mapping of Mapped tables with the domain objects using the persistent collection-valued fields. These fields needs be declared as an interface type. The actual interface can be java.util.Set, java.util.Collection, java.util.List, java.util.Map, java.util.SortedSet, java.util.SortedMap or custom implementations of org.hibernate.usertype.UserCollectionType

Collections instances have the usual behavior of value types. They are automatically persisted when referenced by a persistent object and automatically deleted when unreferenced. If a collection is passed from one persistent object to another, its elements might be moved from one table to another. Two entities may not share a reference to the same collection instance. Due to the underlying relational model, collection-valued properties do not support null value semantics;

public class Product {
	private String serialNumber; private Set parts = new HashSet(); public Set getParts() { return parts; } void setParts(Set parts) { this.parts = parts; } public String getSerialNumber() { return serialNumber; } void setSerialNumber(String sn) { serialNumber = sn; }
}

Collection Mapping

<map
	name="propertyName" table="table_name" schema="schema_name" lazy="true|false" inverse="true|false" cascade="all|none|save-update|delete|all-delete-orphan" sort="unsorted|natural|comparatorClass" order-by="column_name asc|desc" where="arbitrary sql where condition" fetch="join|select" batch-size="N" access="field|property|ClassName" optimistic-lock="true|false" > <key .... /> <map-key .... /> <element .... />		(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)
</map>

(1)	name the collection property name
(2)	table (optional - defaults to property name) the name of the collection table (not used for one-to-many associations)
(3)	schema (optional) the name of a table schema to override the schema declared on the root element
(4)	lazy (optional - defaults to true) enable lazy initialization (not available for arrays)
(5)	inverse (optional - defaults to false) mark this collection as the "inverse" end of a bidirectional association
(6)	cascade (optional - defaults to none) enable operations to cascade to child entities
(7)	sort (optional) specify a sorted collection with natural sort order, or a given comparator class
(8)	order-by (optional, JDK1.4 only) specify a table column (or columns) that define the iteration order of the Map, Set or bag, together with an optional asc or desc
(9)	where (optional) specify an arbitrary SQL WHERE condition to be used when retrieving or removing the collection (useful if the collection should contain only a subset of the available data)
(10)	fetch (optional, defaults to select) Choose between outer-join fetching and fetching by sequential select. Only one collection may be fetched by outer join per SQL SELECT.
(11)	batch-size (optional, defaults to 1) specify a "batch size" for lazily fetching instances of this collection.
(12)	access (optional - defaults to property): The strategy Hibernate should use for accessing the property value.
(13)	optimistic-lock (optional - defaults to true): Species that changes to the state of the collection results in increment of the owning entity's version. (For one to many associations, it is often reasonable to disable this setting.)

These are some more mapings which we will discuss later

Association Mapping
Component Mapping
Instance Mapping