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As an Object/Relational Mapping solution, Hibernate deals with both the Java and JDBC representations of
application data. An online catalog application, for example, most likely has Product
object with a number of attributes such as a sku, name, etc. For these
individual attributes, Hibernate must be able to read the values out of the database and write them back. This
'marshalling' is the function of a Hibernate type, which is an implementation of the
org.hibernate.type.Type interface. In addition, a
Hibernate type describes various aspects of behavior of the Java type such as "how is
equality checked?" or "how are values cloned?".
A Hibernate type is neither a Java type nor a SQL datatype; it provides a information about both.
When you encounter the term type in regards to Hibernate be aware that usage might refer to the Java type, the SQL/JDBC type or the Hibernate type.
Hibernate categorizes types into two high-level groups: value types (see Section 6.1, “Value types”) and entity types (see Section 6.2, “Entity types”).
The main distinguishing characteristic of a value type is the fact that they do not define their own lifecycle. We say that they are "owned" by something else (specifically an entity, as we will see later) which defines their lifecycle. Value types are further classified into 3 sub-categories: basic types (see Section 6.1.1, “Basic value types”), composite types (see Section 6.1.2, “Composite types”) amd collection types (see Section 6.1.3, “Collection types”).
The norm for basic value types is that they map a single database value (column) to a single, non-aggregated Java type. Hibernate provides a number of built-in basic types, which we will present in the following sections by the Java type. Mainly these follow the natural mappings recommended in the JDBC specification. We will later cover how to override these mapping and how to provide and use alternative type mappings.
org.hibernate.type.StringTypeMaps a string to the JDBC VARCHAR type. This is the standard mapping for a string if no Hibernate type is specified.
Registered under string and java.lang.String
in the type registry (see Section 6.5, “Type registry”).
org.hibernate.type.MaterializedClobMaps a string to a JDBC CLOB type
Registered under materialized_clob in the type registry (see
Section 6.5, “Type registry”).
org.hibernate.type.TextTypeMaps a string to a JDBC LONGVARCHAR type
Registered under text in the type registry (see
Section 6.5, “Type registry”).
org.hibernate.type.CharacterType
Maps a char or java.lang.Character to a JDBC CHAR
Registered under char and java.lang.Character in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.BooleanTypeMaps a boolean to a JDBC BIT type
Registered under boolean and java.lang.Boolean in
the type registry (see Section 6.5, “Type registry”).
org.hibernate.type.NumericBooleanTypeMaps a boolean to a JDBC INTEGER type as 0 = false, 1 = true
Registered under numeric_boolean in the type registry (see
Section 6.5, “Type registry”).
org.hibernate.type.YesNoTypeMaps a boolean to a JDBC CHAR type as ('N' | 'n') = false, ( 'Y' | 'y' ) = true
Registered under yes_no in the type registry (see
Section 6.5, “Type registry”).
org.hibernate.type.TrueFalseTypeMaps a boolean to a JDBC CHAR type as ('F' | 'f') = false, ( 'T' | 't' ) = true
Registered under true_false in the type registry (see
Section 6.5, “Type registry”).
org.hibernate.type.ByteType
Maps a byte or java.lang.Byte to a JDBC TINYINT
Registered under byte and java.lang.Byte in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.ShortType
Maps a short or java.lang.Short to a JDBC SMALLINT
Registered under short and java.lang.Short in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.IntegerTypes
Maps an int or java.lang.Integer to a JDBC INTEGER
Registered under int and java.lang.Integerin the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.LongType
Maps a long or java.lang.Long to a JDBC BIGINT
Registered under long and java.lang.Long in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.FloatType
Maps a float or java.lang.Float to a JDBC FLOAT
Registered under float and java.lang.Float in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.DoubleType
Maps a double or java.lang.Double to a JDBC DOUBLE
Registered under double and java.lang.Double in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.BigIntegerType
Maps a java.math.BigInteger to a JDBC NUMERIC
Registered under big_integer and java.math.BigInteger in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.BigDecimalType
Maps a java.math.BigDecimal to a JDBC NUMERIC
Registered under big_decimal and java.math.BigDecimal in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.TimestampType
Maps a java.sql.Timestamp to a JDBC TIMESTAMP
Registered under timestamp, java.sql.Timestamp and
java.util.Date in the type registry (see Section 6.5, “Type registry”).
org.hibernate.type.TimeType
Maps a java.sql.Time to a JDBC TIME
Registered under time and java.sql.Time in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.DateType
Maps a java.sql.Date to a JDBC DATE
Registered under date and java.sql.Date in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.CalendarType
Maps a java.util.Calendar to a JDBC TIMESTAMP
Registered under calendar, java.util.Calendar and
java.util.GregorianCalendar in the type registry (see
Section 6.5, “Type registry”).
org.hibernate.type.CalendarDateType
Maps a java.util.Calendar to a JDBC DATE
Registered under calendar_date in the type registry (see
Section 6.5, “Type registry”).
org.hibernate.type.CurrencyType
Maps a java.util.Currency to a JDBC VARCHAR (using the Currency code)
Registered under currency and java.util.Currency in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.LocaleType
Maps a java.util.Locale to a JDBC VARCHAR (using the Locale code)
Registered under locale and java.util.Locale in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.TimeZoneType
Maps a java.util.TimeZone to a JDBC VARCHAR (using the TimeZone ID)
Registered under timezone and java.util.TimeZone in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.UrlType
Maps a java.net.URL to a JDBC VARCHAR (using the external form)
Registered under url and java.net.URL in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.ClassType
Maps a java.lang.Class to a JDBC VARCHAR (using the Class name)
Registered under class and java.lang.Class in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.BlobType
Maps a java.sql.Blob to a JDBC BLOB
Registered under blob and java.sql.Blob in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.ClobType
Maps a java.sql.Clob to a JDBC CLOB
Registered under clob and java.sql.Clob in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.BinaryTypeMaps a primitive byte[] to a JDBC VARBINARY
Registered under binary and byte[] in the
type registry (see Section 6.5, “Type registry”).
org.hibernate.type.MaterializedBlobTypeMaps a primitive byte[] to a JDBC BLOB
Registered under materialized_blob in the type registry (see
Section 6.5, “Type registry”).
org.hibernate.type.ImageTypeMaps a primitive byte[] to a JDBC LONGVARBINARY
Registered under image in the type registry (see
Section 6.5, “Type registry”).
org.hibernate.type.BinaryTypeMaps a java.lang.Byte[] to a JDBC VARBINARY
Registered under wrapper-binary, Byte[] and
java.lang.Byte[] in the type registry (see Section 6.5, “Type registry”).
org.hibernate.type.CharArrayTypeMaps a char[] to a JDBC VARCHAR
Registered under characters and char[]
in the type registry (see Section 6.5, “Type registry”).
org.hibernate.type.CharacterArrayTypeMaps a java.lang.Character[] to a JDBC VARCHAR
Registered under wrapper-characters, Character[]
and java.lang.Character[] in the type registry (see Section 6.5, “Type registry”).
org.hibernate.type.UUIDBinaryTypeMaps a java.util.UUID to a JDBC BINARY
Registered under uuid-binary and java.util.UUID
in the type registry (see Section 6.5, “Type registry”).
org.hibernate.type.UUIDCharTypeMaps a java.util.UUID to a JDBC CHAR (though VARCHAR is fine too for existing schemas)
Registered under uuid-char in the type registry (see
Section 6.5, “Type registry”).
org.hibernate.type.PostgresUUIDType
Maps a java.util.UUID to the PostgreSQL UUID data type (through
Types#OTHER which is how the PostgreSQL JDBC driver defines it).
Registered under pg-uuid in the type registry (see
Section 6.5, “Type registry”).
org.hibernate.type.SerializableTypeMaps implementors of java.lang.Serializable to a JDBC VARBINARY
Unlike the other value types, there are multiple instances of this type. It
gets registered once under java.io.Serializable.
Additionally it gets registered under the specific
java.io.Serializable implementation class names.
The Java Persistence API calls these embedded types, while Hibernate traditionally called them components. Just be aware that both terms are used and mean the same thing in the scope of discussing Hibernate.
Components represent aggregations of values into a single Java type. For example, you might have an Address class that aggregates street, city, state, etc information or a Name class that aggregates the parts of a person's Name. In many ways a component looks exactly like an entity. They are both (generally speaking) classes written specifically for the application. They both might have references to other application-specific classes, as well as to collections and simple JDK types. As discussed before, the only distinguishing factory is the fact that a component does not own its own lifecycle nor does it define an identifier.
It is critical understand that we mean the collection itself, not its contents. The contents of the collection can in turn be basic, component or entity types (though not collections), but the collection itself is owned.
Collections are covered in Chapter 7, Collection mapping.
The definition of entities is covered in detail in Chapter 4, Persistent Classes. For the purpose of
this discussion, it is enough to say that entities are (generally application-specific) classes which
correlate to rows in a table. Specifically they correlate to the row by means of a unique identifier.
Because of this unique identifier, entities exist independently and define their own lifecycle. As an example,
when we delete a Membership, both the User and
Group entities remain.
This notion of entity independence can be modified by the application developer using the concept of cascades. Cascades allow certain operations to continue (or "cascade") across an association from one entity to another. Cascades are covered in detail in Chapter 8, Association Mappings.
Why do we spend so much time categorizing the various types of types? What is the significance of the distinction?
The main categorization was between entity types and value types. To review we said that entities, by nature of their unique identifier, exist independently of other objects whereas values do not. An application cannot "delete" a Product sku; instead, the sku is removed when the Product itself is deleted (obviously you can update the sku of that Product to null to make it "go away", but even there the access is done through the Product).
Nor can you define an association to that Product sku. You can define an association to Product based on its sku, assuming sku is unique, but that is totally different.
TBC...
Hibernate makes it relatively easy for developers to create their own value types. For
example, you might want to persist properties of type java.lang.BigInteger to
VARCHAR columns. Custom types are not limited to mapping values to a single table
column. So, for example, you might want to concatenate together FIRST_NAME,
INITIAL and SURNAME columns into a java.lang.String.
There are 3 approaches to developing a custom Hibernate type. As a means of illustrating the different
approaches, lets consider a use case where we need to compose a java.math.BigDecimal
and java.util.Currency together into a custom Money class.
The first approach is to directly implement the org.hibernate.type.Type
interface (or one of its derivatives). Probably, you will be more interested in the more specific
org.hibernate.type.BasicType contract which would allow registration of
the type (see Section 6.5, “Type registry”). The benefit of this registration is that whenever
the metadata for a particular property does not specify the Hibernate type to use, Hibernate will
consult the registry for the exposed property type. In our example, the property type would be
Money, which is the key we would use to register our type in the registry:
Example 6.1. Defining and registering the custom Type
public class MoneyType implements BasicType {
public String[] getRegistrationKeys() {
return new String[] { Money.class.getName() };
}
public int[] sqlTypes(Mapping mapping) {
// We will simply use delegation to the standard basic types for BigDecimal and Currency for many of the
// Type methods...
return new int[] {
BigDecimalType.INSTANCE.sqlType(),
CurrencyType.INSTANCE.sqlType(),
};
// we could also have honored any registry overrides via...
//return new int[] {
// mappings.getTypeResolver().basic( BigDecimal.class.getName() ).sqlTypes( mappings )[0],
// mappings.getTypeResolver().basic( Currency.class.getName() ).sqlTypes( mappings )[0]
//};
}
public Class getReturnedClass() {
return Money.class;
}
public Object nullSafeGet(ResultSet rs, String[] names, SessionImplementor session, Object owner) throws SQLException {
assert names.length == 2;
BigDecimal amount = BigDecimalType.INSTANCE.get( names[0] ); // already handles null check
Currency currency = CurrencyType.INSTANCE.get( names[1] ); // already handles null check
return amount == null && currency == null
? null
: new Money( amount, currency );
}
public void nullSafeSet(PreparedStatement st, Object value, int index, boolean[] settable, SessionImplementor session)
throws SQLException {
if ( value == null ) {
BigDecimalType.INSTANCE.set( st, null, index );
CurrencyType.INSTANCE.set( st, null, index+1 );
}
else {
final Money money = (Money) value;
BigDecimalType.INSTANCE.set( st, money.getAmount(), index );
CurrencyType.INSTANCE.set( st, money.getCurrency(), index+1 );
}
}
...
}
Configuration cfg = new Configuration();
cfg.registerTypeOverride( new MoneyType() );
cfg...;
It is important that we registered the type before adding mappings.
Both org.hibernate.usertype.UserType and
org.hibernate.usertype.CompositeUserType were originally
added to isolate user code from internal changes to the org.hibernate.type.Type
interfaces.
The second approach is the use the org.hibernate.usertype.UserType
interface, which presents a somewhat simplified view of the org.hibernate.type.Type
interface. Using a org.hibernate.usertype.UserType, our
Money custom type would look as follows:
Example 6.2. Defining the custom UserType
public class MoneyType implements UserType {
public int[] sqlTypes() {
return new int[] {
BigDecimalType.INSTANCE.sqlType(),
CurrencyType.INSTANCE.sqlType(),
};
}
public Class getReturnedClass() {
return Money.class;
}
public Object nullSafeGet(ResultSet rs, String[] names, Object owner) throws SQLException {
assert names.length == 2;
BigDecimal amount = BigDecimalType.INSTANCE.get( names[0] ); // already handles null check
Currency currency = CurrencyType.INSTANCE.get( names[1] ); // already handles null check
return amount == null && currency == null
? null
: new Money( amount, currency );
}
public void nullSafeSet(PreparedStatement st, Object value, int index) throws SQLException {
if ( value == null ) {
BigDecimalType.INSTANCE.set( st, null, index );
CurrencyType.INSTANCE.set( st, null, index+1 );
}
else {
final Money money = (Money) value;
BigDecimalType.INSTANCE.set( st, money.getAmount(), index );
CurrencyType.INSTANCE.set( st, money.getCurrency(), index+1 );
}
}
...
}
There is not much difference between the org.hibernate.type.Type example
and the org.hibernate.usertype.UserType example, but that is only because
of the snippets shown. If you choose the org.hibernate.type.Type approach
there are quite a few more methods you would need to implement as compared to the
org.hibernate.usertype.UserType.
The third and final approach is the use the org.hibernate.usertype.CompositeUserType
interface, which differs from org.hibernate.usertype.UserType in that it
gives us the ability to provide Hibernate the information to handle the composition within the
Money class (specifically the 2 attributes). This would give us the capability,
for example, to reference the amount attribute in an HQL query. Using a
org.hibernate.usertype.CompositeUserType, our
Money custom type would look as follows:
Example 6.3. Defining the custom CompositeUserType
public class MoneyType implements CompositeUserType {
public String[] getPropertyNames() {
// ORDER IS IMPORTANT! it must match the order the columns are defined in the property mapping
return new String[] { "amount", "currency" };
}
public Type[] getPropertyTypes() {
return new Type[] { BigDecimalType.INSTANCE, CurrencyType.INSTANCE };
}
public Class getReturnedClass() {
return Money.class;
}
public Object getPropertyValue(Object component, int propertyIndex) {
if ( component == null ) {
return null;
}
final Money money = (Money) component;
switch ( propertyIndex ) {
case 0: {
return money.getAmount();
}
case 1: {
return money.getCurrency();
}
default: {
throw new HibernateException( "Invalid property index [" + propertyIndex + "]" );
}
}
}
public void setPropertyValue(Object component, int propertyIndex, Object value) throws HibernateException {
if ( component == null ) {
return;
}
final Money money = (Money) component;
switch ( propertyIndex ) {
case 0: {
money.setAmount( (BigDecimal) value );
break;
}
case 1: {
money.setCurrency( (Currency) value );
break;
}
default: {
throw new HibernateException( "Invalid property index [" + propertyIndex + "]" );
}
}
}
public Object nullSafeGet(ResultSet rs, String[] names, SessionImplementor session, Object owner) throws SQLException {
assert names.length == 2;
BigDecimal amount = BigDecimalType.INSTANCE.get( names[0] ); // already handles null check
Currency currency = CurrencyType.INSTANCE.get( names[1] ); // already handles null check
return amount == null && currency == null
? null
: new Money( amount, currency );
}
public void nullSafeSet(PreparedStatement st, Object value, int index, SessionImplementor session) throws SQLException {
if ( value == null ) {
BigDecimalType.INSTANCE.set( st, null, index );
CurrencyType.INSTANCE.set( st, null, index+1 );
}
else {
final Money money = (Money) value;
BigDecimalType.INSTANCE.set( st, money.getAmount(), index );
CurrencyType.INSTANCE.set( st, money.getCurrency(), index+1 );
}
}
...
}
Internally Hibernate uses a registry of basic types (see Section 6.1.1, “Basic value types”) when
it needs to resolve the specific org.hibernate.type.Type to use in certain
situations. It also provides a way for applications to add extra basic type registrations as well as
override the standard basic type registrations.
To register a new type or to override an existing type registration, applications would make use of the
registerTypeOverride method of the org.hibernate.cfg.Configuration
class when bootstrapping Hibernate. For example, lets say you want Hibernate to use your custom
SuperDuperStringType; during bootstrap you would call:
Example 6.4. Overriding the standard StringType
Configuration cfg = ...;
cfg.registerTypeOverride( new SuperDuperStringType() );
The argument to registerTypeOverride is a org.hibernate.type.BasicType
which is a specialization of the org.hibernate.type.Type we saw before. It
adds a single method:
Example 6.5. Snippet from BasicType.java
/**
* Get the names under which this type should be registered in the type registry.
*
* @return The keys under which to register this type.
*/
public String[] getRegistrationKeys();
One approach is to use inheritance (SuperDuperStringType extends
org.hibernate.type.StringType); another is to use delegation.
Copyright © 2004 Red Hat, Inc.