Chapter 6. Types

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?".

Important

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”).

6.1. Value 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”).

6.1.1. Basic value 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.

6.1.1.1. java.lang.String

org.hibernate.type.StringType

Maps 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.MaterializedClob

Maps a string to a JDBC CLOB type

Registered under materialized_clob in the type registry (see Section 6.5, “Type registry”).

org.hibernate.type.TextType

Maps a string to a JDBC LONGVARCHAR type

Registered under text in the type registry (see Section 6.5, “Type registry”).

6.1.1.2. `java.lang.Character` (or char primitive)

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”).

6.1.1.3. `java.lang.Boolean` (or boolean primitive)

org.hibernate.type.BooleanType

Maps 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.NumericBooleanType

Maps 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.YesNoType

Maps 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.TrueFalseType

Maps 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.CalendarDateType

Maps a java.util.Calendar to a JDBC DATE

Registered under calendar_date in the type registry (see Section 6.5, “Type registry”).

6.1.1.16. `java.util.Currency`

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”).

6.1.1.17. `java.util.Locale`

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”).

6.1.1.18. `java.util.TimeZone`

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”).

6.1.1.19. `java.net.URL`

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”).

6.1.1.20. `java.lang.Class`

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”).

6.1.1.21. `java.sql.Blob`

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”).

6.1.1.22. `java.sql.Clob`

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”).

6.1.1.23. byte[]

org.hibernate.type.BinaryType

Maps 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.MaterializedBlobType

Maps a primitive byte[] to a JDBC BLOB

Registered under materialized_blob in the type registry (see Section 6.5, “Type registry”).

org.hibernate.type.ImageType

Maps a primitive byte[] to a JDBC LONGVARBINARY

Registered under image in the type registry (see Section 6.5, “Type registry”).

6.1.1.24. Byte[]

org.hibernate.type.BinaryType

Maps 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”).

6.1.1.25. char[]

org.hibernate.type.CharArrayType

Maps a char[] to a JDBC VARCHAR

Registered under characters and char[] in the type registry (see Section 6.5, “Type registry”).

6.1.1.26. Character[]

org.hibernate.type.CharacterArrayType

Maps 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”).

6.1.1.27. `java.util.UUID`

org.hibernate.type.UUIDBinaryType

Maps 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.UUIDCharType

Maps 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”).

6.1.1.28. `java.io.Serializable`

org.hibernate.type.SerializableType

Maps 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.

6.1.2. Composite types

Note

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.

6.1.3. Collection types

Important

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.

6.2. Entity types

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.

Note

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.

6.3. Significance of type categories

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...

6.4. Custom types

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.

6.4.1. Custom types using `org.hibernate.type.Type`

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...;

Important

It is important that we registered the type before adding mappings.

6.4.2. Custom types using `org.hibernate.usertype.UserType`

Note

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.

6.4.3. Custom types using `org.hibernate.usertype.CompositeUserType`

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 );

        }

    }


    ...

}

6.5. Type registry

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.