5.2.2.1. Metadata Interfaces

Let’s consider the basic metadata interfaces.

MetadataFramework
Figure 9. Metadata Framework Interfaces
Session

Entry point of the metadata framework. Enables obtaining MetaClass instances by name and by the corresponding Java class. Note the difference in methods: getClass() methods can return null while getClassNN() (Non Null) methods cannot.

Session object can be obtained using the Metadata infrastructure interface.

Example:

@Inject
protected Metadata metadata;
...
Session session = metadata.getSession();
MetaClass metaClass1 = session.getClassNN("sec$User");
MetaClass metaClass2 = session.getClassNN(User.class);
assert metaClass1 == metaClass2;
MetaModel

Rarely used interface intended to group meta-classes.

Meta-classes are grouped by the root name of Java project package specified in metadata.xml file.

MetaClass

Entity class metadata interface. MetaClass is always associated with the Java class which it represents.

Basic methods:

  • getName() – entity name, according to convention the first part of the name before $ sign is the namespace code, for example, sales$Customer.

  • getProperties() – the list of meta-properties (MetaProperty).

  • getProperty(), getPropertyNN() – methods return meta-properties by name. If there is no attribute with provided name, the first method returns null, and the second throws an exception.

    Example:

    MetaClass userClass = session.getClassNN(User.class);
MetaProperty groupProperty = userClass.getPropertyNN("group");

  • getPropertyPath() – allows you to navigate by references. This method accepts string parameter – path in the format of dot-separated attribute names. The returned MetaPropertyPath object enables accessing the required (the last in the path) attribute by invoking getMetaProperty() method.

    Example:

    MetaClass userClass = session.getClassNN(User.class);
MetaProperty groupNameProp = userClass.getPropertyPath("group.name").getMetaProperty();
assert groupNameProp.getDomain().getName().equals("sec$Group");

  • getJavaClass() – entity class, corresponding to this MetaClass.

  • getAnnotations() – collection of meta-annotations.

MetaProperty

Entity attribute metadata interface.

Basic methods:

  • getName() – property name, corresponds to entity attribute name.

  • getDomain() – meta-class, owning this property.

  • getType()- the property type:

    • simple type: DATATYPE

    • enumeration: ENUM

    • reference type of two kinds:

      • ASSOCIATION − simple reference to another entity. For example, Order-Customer relationship is an association.

      • COMPOSITION − reference to the entity, having no consistent value without the owning entity. COMPOSITION is considered to be a "closer" relationship than ASSOCIATION. For example, the relationship between Order and its Items is a COMPOSITION, as the Item cannot exist without the Order to which it belongs.

        The type of ASSOCIATION or COMPOSITION reference attributes affects entity edit mode: in the first case the related entity is persisted to the database independently, in the second case – only together with the owning entity. See Composite Structures for details.

  • getRange() – Range interface providing detailed description of the attribute type.

  • isMandatory() – indicates a mandatory attribute. For instance, it is used by visual components to signal a user that value is mandatory.

  • isReadOnly() – indicates a read-only attribute.

  • getInverse() – for reference-type attribute, returns the meta-property from the other side of the association, if such exists.

  • getAnnotatedElement() – field (java.lang.reflect.Field) or method (java.lang.reflect.Method), corresponding to the entity attribute.

  • getJavaType() – Java class of the entity attribute. It can either be the type of corresponding field or the type of the value returned by corresponding method.

  • getDeclaringClass() – Java class containing this attribute.

    Range

    Interface describing entity attribute type in detail.

    Basic methods:

  • isDatatype() – returns true for simple type attribute.

  • asDatatype() – returns Datatype for simple type attribute.

  • isEnum() – returns true for enumeration type attribute.

  • asEnumeration() – returns Enumeration for enumeration type attribute.

  • isClass() – returns true for reference attribute of ASSOCIATION or COMPOSITION type.

  • asClass() – returns metaclass of associated entity for a reference attribute.

  • isOrdered() – returns true if the attribute is represented by an ordered collection (for example List).

  • getCardinality() – relation kind of the reference attribute: ONE_TO_ONE, MANY_TO_ONE, ONE_TO_MANY, MANY_TO_MANY.