13_metamodel.adoc

Metamodel

The metamodel for entity views is very similar to the JPA metamodel and the entry point is ViewMetamodel which can be acquired through EntityViewManager.getMetamodel()

It allows access to views(ViewType) and flat views(FlatViewType) which both are subtypes of managed views(ManagedViewType). The only difference between the two is that a flat view has no id mapping, so it’s identity is composed of all attributes which results in some limitations as described in the flat view mapping section.

interface ManagedViewType {
    +getJavaType()
    +getEntityClass()
    +getAttributes()
    +getAttribute(String name)
    +getDefaultBatchSize()
    +getConstructors()
    +getConstructor(Class<?>... paramTypes)
    +getConstructorNames()
    +getConstructor(String name)
}
interface ViewType {
    +getName()
    +getIdAttribute()
    +isUpdatable()
    +isPartiallyUpdatable()
    +getViewFilter(String name)
    +getViewFilters()
}
interface FlatViewType {
}
interface MappingConstructor {
    +getName()
    +getDeclaringType()
    +getJavaConstructor()
    +getParameterAttributes()
    +getParameterAttribute(int index)
}
interface FilterMapping {
    +getName()
    +isViewFilter()
    +getFilterClass()
}
interface ViewFilterMapping {
    +getDeclaringType()
}
ManagedViewType <|-- ViewType
ManagedViewType <|-- FlatViewType
FilterMapping <|-- ViewFilterMapping

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A view can have multiple named constructors that have parameter attributes. Additionally, a view can also have multiple named view filters. Every managed view has attributes which are structured based on the arity(singular or plural), the mapping type(parameter or method) and correlation type(normal, subquery or correlated).

interface Attribute {
    +getDeclaringType()
    +getJavaType()
    +isSubquery()
    +isCollection()
    +isSubview()
    +isCorrelated()
    +getFetchStrategy()
    +getBatchSize()
}

interface SingularAttribute {
    +isQueryParameter()
    +isId()
}

interface PluralAttribute {
    +getCollectionType()
    +getElementType()
    +isIndexed()
    +isOrdered()
    +isSorted()
    +getComparator()
    +getComparatorClass()
}

interface MethodAttribute {
    +getName()
    +isUpdatable()
    +getJavaMethod()
    +getFilter(String filterName)
    +getFilters()
}
interface ParameterAttribute {
    +getIndex()
    +getDeclaringConstructor()
}

interface MappingAttribute {
    +getMapping()
}
interface CorrelatedAttribute {
    +getCorrelationProvider()
    +getCorrelationBasis()
    +getCorrelationResult()
}
interface SubqueryAttribute {
    +getSubqueryProvider()
    +getSubqueryExpression()
    +getSubqueryAlias()
}

enum CollectionType {
    COLLECTION
    LIST
    MAP
    SET
}

interface CollectionAttribute
interface SetAttribute
interface ListAttribute
interface MapAttribute {
    +getKeyType()
    +isKeySubview()
}

interface FilterMapping {
    +getName()
    +isViewFilter()
    +getFilterClass()
}
interface AttributeFilterMapping {
    +getDeclaringAttribute()
}


Attribute <|-- SingularAttribute
Attribute <|-- PluralAttribute

Attribute <|-- MethodAttribute
Attribute <|-- ParameterAttribute

Attribute <|-- MappingAttribute
Attribute <|-- CorrelatedAttribute
SingularAttribute <|-- SubqueryAttribute

PluralAttribute <|-- ListAttribute
PluralAttribute <|-- MapAttribute
PluralAttribute <|-- CollectionAttribute
PluralAttribute <|-- SetAttribute

FilterMapping <|-- AttributeFilterMapping

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show CollectionType fields
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An attribute is always either an instance of ParameterAttribute or MethodAttribute depending on whether it is defined on a constructor as parameter or as getter method. A parameter attribute is defined by it’s index and it’s declaring MappingConstructor. Method attributes have a name, may have multiple named attribute filters and might possibly be updatable.

A singular attribute is always an instance of SingularAttribute and is given if isCollection() returns false. If it is a subquery i.e. isSubquery() returns true, it is also an instance of SubqueryAttribute. If it is correlated i.e. isCorrelated() returns true, it is also an instance of CorrelatedAttribute. If it is neither a subquery nor correlated, it is going to be an instance of MappingAttribute.

A plural attribute is always an instance of PluralAttribute and is given if isCollection() return true. Since plural attributes can’t be defined via a subquery mapping, it is never an instance of SubqueryAttribute. If it is correlated i.e. isCorrelated() returns true, it is also an instance of CorrelatedAttribute, otherwise it is going to be an instance of MappingAttribute. Depending on the collection type returned by getCollectionType a plural attribute is also an instance of

• CollectionAttribute if CollectionType.COLLECTION

• ListAttribute if CollectionType.LIST

• SetAttribute if CollectionType.SET

• MapAttribute if CollectionType.MAP