EORelationship

Inherits from: Object
Implements:
EOPropertyListEncoding
EOSQLExpression.SQLValue

Package: com.webobjects.eoaccess

Class Description

An EORelationship describes an association between two entities, based on attributes of those two entities. By defining EORelationships in your application's EOModel, you can cause the relationships defined in the database to be automatically resolved as enterprise objects are fetched. For example, a Movie entity may contain its studioId as an attribute, but without an EORelationship studioId will only appear in a movie enterprise object as a number. With an EORelationship explicitly connecting the Movie entity to a Studio entity, a movie enterprise object will automatically be given its studio enterprise object when an EODatabaseChannel fetches it from the database. The two entities that make up a relationship can be in the same model or two different models, as long as they are in the same model group.

You usually define relationships in your EOModel with the EOModeler application, which is documented in Enterprise Objects Framework Tools and Techniques. EORelationships are primarily for use by the Enterprise Objects Framework; unless you have special needs you shouldn't need to access them in your application's code. If you have such a need, you can create your own EORelationship objects as outlined in the sections "Creating a Simple Relationship" (page 281) and "Creating a Flattened Relationship" (page 283).

A relationship is directional: One entity is considered the source, and the other is considered the destination. The relationship belongs to the source entity, and may only be traversed from source to destination. To simulate a two-way relationship you have to create an EORelationship for each direction. Although the relationship is directional, no inverse is implied (although an inverse relationship may exist).

A relationship maintains an array of joins identifying attributes from the related entities (see the EOJoin class specification for more information). Most relationships simply relate the objects of one entity to those of another by comparing attribute values between them. Such a relationship must be defined as to-one or to-many based on how many objects of the destination match each object of the source. This is called the cardinality of the relationship. In a to-one relationship, there must be exactly one destination object for each source object; in a to-many relationship there can be any number of destination objects for each source object. See "Creating a Simple Relationship" for more information.

A chain of relationships across several entities can be flattened, creating a single relationship that spans them all. For example, suppose you have a relationship between movies and directors, and a relationship between directors and talent. You can traverse these relationships to create a flattened relationship going directly from movies to talent. A flattened relationship is determined to be to-many or to-one based on the relationships it spans; if all are to-one, then the flattened relationship is to-one, but if any of them is to-many the flattened relationship is to-many. See "Creating a Flattened Relationship" (page 283) for more information.

Like the other major modeling classes, EORelationship provides a user dictionary that the application can use to store application-specific information related to the relationship.

Specifying the Join Semantic

The relationship holds the join semantic; you specify this semantic with setJoinSemantic. There are four types of join semantic : InnerJoin, FullOuterJoin, LeftOuterJoin, and RightOuterJoin. An inner join produces results only for destinations of the join relationship that have non-NULL values. A full outer join produces results for all source records, regardless of the values of the relationships. A left outer join preserves rows in the left (source) table, keeping them even if there's no corresponding row in the right table, while a right outer join preserves rows in the right (destination) table. Note that not all join semantics are supported by all database servers.

Constants

EORelationship defines the following int constants to specify the manner in which a join should be made:

InnerJoin
FullOuterJoin
LeftOuterJoin
RightOuterJoin

Interfaces Implemented

EOPropertyListEncoding
awakeWithPropertyList
encodeIntoPropertyList

Method Types

Constructors
EORelationship

Accessing the relationship name
beautifyName
name
setName

Using joins
addJoin
joins
joinSemantic
removeJoin
setJoinSemantic

Accessing attributes joined on
destinationAttributes
sourceAttributes

Accessing the definition
componentRelationships
definition
setDefinition

Accessing the entities joined
anyInverseRelationship
destinationEntity
entity
inverseRelationship
setEntity

Checking the relationship type
isCompound
isFlattened
isMandatory
setIsMandatory
validateValue

Accessing whether the relationship is to-many
isToMany
setToMany

Relationship qualifiers
qualifierWithSourceRow

Checking references
referencesProperty

Controlling batch fetches
numberOfToManyFaultsToBatchFetch
setNumberOfToManyFaultsToBatchFetch

Taking action upon a change
deleteRule
propagatesPrimaryKey setDeleteRule
setPropagatesPrimaryKey
ownsDestination
setOwnsDestination

Accessing the user dictionary
setUserInfo
userInfo

Constructors

EORelationship

public EORelationship()

Description forthcoming.

public EORelationship( NSDictionary propertyList, EOEntity owner)

Creates and returns a new EORelationship is initialized from propertyList-a dictionary containing only property list data types (that is, NSDictionaries, Strings, NSArrays, and next.util.ImmutableBytes). This constructor is used by EOModeler when it reads in a Model from a file, for example. The owner argument should be the EORelationship's Entity. EORelationships created from a property list must receive an awakeWithPropertyList message immediately after creation before they are fully functional, but the awake... message should be deferred until the all of the other objects in the model have also been created.

See Also: encodeIntoPropertyList (EOPropertyListEncoding interface)

Instance Methods

addJoin

public void addJoin(EOJoin aJoin)

Adds a source-destination attribute pair to the relationship. Throws an exception if the relationship is flattened, if either the source or destination attributes are flattened, or if either of aJoin's attributes already belongs to another join of the relationship.

See Also: joins, isFlattened, setDefinition

anyInverseRelationship

public EORelationship anyInverseRelationship()

Searches the relationship's destination entity for a user-created, back-referencing relationship joining on the same keys. If none is found, it looks for a "hidden" inverse relationship that was manufactured by the Framework. If none is found, the Enterprise Objects Framework creates a "hidden" inverse relationship and returns that. Hidden relationships are used internally by the Framework.

See Also: inverseRelationship

awakeWithPropertyList

public void awakeWithPropertyList(NSDictionary pList)

Description forthcoming.

beautifyName

public void beautifyName()

Makes the relationship's name conform to a standard convention. Names that conform to this style are all lower-case except for the initial letter of each embedded word other than the first, which is upper case. Thus, "NAME" becomes "name", and "FIRST_NAME" becomes "firstName". This method is used in reverse-engineering a model.

See Also: setName, beautifyNames (EOModel)

componentRelationships

public NSArray componentRelationships()

Returns an array of base relationships making up a flattened relationship, or null if the relationship isn't flattened.

See Also: definition

definition

public String definition()

Returns the data path of a flattened relationship; for example "department.facility". If the relationship isn't flattened, definition returns null.

See Also: componentRelationships

deleteRule

public int deleteRule()

Returns a rule that describes the action to take when an object is being deleted. The returned rule is one of the following integers (defined in the control layer's EOClassDescription class):

Value Description

EOClassDescription. DeleteRuleNullify Delete the department and remove any back reference the employee has to the department.

EOClassDescription. DeleteRuleCascade Delete the department and all of the employees it contains.

EOClassDescription. DeleteRuleDeny Refuse the deletion if the department contains employees.

EOClassDescription. DeleteRuleNoAction Delete the department, but ignore the department's employees relationship. You should use this delete rule with caution since it can leave dangling references in your object graph.

destinationAttributes

public NSArray destinationAttributes()

Returns the destination attributes of the relationship. These correspond one-to-one with the attributes returned by sourceAttributes. Returns null if the relationship is flattened.

See Also: joins, destinationAttribute (EOJoin)

destinationEntity

public EOEntity destinationEntity()

Returns the relationship's destination entity, which is determined by the destination entity of its joins for a simple relationship, and by whatever ends the data path for a flattened relationship. For example, if a flattened relationship's definition is "department.facility", the destination entity is the Facility entity.

See Also: entity

encodeIntoPropertyList

public void encodeIntoPropertyList(NSMutableDictionary pList)

Description forthcoming.

entity

public EOEntity entity()

Returns the relationship's source entity.

See Also: destinationEntity, addRelationship (EOEntity)

inverseRelationship

public EORelationship inverseRelationship()

Searches the relationship's destination entity for a user-created, back-referencing relationship joining on the same keys. Returns the inverse relationship if one is found, null otherwise.

See Also: anyInverseRelationship

isCompound

public boolean isCompound()

Returns true if the relationship contains more than one join (that is, if it joins more than one pair of attributes), false if it has only one join. See "Creating a Simple Relationship" (page 281) for information on compound relationships.

See Also: joins, joinSemantic

isFlattened

public boolean isFlattened()

Returns true if the relationship traverses more than two entities, false otherwise. See "Creating a Flattened Relationship" (page 283) for an example of a flattened relationship.

isMandatory

public boolean isMandatory()

Returns true if the target of the relationship is required, false if it can be null.

See Also: setIsMandatory

isToMany

public boolean isToMany()

Returns true if the relationship is to-many, false if it's to-one.

See Also: setToMany

joinSemantic

public int joinSemantic()

Returns the semantic used to create SQL expressions for this relationship. The returned join semantic is one of the following:

Constant Description

InnerJoin Produces results only for destinations of the join relationship that have non-NULL values.

FullOuterJoin Produces results for all source records, regardless of the values of the relationships.

LeftOuterJoin Preserves rows in the left (source) table, keeping them even if there's no corresponding row in the right table.

RightOuterJoin Preserves rows in the right (destination) table, keeping them even if there's no corresponding row in the left table.

See Also: joins

joins

public NSArray joins()

Returns all joins used by relationship.

name

public String name()

Returns the relationship's name.

numberOfToManyFaultsToBatchFetch

public int numberOfToManyFaultsToBatchFetch()

Returns the number of to-many faults that are triggered at one time.

ownsDestination

public boolean ownsDestination()

Returns true if the receiver's source object owns its destination objects, false otherwise. See the method description for setOwnsDestination for more discussion of this topic.

See Also: destinationAttributes

propagatesPrimaryKey

public boolean propagatesPrimaryKey()

Returns true if objects should propagate their primary key to related objects through this relationship. Objects only propagate their primary key values if the corresponding values in the destination object aren't already set.

qualifierWithSourceRow

public com.webobjects.eocontrol.EOQualifier qualifierWithSourceRow( NSDictionary sourceRow)

Returns a qualifier that can be used to fetch the destination of the receiving relationship, given sourceRow.

referencesProperty

public boolean referencesProperty(Object aProperty)

Returns true if aProperty is in the relationship's data path or is an attribute belonging to one of the relationship's joins; otherwise, it returns false. See the class description for information on how relationships reference properties.

See Also: referencesProperty (EOEntity)

relationshipPath

public String relationshipPath()

Description forthcoming.

removeJoin

public void removeJoin(EOJoin aJoin)

Deletes aJoin from the relationship. Does nothing if the relationship is flattened.

See Also: addJoin

setDefinition

public void setDefinition(String definition)

Changes the relationship to a flattened relationship by releasing any joins and attributes (both source and destination) associated with the relationship and setting definition as its data path. "department.facility" is an example of a definition that could be supplied to this method.

If the relationship's entity hasn't been set, this method won't work correctly. See "Creating a Flattened Relationship" (page 283) for more information on flattened relationships.

See Also: addJoin, setEntity

setDeleteRule

public void setDeleteRule(int deleteRule)

Set a rule describing the action to take when object is being deleted. deleteRule can be one of the following (defined in the control layer's EOClassDescription):

EOClassDescription.DeleteRuleNullify
EOClassDescription.DeleteRuleCascade
EOClassDescription.DeleteRuleDeny
EOClassDescription.DeleteRuleNoAction

For more discussion of what these rules mean, see the method description for deleteRule.

setEntity

public void setEntity(EOEntity anEntity)

Sets the entity of the relationship to anEntity. If the relationship is currently owned by a different entity, this method will remove the relationship from that entity. This method doesn't add the relationship to the new entity. EOEntity's addRelationship method invokes this method.

You only need to use this method when creating a flattened relationship; use EOEntity's addRelationship to associate an existing relationship with an entity.

See Also: setDefinition

setIsMandatory

public void setIsMandatory(boolean flag)

Specifies according to flag whether the target of the relationship must be supplied or can be null.

setJoinSemantic

public void setJoinSemantic(int joinSemantic)

Sets the semantic used to create SQL expressions for this relationship. joinSemantic should be one of the following:

InnerJoin
FullOuterJoin
LeftOuterJoin
RightOuterJoin

See Also: addJoin, joinSemantic

setName

public void setName(String name)

Sets the relationship's name to name. Throws a verification exception if name is not a valid relationship name, and an invalid argument exception if name is already in use by an attribute or another relationship in the same entity.

This method forces all objects in the model to be loaded into memory.

See Also: beautifyName

setNumberOfToManyFaultsToBatchFetch

public void setNumberOfToManyFaultsToBatchFetch(int size)

Sets the number of "toMany" faults that are fired at one time to size.

setOwnsDestination

public void setOwnsDestination(boolean flag)

Sets according to flag whether a receiver's source object owns its destination objects. The default is false. When a source object owns its destination objects, it means that the destination objects can't exist independently. For example, in a personnel database, dependents can't exist without having an associated employee. Removing a dependent from an employee's dependents array would have the effect of also deleting the dependent from the database, unless you transferred the dependent to a different employee.

See Also: deleteRule, setDeleteRule, ownsDestination

setPropagatesPrimaryKey

public void setPropagatesPrimaryKey(boolean flag)

Specifies according to flag whether objects should propagate their primary key to related objects through this relationship. For example, an Employee object might propagate its primary key to an EmployeePhoto object. Objects only propagate their primary key values if the corresponding values in the destination object aren't already set.

setToMany

public void setToMany(boolean flag)

Sets a simple relationship as to-many according to flag. Throws an exception if the receiver is flattened. See the class description for considerations in setting this flag.

See Also: isFlattened

setUserInfo

public void setUserInfo(NSDictionary dictionary)

Sets the dictionary of auxiliary data, which your application can use for whatever it needs. dictionary can only contain property list data types (that is, NSDictionary, String, NSArray, and NSData).

sourceAttributes

public NSArray sourceAttributes()

Returns the source attributes of a simple (non-flattened) relationship. These correspond one-to-one with the attributes returned by destinationAttributes. Returns null if the relationship is flattened.

See Also: joins, sourceAttribute (EOJoin)

toString

public String toString()

Returns a String representation of the receiver.

userInfo

public NSDictionary userInfo()

Returns a dictionary of user data. Your application can use this data for whatever it needs.

validateValue

public Object validateValue(Object value) throws NSValidation.ValidationException

For relationships marked as mandatory, throws a validation exception if the receiver is to-one and value is null, or if the receiver is to-many an value has a count of 0. A mandatory relationship is one in which the target of the relationship is required. Returns null to indicate success.

See Also: isMandatory, setIsMandatory

valueForSQLExpression

public String valueForSQLExpression(EOSQLExpression context)

Conformance to EOSQLExpression.SQLValue

Value	Description
`EOClassDescription. DeleteRuleNullify`	Delete the department and remove any back reference the employee has to the department.
`EOClassDescription. DeleteRuleCascade`	Delete the department and all of the employees it contains.
`EOClassDescription. DeleteRuleDeny`	Refuse the deletion if the department contains employees.
`EOClassDescription. DeleteRuleNoAction`	Delete the department, but ignore the department's employees relationship. You should use this delete rule with caution since it can leave dangling references in your object graph.

Constant	Description
`InnerJoin`	Produces results only for destinations of the join relationship that have non-NULL values.
`FullOuterJoin`	Produces results for all source records, regardless of the values of the relationships.
`LeftOuterJoin`	Preserves rows in the left (source) table, keeping them even if there's no corresponding row in the right table.
`RightOuterJoin`	Preserves rows in the right (destination) table, keeping them even if there's no corresponding row in the left table.