EORelationship

Inherits From:
NSObject

Conforms To: NSObject (NSObject)

Declared in: EOAccess/EORelationship.h

You usually define relationships in your EOModel with the EOModeler application, which is documented in WebObjects 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 "Creating Relationships."

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" 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.

Note: Not all join semantics are supported by all database servers.

Adopted Protocols

EOPropertyListEncoding

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- awakeWithPropertyList

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- encodeIntoPropertyList:

- initWithPropertyList:owner:

Accessing the relationship name - beautifyName

- name

- setName:

- validateName:

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

addJoin:

Adds a source-destination attribute pair to the relationship. Raises an NSInvalidArgumentException 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

Searches the relationship's destination entity for a user-created, back-pointing 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

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:, - validateName:, - beautifyNames (EOModel)

componentRelationships

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

See also: - definition

definition

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

See also: - componentRelationships

deleteRule

Returns a rule that describes the action to take when an object is being deleted. The returned rule is one of the following:

Value	Type	Description
EODeleteRuleNullify	int	Delete the department and remove any back pointer the employee has to the department.
EODeleteRuleCascade	int	Delete the department and all of the employees it contains.
EODeleteRuleDeny	int	Refuse the deletion if the department contains employees.
EODeleteRuleNoAction	int	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

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

See also: - joins, - destinationAttribute (EOJoin)

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

entity

Returns the relationship's source entity.

See also: - destinationEntity, - addRelationship: (EOEntity)

inverseRelationship

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

See also: - anyInverseRelationship

isCompound

Returns YES if the relationship contains more than one join (that is, if it joins more than one pair of attributes), NO if it has only one join. See "Creating a Simple Relationship" for information on compound relationships.

See also: - joins, - joinSemantic

isFlattened

Returns YES if the relationship traverses more than two entities, NO otherwise. See "Creating a Flattened Relationship" for an example of a flattened relationship.

isMandatory

Returns YES if the target of the relationship is required, NO if it can be nil.

See also: - setIsMandatory:

isToMany

Returns YES if the relationship is to-many, NO if it's to-one.

See also: - setToMany:

joinSemantic

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

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

See also: - joins

joins

Returns all joins used by relationship.

See also: - destinationAttributes, - joinSemantic, - sourceAttributes

name

Returns the relationship's name.

numberOfToManyFaultsToBatchFetch

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

ownsDestination

Returns YES if the receiver's source object owns its destination objects, NO otherwise. See the method description for setOwnsDestination: for more discussion of this topic.

See also: - destinationAttributes

propagatesPrimaryKey

Returns YES 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:

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

referencesProperty:

Returns YES if aProperty is in the relationship's data path or is an attribute belonging to one of the relationship's joins; otherwise, it returns NO. See the class description for information on how relationships reference properties.

See also: - referencesProperty: (EOEntity)

removeJoin:

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

See also: - addJoin:

setDefinition:

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" for more information on flattened relationships.

See also: - addJoin:, - setEntity:

setDeleteRule:

Set a rule describing the action to take when object is being deleted. deleteRule can be one of the following:

• EODeleteRuleNullify
• EODeleteRuleCascade
• EODeleteRuleDeny
• EODeleteRuleNoAction

setEntity:

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:

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

setJoinSemantic:

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

• EOInnerJoin
• EOFullOuterJoin
• EOLeftOuterJoin
• EORightOuterJoin

setName:

Sets the relationship's name to name. Raises a verification exception if name is not a valid relationship name, and NSInvalidArgumentException 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, - validateName:

setNumberOfToManyFaultsToBatchFetch:

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

See also: - isToMany, - numberOfToManyFaultsToBatchFetch

setOwnsDestination:

Sets according to flag whether a receiver's source object owns its destination objects. The default is NO. 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:

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:

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

See also: - isFlattened

setUserInfo:

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, NSString, NSArray, and NSData).

sourceAttributes

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

See also: - joins, - sourceAttribute (EOJoin)

userInfo

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

validateName:

Validates name and returns nil if its a valid name, or an exception if it isn't. A name is invalid if it has zero length; starts with a character other than a letter, a number, or "@", "#", or "_"; or contains a character other than a letter, a number, "@", "#", "_", or "$". A name is also invalid if the receiver's EOEntity already has an EORelationship with the same name, or if the model has a stored procedure that has an argument with the same name.

setName: uses this method to validate its argument.

validateValue:

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

See also: - isMandatory, - setIsMandatory: