com.erudika.para.core

Class Linker

java.lang.Object

com.erudika.para.core.Linker

All Implemented Interfaces:

Linkable, ParaObject, Votable, Serializable

public final class Linker
extends Object
implements ParaObject, Serializable

This class represents a many-to-many relationship (link) between two objects.

Author:

Alex Bogdanovski [alex@erudika.com]

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface com.erudika.para.core.Votable

Votable.VoteValue

Constructor Summary

Constructors

Constructor and Description
Linker() No-args constructor.
Linker(String type1, String type2, String id1, String id2) A link.

Method Summary

Modifier and Type	Method and Description
void	addNestedObject(ParaObject obj) Add an object to nest inside the linker object.
Long	countChildren(String type) Count the total number of child objects for this object.
Long	countLinks(String type2) Count the total number of links between this object and another type of object.
String	create() Stores this object in the data store.
void	delete() Deletes the object permanently by removing it from the data store.
void	deleteChildren(String type) Deletes all child objects permanently.
boolean	equals(Object obj)
boolean	exists() Checks if an object is stored in the data store.
<P extends ParaObject> List<P>	findChildren(String type, String query, Pager... pager) Search through all child objects.
<P extends ParaObject> List<P>	findLinkedObjects(String type, String field, String query, Pager... pager) Similar to Linkable.findChildren(java.lang.String, java.lang.String, com.erudika.para.utils.Pager...) but for many-to-many relationships.
String	getAppid() The application name.
Boolean	getCached() Boolean flag which controls whether this object is cached.
<P extends ParaObject> List<P>	getChildren(String type, Pager... pager) Returns all child objects linked to this object.
<P extends ParaObject> List<P>	getChildren(String type, String field, String term, Pager... pager) Returns all child objects linked to this object.
String	getCreatorid() The id of the user who created this.
String	getId() The id of an object.
String	getId1() Returns the id of the first object in the link.
String	getId2() Returns the id of the second object in the link.
String	getIdFieldNameFor(String type) Returns "id1" or "id2" depending on the alphabetical order of type.
Boolean	getIndexed() Boolean flag which controls whether this object is indexed by the search engine.
<P extends ParaObject> List<P>	getLinkedObjects(String type, Pager... pager) Similar to Linkable.getChildren(java.lang.String, com.erudika.para.utils.Pager...) but for many-to-many relationships.
List<Linker>	getLinks(String type2, Pager... pager) Returns all links between this type object and another type of object.
String	getMetadata() Returns the additional information about the link.
String	getName() The name of the object.
List<Map<String,Object>>	getNstd() Get the nested objects that are linked by this link.
String	getObjectURI() The URI of this object.
String	getParentid() The id of the parent object.
String	getPlural() The plural name of the object.
Boolean	getStored() Boolean flag which controls whether this object is stored in the database or not.
List<String>	getTags() The tags associated with this object.
Long	getTimestamp() The time when the object was created, in milliseconds.
String	getType() The name of the object's class.
String	getType1() Returns the type of the first object in the link.
String	getType2() Returns the type of the second object in the link.
Long	getUpdated() The last time this object was updated.
Long	getVersion() Returns the version number for this object.
Integer	getVotes() Returns the total sum of all votes for this object.
int	hashCode()
boolean	isFirst(String type2) Checks if the position of a given object is first or second.
boolean	isLinked(ParaObject toObj) Checks if a given object is linked to this one.
boolean	isLinked(String type2, String id2) Checks if this object is linked to another.
String	link(String id2) Links an object to this one in a many-to-many relationship.
void	setAppid(String appid) Sets a new app name.
void	setCached(Boolean cached) Sets the "isCached" flag.
void	setCreatorid(String creatorid) Sets a new creator id.
void	setId(String id) Sets a new id.
void	setId1(String id1) Sets the id of the first object in the link.
void	setId2(String id2) Sets the id of the second object in the link.
void	setIndexed(Boolean indexed) Sets the "isIndexed" flag.
void	setMetadata(String metadata) Sets additional information about the link.
void	setName(String name) Sets a new name.
void	setNstd(List<Map<String,Object>> nstd) Sets the nested array of objects that are linked by this link.
void	setParentid(String parentid) Sets a new parent id.
void	setStored(Boolean stored) Sets the "isStored" flag.
void	setTags(List<String> tags) Merges the given tags with existing tags.
void	setTimestamp(Long timestamp) Sets the timestamp.
void	setType(String type) Sets a new object type.
void	setType1(String type1) Sets the type of the first object in the link.
void	setType2(String type2) Sets the type of the second object in the link.
void	setUpdated(Long updated) Sets the last updated timestamp.
void	setVersion(Long version) Sets the version of this object.
void	setVotes(Integer votes) Sets the total votes for this object.
String	toString()
void	unlink(String type, String id2) Unlinks an object from this one.
void	unlinkAll() Unlinks all objects that are linked to this one.
void	update() Updates the object permanently.
boolean	voteDown(String userid) Downvotes the object.
boolean	voteUp(String userid) Upvotes the object.

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

Linker

public Linker()

No-args constructor.

Linker

public Linker(String type1,
              String type2,
              String id1,
              String id2)

A link. The names of the objects are compared and sorted alphabetically.

Parameters:

type1 - the type of the first object

type2 - the type of the second object

id1 - the id of the first object

id2 - the id of the second object

Method Detail

getId2

public String getId2()

Returns the id of the second object in the link.

Returns:

the id

setId2

public void setId2(String id2)

Sets the id of the second object in the link.

Parameters:

id2 - a new id

getId1

public String getId1()

Returns the id of the first object in the link.

Returns:

the id

setId1

public void setId1(String id1)

Sets the id of the first object in the link.

Parameters:

id1 - a new id

getType1

public String getType1()

Returns the type of the first object in the link.

Returns:

the type

setType1

public void setType1(String type1)

Sets the type of the first object in the link.

Parameters:

type1 - the type

getType2

public String getType2()

Returns the type of the second object in the link.

Returns:

the type

setType2

public void setType2(String type2)

Sets the type of the second object in the link.

Parameters:

type2 - second type

getMetadata

public String getMetadata()

Returns the additional information about the link.

Returns:

some info

setMetadata

public void setMetadata(String metadata)

Sets additional information about the link.

Parameters:

metadata - some info

isFirst

public boolean isFirst(String type2)

Checks if the position of a given object is first or second.

Parameters:

type2 - the given class of object

Returns:

true if the object's type is equal to getType1()

getIdFieldNameFor

public String getIdFieldNameFor(String type)

Returns "id1" or "id2" depending on the alphabetical order of type.

Parameters:

type - the type

Returns:

id1 or id2

getNstd

public List<Map<String,Object>> getNstd()

Get the nested objects that are linked by this link.

Returns:

a 2-element array of objects or null

setNstd

public void setNstd(List<Map<String,Object>> nstd)

Sets the nested array of objects that are linked by this link.

Parameters:

nstd - an array of 2 objects only

addNestedObject

public void addNestedObject(ParaObject obj)

Add an object to nest inside the linker object. Used for joining queries when searching objects in a many-to-many relationship.

Parameters:

obj - object

getId

public String getId()

Description copied from interface: ParaObject

The id of an object. Usually an autogenerated unique string of numbers.

Specified by:

getId in interface ParaObject

Returns:

the id

setId

public void setId(String id)

Description copied from interface: ParaObject

Sets a new id. Must not be null or empty.

Specified by:

setId in interface ParaObject

Parameters:

id - the new id

getType

public String getType()

Description copied from interface: ParaObject

The name of the object's class. This is equivalent to Class.getSimpleName().toLowerCase()

Specified by:

getType in interface ParaObject

Returns:

the simple name of the class

setType

public void setType(String type)

Description copied from interface: ParaObject

Sets a new object type. Must not be null or empty.

Specified by:

setType in interface ParaObject

Parameters:

type - a new type

getAppid

public String getAppid()

Description copied from interface: ParaObject

The application name. Added to support multiple separate apps. Every object must belong to an app.

Specified by:

getAppid in interface ParaObject

Returns:

the app id (name). default: para

setAppid

public void setAppid(String appid)

Description copied from interface: ParaObject

Sets a new app name. Must not be null or empty.

Specified by:

setAppid in interface ParaObject

Parameters:

appid - the new app id (name)

getObjectURI

public String getObjectURI()

Description copied from interface: ParaObject

The URI of this object. For example: /users/123

Specified by:

getObjectURI in interface ParaObject

Returns:

the URI

See Also:

Utils.getObjectURI(com.erudika.para.core.ParaObject, boolean, boolean)

getTags

public List<String> getTags()

Description copied from interface: ParaObject

The tags associated with this object. Tags must not be null or empty.

Specified by:

getTags in interface ParaObject

Returns:

a set of tags, or an empty set

See Also:

Tag

setTags

public void setTags(List<String> tags)

Description copied from interface: ParaObject

Merges the given tags with existing tags.

Specified by:

setTags in interface ParaObject

Parameters:

tags - the additional tags, or clears all tags if set to null

getStored

public Boolean getStored()

Description copied from interface: ParaObject

Boolean flag which controls whether this object is stored in the database or not. Default is true.

Specified by:

getStored in interface ParaObject

Returns:

true if this object is stored in DB.

setStored

public void setStored(Boolean stored)

Description copied from interface: ParaObject

Sets the "isStored" flag.

Specified by:

setStored in interface ParaObject

Parameters:

stored - when set to true, object is stored in DB.

getIndexed

public Boolean getIndexed()

Description copied from interface: ParaObject

Boolean flag which controls whether this object is indexed by the search engine. Default is true.

Specified by:

getIndexed in interface ParaObject

Returns:

true if this object is indexed

setIndexed

public void setIndexed(Boolean indexed)

Description copied from interface: ParaObject

Sets the "isIndexed" flag.

Specified by:

setIndexed in interface ParaObject

Parameters:

indexed - when set to true, object is indexed.

getCached

public Boolean getCached()

Description copied from interface: ParaObject

Boolean flag which controls whether this object is cached. Default is true.

Specified by:

getCached in interface ParaObject

Returns:

true if this object is cached on update() and create().

setCached

public void setCached(Boolean cached)

Description copied from interface: ParaObject

Sets the "isCached" flag.

Specified by:

setCached in interface ParaObject

Parameters:

cached - when set to true, object is cached.

getTimestamp

public Long getTimestamp()

Description copied from interface: ParaObject

The time when the object was created, in milliseconds.

Specified by:

getTimestamp in interface ParaObject

Returns:

the timestamp of creation

setTimestamp

public void setTimestamp(Long timestamp)

Description copied from interface: ParaObject

Sets the timestamp.

Specified by:

setTimestamp in interface ParaObject

Parameters:

timestamp - a new timestamp in milliseconds.

getCreatorid

public String getCreatorid()

Description copied from interface: ParaObject

The id of the user who created this. Should point to a User id.

Specified by:

getCreatorid in interface ParaObject

Returns:

the id or null

setCreatorid

public void setCreatorid(String creatorid)

Description copied from interface: ParaObject

Sets a new creator id. Must not be null or empty.

Specified by:

setCreatorid in interface ParaObject

Parameters:

creatorid - a new id

getName

public String getName()

Description copied from interface: ParaObject

The name of the object. Can be anything.

Specified by:

getName in interface ParaObject

Returns:

the name. default: [type id]

setName

public void setName(String name)

Description copied from interface: ParaObject

Sets a new name. Must not be null or empty.

Specified by:

setName in interface ParaObject

Parameters:

name - the new name

getPlural

public String getPlural()

Description copied from interface: ParaObject

The plural name of the object. For example: user - users

Specified by:

getPlural in interface ParaObject

Returns:

the plural name

getParentid

public String getParentid()

Description copied from interface: ParaObject

The id of the parent object.

Specified by:

getParentid in interface ParaObject

Returns:

the id of the parent or null

setParentid

public void setParentid(String parentid)

Description copied from interface: ParaObject

Sets a new parent id. Must not be null or empty.

Specified by:

setParentid in interface ParaObject

Parameters:

parentid - a new id

getUpdated

public Long getUpdated()

Description copied from interface: ParaObject

The last time this object was updated. Timestamp in ms.

Specified by:

getUpdated in interface ParaObject

Returns:

timestamp in milliseconds

setUpdated

public void setUpdated(Long updated)

Description copied from interface: ParaObject

Sets the last updated timestamp.

Specified by:

setUpdated in interface ParaObject

Parameters:

updated - a new timestamp

create

public String create()

Description copied from interface: ParaObject

Stores this object in the data store.

Specified by:

create in interface ParaObject

Returns:

the id of the object (a new id if object is new)

See Also:

Stored, DAO.create(com.erudika.para.core.ParaObject)

update

public void update()

Description copied from interface: ParaObject

Updates the object permanently. Changes to Locked fields are ignored.

Specified by:

update in interface ParaObject

See Also:

Locked, DAO.update(com.erudika.para.core.ParaObject)

delete

public void delete()

Description copied from interface: ParaObject

Deletes the object permanently by removing it from the data store.

Specified by:

delete in interface ParaObject

See Also:

DAO.delete(com.erudika.para.core.ParaObject)

exists

public boolean exists()

Description copied from interface: ParaObject

Checks if an object is stored in the data store.

Specified by:

exists in interface ParaObject

Returns:

true if the object is persisted to the data store.

See Also:

DAO.read(java.lang.String)

voteUp

public boolean voteUp(String userid)

Description copied from interface: Votable

Upvotes the object.

Specified by:

voteUp in interface Votable

Parameters:

userid - id of voter

Returns:

true if successful

voteDown

public boolean voteDown(String userid)

Description copied from interface: Votable

Downvotes the object.

Specified by:

voteDown in interface Votable

Parameters:

userid - id of voter

Returns:

true if successful

getVotes

public Integer getVotes()

Description copied from interface: Votable

Returns the total sum of all votes for this object. For example: (+6) + (-4) = 2

Specified by:

getVotes in interface Votable

Returns:

the total sum of votes

setVotes

public void setVotes(Integer votes)

Description copied from interface: Votable

Sets the total votes for this object.

Specified by:

setVotes in interface Votable

Parameters:

votes - the number of votes

getVersion

public Long getVersion()

Description copied from interface: ParaObject

Returns the version number for this object. Used primarily for optimistic locking.

Specified by:

getVersion in interface ParaObject

Returns:

a positive number, 0 if unused or -1, indicating a failed update.

setVersion

public void setVersion(Long version)

Description copied from interface: ParaObject

Sets the version of this object. This value should come from the database.

Specified by:

setVersion in interface ParaObject

Parameters:

version - a positive number, different than the current value of the version field

countLinks

public Long countLinks(String type2)

Description copied from interface: Linkable

Count the total number of links between this object and another type of object.

Specified by:

countLinks in interface Linkable

Parameters:

type2 - the other type of object

Returns:

the number of links

getLinks

public List<Linker> getLinks(String type2,
                             Pager... pager)

Description copied from interface: Linkable

Returns all links between this type object and another type of object.

Specified by:

getLinks in interface Linkable

Parameters:

type2 - the other type of object

pager - a Pager

Returns:

a list of Linker objects in a many-to-many relationship with this object.

getLinkedObjects

public <P extends ParaObject> List<P> getLinkedObjects(String type,
                                                       Pager... pager)

Description copied from interface: Linkable

Similar to Linkable.getChildren(java.lang.String, com.erudika.para.utils.Pager...) but for many-to-many relationships.

Specified by:

getLinkedObjects in interface Linkable

Type Parameters:

P - type of linked objects

Parameters:

type - type of linked objects to look for

pager - a Pager

Returns:

a list of linked objects

findLinkedObjects

public <P extends ParaObject> List<P> findLinkedObjects(String type,
                                                        String field,
                                                        String query,
                                                        Pager... pager)

Description copied from interface: Linkable

Similar to Linkable.findChildren(java.lang.String, java.lang.String, com.erudika.para.utils.Pager...) but for many-to-many relationships. Searches through all linked objects connected to this via a Linker object.

Specified by:

findLinkedObjects in interface Linkable

Type Parameters:

P - type of linked objects

Parameters:

type - type of linked objects to look for

field - the name of the field to target (within a nested field "nstd")

query - a query string

pager - a Pager

Returns:

a list of linked objects matching the search query

isLinked

public boolean isLinked(String type2,
                        String id2)

Description copied from interface: Linkable

Checks if this object is linked to another.

Specified by:

isLinked in interface Linkable

Parameters:

type2 - the other type

id2 - the other id

Returns:

true if the two are linked

isLinked

public boolean isLinked(ParaObject toObj)

Description copied from interface: Linkable

Checks if a given object is linked to this one.

Specified by:

isLinked in interface Linkable

Parameters:

toObj - the other object

Returns:

true if linked

link

public String link(String id2)

Description copied from interface: Linkable

Links an object to this one in a many-to-many relationship. Only a link is created. Objects are left untouched. The type of the second object is automatically determined on read.

Specified by:

link in interface Linkable

Parameters:

id2 - the other id

Returns:

the id of the Linker object that is created

unlink

public void unlink(String type,
                   String id2)

Description copied from interface: Linkable

Unlinks an object from this one. Only a link is deleted. Objects are left untouched.

Specified by:

unlink in interface Linkable

Parameters:

type - the other type

id2 - the other id

unlinkAll

public void unlinkAll()

Description copied from interface: Linkable

Unlinks all objects that are linked to this one. Deletes all Linker objects. Only the links are deleted. Objects are left untouched.

Specified by:

unlinkAll in interface Linkable

countChildren

public Long countChildren(String type)

Description copied from interface: Linkable

Count the total number of child objects for this object.

Specified by:

countChildren in interface Linkable

Parameters:

type - the other type of object

Returns:

the number of links

getChildren

public <P extends ParaObject> List<P> getChildren(String type,
                                                  Pager... pager)

Description copied from interface: Linkable

Returns all child objects linked to this object.

Specified by:

getChildren in interface Linkable

Type Parameters:

P - the type of children

Parameters:

type - the type of children to look for

pager - a Pager

Returns:

a list of ParaObject in a one-to-many relationship with this object

getChildren

public <P extends ParaObject> List<P> getChildren(String type,
                                                  String field,
                                                  String term,
                                                  Pager... pager)

Description copied from interface: Linkable

Returns all child objects linked to this object.

Specified by:

getChildren in interface Linkable

Type Parameters:

P - the type of children

Parameters:

type - the type of children to look for

field - the field name to use as filter

term - the field value to use as filter

pager - a Pager

Returns:

a list of ParaObject in a one-to-many relationship with this object

findChildren

public <P extends ParaObject> List<P> findChildren(String type,
                                                   String query,
                                                   Pager... pager)

Description copied from interface: Linkable

Search through all child objects. Only searches child objects directly connected to this parent via the parentid field.

Specified by:

findChildren in interface Linkable

Type Parameters:

P - the type of children

Parameters:

type - the type of children to look for

query - a query string

pager - a Pager

Returns:

a list of ParaObject in a one-to-many relationship with this object

deleteChildren

public void deleteChildren(String type)

Description copied from interface: Linkable

Deletes all child objects permanently.

Specified by:

deleteChildren in interface Linkable

Parameters:

type - the children's type.

hashCode

public int hashCode()

Overrides:

hashCode in class Object

equals

public boolean equals(Object obj)

Overrides:

equals in class Object

toString

public String toString()

Overrides:

toString in class Object