eZ Components - Tree ~~~~~~~~~~~~~~~~~~~~ .. contents:: Table of Contents Introduction ============ The Tree component is all about tree structures. It allows you to maintain a hierarchical relation between nodes. The component provides many operations on trees, and the node in the trees as well. Because there are different algorithms for storing tree structures in a relational database—each with different properties—the component supports multiple backends. The Tree component itself comes with a memory (ezcTreeMemory) and XML (ezcTreeXml) backend. The TreeDatabaseTiein component provides three backends that store the tree structure in a database table. Besides storing the hierarchical data itself, the component also allows you to associate data with those tree nodes. The data is store through a data store. Depending on backends different data stores are available as you can see in the following table: =============================== =========================================================================== Backend Data Stores =============================== =========================================================================== ezcTreeMemory ezcTreeMemoryDataStore ezcTreeXml ezcTreeXmlInternalDataStore ezcTreeDbMaterializedPath [1]_ ezcTreeDbExternalTableDataStore [1]_, ezcTreePersistentObjectDataStore [2]_ ezcTreeDbNestedSet [1]_ ezcTreeDbExternalTableDataStore [1]_, ezcTreePersistentObjectDataStore [2]_ ezcTreeDbParentChild [1]_ ezcTreeDbExternalTableDataStore [1]_, ezcTreePersistentObjectDataStore [2]_ =============================== =========================================================================== .. [1] Available through the TreeDatabaseTiein_ component .. [2] Available through the TreePersistentObjectTiein_ component Dependencies ============ From the table and comments above it becomes apparent that there are a few optional dependencies. Through the TreeDatabaseTiein_ and TreePersistentObjectTiein_ components additional functionality becomes available. Class overview ============== ezcTreeMemory, ezcTreeXml Two classes available without installing Tieins that implement the storing of tree data in-memory, or in an XML file. There is a matching data store for each of those two classes (ezcTreeMemoryDataStore and ezcTreeXmlInternalDataStore respectively). ezcTreeDbMaterializedPath, ezcTreeDbNestedSet, ezcTreeDbParentChild Three backends that are made available through the TreeDatabaseTiein_ component. Each of them implements a different strategy for storing the relations between nodes. Depending on the application a specific backend should be chosen. More about that in the section Backends_. ezcTreeNode Represents one node of the tree. Objects of this class can be added to the tree. The object stores both the ID and data belonging to the node. Data is always fetched on-demand, unless a ezcTreeNodeListIterator is used with the prefetch option. ezcTreeNodeListIterator This class can be used to iterate over an ezcTreeNodeList which is returned by many of the node fetching operations (see the ezcTree documentation for which operations are supported). It is advised to use this class to iterate over the nodes and not simply use foreach() on a returned ezcTreeNodeList because this class also supports pre-fetching of associated data, which can drastically reduce the amount of queries being run in case a database based data store is used (such as ezcTreeDbExternalTableDataStore or ezcTreePersistentObjectDataStore). Basic usage =========== To use a tree, you will need both a tree backend (a class inherited from ezcTree), and a data store (implementation of the ezcTreeDataStore interface). The following example shows you how to instantiate a new tree object making use of the ezcTreeXml backend and the ezcTreeXmlInternalDataStore data store: .. include:: tutorial_example_basic.php :literal: Line 4 and 5 define the data store and the tree. The parameters to ezcTree's constructor specify which file to use, and which data store. After opening the tree lines 7 and 8 demonstrate how to fetch a node from the tree by using the node ID, and then access the data that belongs to the node. IDs can be either integer numbers or strings. There are a few restrictions to using strings as IDs however. The string IDs needs to: #. be a valid PHP array key #. consist of XML NameChar_ characters only .. _NameChar: http://www.w3.org/TR/2000/WD-xml-2e-20000814#NT-NameChar Memory trees can never be instantiated, because there is no permanent storage available. They will always have to be created from scratch or created from another tree by using the ezcTree::copy() method. Operations on trees ------------------- Besides fetching nodes, it is of course possible to run many operations on the trees and nodes. In the following example you can see two different ways of operations, on the tree, or on nodes. .. include:: tutorial_example_treeops.php :literal: Lines 7 to 11 show how to figure out whether a node is a descendant of another node. Most of the operations can also be done directly on the tree by using the node IDs. You can see that in lines 13 to 16. All operations are implemented on the tree level, so using the syntax in lines 13 to 16 will result in slightly higher performance. Lines 18 to 23 demonstrate another tree operation, fetching a sub-tree. All operations that can return more than one node, do so as an ezcTreeNodeList. Please refer to the ezcTreeNode documentation for a full list of supported operations. Iterating over a node list -------------------------- When you iterate over a node list manually such as the previous examples showed will fetch the associated data on-demand - at the moment the ->data property of a node is requested. If you have a large node list as result this could cause many database queries if you are using a database based backend and data store. In such cases you might want to fetch all data in on go - with one query. The ezcTreeNodeListIterator class allows you to do this: .. include:: tutorial_example_iterator.php :literal: In line 7 we use the ezcTree->fetchChildren() method to find all the direct children of the node with ID "NobleGasses". Then in lines 10 to 13 we create a ezcTreeNodeListIterator over the returned ezcTreeNodeList $noble. The first parameter is the tree, the second one the node list and the third parameter whether data should be prefixed or not. Creating and modifying a tree ----------------------------- If you want to create a new tree, then instead of instantiating a tree you use the overloaded ezcTree::create() factory method. Once a tree and associated store are created you can proceed to fill the tree with nodes. The example below demonstrates that: .. include:: tutorial_example_create.php :literal: In line 5 we create a new tree by using the ezcTreeXml::create() factory method. The name of the file is the first argument and the data store the second argument again. This will create a totally empty tree without nodes or even a root node. In lines 7 and 8 we then create a new node with the ezcTree->createNode() method which accepts the node ID and node data value as arguments. The ezcTreeDbExternalTableDataStore data store also supports compound data values, as you can see in the documentation of ezcTreeDbExternalTableDataStore->__construct(). Lines 10 to 13 proceed to add two new nodes to the $rootNode and lines 15-26 the add further nodes to the $nonMetal and $nobleGasses nodes. This example creates the XML file that is used in the other examples in this tutorial. Backends ======== Non-database backends --------------------- The Tree component comes with two generic backends, one that stores the tree structure in an XML file, and another one that only keeps a tree structure in memory. The XML backend uses PHP's DOM functionality to parse the tree and thus will the whole tree structure be loaded into memory when an ezcTreeXml object is instantiated. The ezcTreeMemory backend has to be created from scratch when it used, however it is also possible to copy an ezcTreeXml based tree to a memory based one. The example below shows that: .. include:: tutorial_example_copy_tree.php :literal: Operations on tree based on ezcTreeMemory are of course faster than operations on trees based on ezcTreeDb or ezcTreeXml. Database based backends ----------------------- By installing the TreeDatabaseTiein_ and TreePersistentObjectTiein_ components a few more backends and data stores are available. There are three new backends: #. ezcTreeDbParentChild - Uses the ID of the parent to keep track of the structure only. #. ezcTreeDbNestedSet - Uses left/right values in addition to the parent ID that the ezcTreeDbParentChild backend uses to keep track of the tree structure. #. ezcTreeDbMaterializedPath - Uses /1/2/4/6/19/24 style paths to store the tree structure. Each of those three backends have different performance related properties depending on which operation is run. The following table tries to summarize some of the properties of each algorithm: +----------------------------+-----------------------------------------------------------------------+ | Operation | Backends | | +----------------------+-------------------------+----------------------+ | | Parent Child | Nested set | Materialized Path | +============================+======================+=========================+======================+ | addChild() | *Simple operation.* | Possible long, as on | *Simple operation.* | | | | average the left and | | | | | right values of half of | | | | | the nodes in the tree | | | | | have to be updated. | | +----------------------------+----------------------+-------------------------+----------------------+ | delete() | Recursive operation | *Simple operation.* | *Simple operation.* | | | to find a whole | | but query has to | | | tree. | | use LIKE. | +----------------------------+----------------------+-------------------------+----------------------+ | fetchChildren() | *Simple operation.* | *Simple operation.* | *Simple operation.* | +----------------------------+----------------------+-------------------------+----------------------+ | fetchNodeById() | *Simple operation.* | *Simple operation.* | *Simple operation.* | +----------------------------+----------------------+-------------------------+----------------------+ | fetchParent() | *Simple operation.* | *Simple operation.* | *Simple operation.* | +----------------------------+----------------------+-------------------------+----------------------+ | fetchPath() | Recursive operation | *Simple operation.* | *Simple operation.* | | | to iterate over the | | | | | parents all the way | | | | | to the root node. | | | | | | | | +----------------------------+----------------------+-------------------------+----------------------+ | fetchSubtreeBreadthFirst() | Recursive operation | Recursive operation to | Recursive operation | | | to find the whole | find the whole subtree | to find the whole | | | subtree - order of | - order of nodes for | subtree - order of | | | nodes for each level | each level is not | nodes for each level | | | is not guaranteed. | guaranteed. | is not guaranteed. | +----------------------------+----------------------+-------------------------+----------------------+ | fetchSubtreeDepthFirst() | Recursive operation | Simple operation - | *Simple operation.* | | | to find the whole | order of nodes is the | but query has to use | | | subtree - order of | same order as in they | LIKE - order of | | | nodes is not | were added. | nodes is not | | | guaranteed. | | guaranteed. | +----------------------------+----------------------+-------------------------+----------------------+ | getChildCount() | *Simple operation.* | *Simple operation.* | *Simple operation.* | +----------------------------+----------------------+-------------------------+----------------------+ | getChildCountRecursive() | Recursive operation | *Simple operation.* | *Simple operation.* | | | to find the nodes in | | but query has to use | | | the whole subtree. | | LIKE. | | | | | | | | | | | +----------------------------+----------------------+-------------------------+----------------------+ | getPathLength() | Recursive operation | *Simple operation.* | *Simple operation.* | | | to iterate over the | | | | | parents all the way | | | | | to the root node. | | | +----------------------------+----------------------+-------------------------+----------------------+ | hasChildNodes() | *Simple operation.* | *Simple operation.* | *Simple operation.* | +----------------------------+----------------------+-------------------------+----------------------+ | isChildOf() | *Simple operation.* | *Simple operation.* | *Simple operation.* | +----------------------------+----------------------+-------------------------+----------------------+ | isDescendantOf() | Recursive operation | *Simple operation.* | *Simple operation.* | | | to iterate over the | | | | | parents until either | | | | | the root node or | | | | | when the node is | | | | | found. | | | +----------------------------+----------------------+-------------------------+----------------------+ | isSiblingOf() | *Simple operation.* | *Simple operation.* | *Simple operation.* | +----------------------------+----------------------+-------------------------+----------------------+ | move() | *Simple operation.* | Possible long, as on | All the nodes in the | | | | average the left and | subtree that is | | | | the right values of | moved need to be | | | | half of the nodes need | updated - this is | | | | to be updated - twice. | done with string | | | | | operations. | +----------------------------+----------------------+-------------------------+----------------------+ | nodeExists() | *Simple operation.* | *Simple operation.* | *Simple operation.* | +----------------------------+----------------------+-------------------------+----------------------+ | setRootNode() | *Simple operation.* | *Simple operation.* | *Simple operation.* | +----------------------------+----------------------+-------------------------+----------------------+ Data stores ``````````` The database backends that the TreeDatabaseTiein_ component provide also support two different data stores. One of them, ezcTreeDbExternalTableDataStore, comes with the TreeDatabaseTiein_ component. Another one, ezcTreePersistentObjectDataStore is provided through the TreePersistentObjectTiein_ component. Database table ++++++++++++++ The ezcTreeDbExternalTableDataStore can be used in two different modes. In the first you specify a database field that is matched against the node's ID, and another field that is used for the "data" property belonging to a node. The next example shows that: .. include:: tutorial_example_database_one_field.php :literal: In this example lines 4 to 22 set up the database and database tables. Please refer to the specific database backend's documentation for full information on what the different tables should look like. In this case I have to point out, that for the data store we only create two fields though: node_id and data_field. We can see that back in line 24, where we instantiate the store object. We specify the database object, the name of the data table ('data'), the field that is matched against the node ID ('node_id') and which field to use for data ('data_field'). In lines 27 to 30 we then insert some sample nodes and line 32 demonstrates the retrieval of data. In the second mode, we do not specify a field to use to fetch data from: .. include:: tutorial_example_database_multi_field.php :literal: Differences with the previous example are the data table definition in lines 17 to 21. Instead of defining a specific data field to use there are now multiple fields ('melting_temp_k' and 'boiling_temp_k'). The instantiation of the data store in line 27 now misses the fourth argument as well. The data that is specified when creating a node now consists of an array describing all the fields in the database table, except for the 'node_id' as that one is implicit. When fetching the data the whole table record is returned, minus the 'node_id' field. Persistent Object +++++++++++++++++ The ezcTreePersistentObjectDataStore brings multiple data fields even further and extends the Tree to use persistent objects as data for the tree nodes. .. include:: tutorial_example_persistent_object.php :literal: The database tables are setup just like the previous example in lines 5 to 24. Lines 26 to 32 then continue to use the DatabaseSchema_ component to write persistent definition files and class stubs. The store is setup in lines 35 and 36. The ezcTreePersistentObjectDataStore uses the ezcPersistentSession as the first argument and then the object's class and object's ID property as second and third arguments. Unlike the previous example you should specify the class and property names of the persistent objects that you are storing, and *not* the table name and ID field. Lines 39 to 48 then show how data is inserted into the tree, and how it is retrieved. You will most likely have to tune the classes that are generated for you in a real life situation, as the generated classes (line 29 and 31) only have private properties and the getState() and setState() methods that persistent objects are required to have. Please refer to the PersistentObject_ documentation for more information. Visualization ============= Sometimes it's useful to visualize a tree structure. The Tree component has some functionality for this in the form of different visualizers. There are currently two possibilities. Text based visualization ------------------------ The ezcTreeVisitorPlainText class implements a visitor pattern to render a tree for the console. Both latin1 and utf-8 are supported as character sets, where the utf-8 version looks much better. The following example shows how to generated a text based representation of the tree from the first example in this tutorial: .. include:: tutorial_example_text_tree.php :literal: The output is:: Elements ├─NonMetals │ ├─H │ ├─C │ ├─N │ ├─O │ ├─P │ ├─S │ └─Se └─NobleGasses ├─F ├─Cl ├─Br └─I GraphViz based visualization ---------------------------- In case you are not on the console, it is also possible to render the tree as a GraphViz .dot file that then can be used to generate an image - for example a PNG image. The next example shows the use of the ezcTreeVisitorGraphViz class: .. include:: tutorial_example_graphviz.php :literal: The generated .dot file can be converted to an image by running the following command:: dot -Tpng -o img/graphviz.png files/graphviz.dot The result of that is (scaled): .. figure:: img/graphviz.png .. _DatabaseSchema: introduction_DatabaseSchema.html .. _PersistentObject: introduction_PersistentObject.html .. _TreeDatabaseTiein: introduction_TreeDatabaseTiein.html .. _TreePersistentObjectTiein: introduction_TreePersistentObjectTiein.html .. Local Variables: mode: rst fill-column: 79 End: vim: et syn=rst tw=79 spell