README

database - v1.9.0
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This library provides a really simple PDO database connection wrapper in
addition to providing several database abstraction mechanisms for representing
database entities and schemas. This package is designed to eliminate boilerplate
associated with connecting to the database and managing credentials. Note that
this library does not provide fine-tuned query abstractions.

While targeting PDO lets the library use any database engine, the abstractions
code has been tested and developed for use with MySQL. That isn't to say it
won't necessarily work with another database engine though. You might have more
of a problem with compatibility with the Entity framework classes.

Primary authors:

    Roger Gee <roger.gee@tulsalibrary.org>

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Installing

This library is available as a composer package. Require 'tccl/database' in your
composer.json file and then install.

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Classes

    TCCL\Database\DatabaseConnection
        Wraps PDO to represent a database connection

    TCCL\Database\Entity
        Provides an abstraction for managing a single entity

    TCCL\Database\EntityInsertSet
        Provides an abstraction for inserting multiple Entity objects

    TCCL\Database\EntityList
        Provides an abstraction for manipulating lists of database entities

    TCCL\Database\Schema
        Provides abstraction for defining and installing schemas

    TCCL\Database\ReflectionEntity
        Provides an Entity abstraction where metadata is obtained from doc comments

    TCCL\Database\ReflectionEntityTrait
        Used with ReflectionEntity

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Usage

[DatabaseConnection]

Use a DatabaseConnection instance to manage a database connection. The
connection parameters are to be stored in the $GLOBALS superglobal. The bucket
under this array is arbitrary and may be arbitrarily nested. The structure of
the bucket is an indexed array with three parts like:

    <?php

    $dbconfig = array(
        'mysql:host=localhost;dbname=db', // connection string
        'user', // database user
        'password', // database user password
    );

When initializing a database connection, pass in the keys that index $GLOBALS to
get to the database array bucket. For example, to load the database info from
the global variable from the last example (i.e. $dbconfig):

    <?php

    $conn = new \TCCL\Database\DatabaseConnection('dbconfig');

If you've nested the array down, specify a parameter list to the constructor:

    <?php

    define('CONFIG','my-app');
    $GLOBALS['a']['b'][CONFIG]['dbinfo'] = array( /* ... */ );
    $conn = new \TCCL\Database\DatabaseConnection('a','b',CONFIG,'dbinfo');

It may be useful to extend DatabaseConnection and implement a singleton
pattern. The constructor of your subclass should take care of passing in the
correct keys to its parent constructor. Note that a singleton pattern is not
entirely necessary since the DatabaseConnection caches PDO instances in a static
class property.

Provided methods:

    function query($query,$args = null /* ... */)

        Runs a query as a prepared statement. Args may be a single array
        specifying all the query parameters or the first argument in a parameter
        list. Alternatively no $args can be specified if the parameter is
        omitted, though you might just use rawQuery() for performance.

        Example:

            $conn->query('SELECT * FROM table WHERE a = ? and b = ?',$a,$b);
                OR
            $conn->query('SELECT * FROM table WHERE a = ? and b = ?',[$a,$b]);

    function rawQuery($query)

        Runs a query directly (no filtering). Depending on the underlying
        driver, you may be able to run more than one statement in a single
        query string.

    function prepare($query)

        Wraps PDO::prepare().

    function getPDO()

        Gets the underlying PDO connection instance.

    function beginTransaction()

        Wraps PDO::beginTransaction(); however the transaction is reference
        counted so multiple contexts can pretend to have a transaction (they
        really just share the same transaction).

    function endTransaction()

        Wraps PDO::endTransaction(); reference counting is employed in tandem
        with DatabaseConnection::beginTransaction().

    function rollback()

        Wraps PDO::rollback(); this resets the reference counter. Therefore it's
        the responsiblity of the caller to properly unwind each context (hint:
        throwing an Exception is typically a good way to implement this).

    function lastInsertId()

        Wraps PDO::lastInsertId().

[Entity]

Use the Entity class to define a data model in an application with an
object-oriented interface. This model should map to a single core entity in the
database schema, though you can write hooks to handle other entities as
well. The Entity class is abstract: to use the class, you simply have to define
a constructor that calls the parent, Entity constructor. Then you register
fields on the Entity. The fields you register become dynamic properties on the
object, and you can define filters and aliases for fields as well. The Entity
class can write queries for you to fetch (i.e. SELECT), INSERT and UPDATE an
entity. However you can override queries to provide you own implementations for
more advanced scenarios. This is useful for providing virtual fields which may
be the result of JOINing on other tables.

For example, consider the following schema:

    CREATE TABLE person (
        id INT NOT NULL AUTO_INCREMENT,
        name VARCHAR(128),
        nationality VARCHAR(128),
        dob DATETIME,
        favorite_integer INT,

        PRIMARY KEY (id)
    );

An Entity that models this might look like:

    <?php

    class Person extends Entity {
        public function __construct($id = null) {
            $keys = ['id' => $id];
            parent::__construct(get_db_conn(),'person',$keys);
            $this->registerField('id','personId',null,'intval');
            $this->registerField('name');
            $this->registerField('nationality',null,'American');
            $this->registerField('dob','dateOfBirth',null,'date_create');
            $this->registerField('favorite_integer','favInt',null,'intval');
        }

        /**
         * Overrides Entity::processCommitFields().
         */
        protected function processCommitFields(array $fields) {
            if (isset($fields['dob'])) {
                $fields['dob'] = $fields['dob']->format('Y-m-d H:i:s');
            }
        }
    }

Every entity constructor receives a DatabaseConnection object, a table name and
a list of keys. Optionally you can specify a fourth parameter that indicates the
create state of an Entity. The $keys array specifies which fields act as keys
when fetching an entity or creating a new entity. It's worth noting that a key
name of 'id' has a special meaning for when a new entity is INSERTed into the
database and should typically be used. The key value can be null, which
indicates the new Entity is a candidate for creation. Otherwise the object will
attempt a lookup on an existing entity.

The registerField() method defines the result fields from the fetch query. By
default you can define this or some subset of the table fields. However if you
override the query by overriding getFetchQuery(), you can define a field for a
subset of that query's result set. This method also allows you to define
aliases; note that these aliases are only used in the object and not in any
queries. If you use aliases in a custom query, they will be used for the field
name just like with any PDO result set. Optionally you can define a default
value for a field (useful for new entities) and a filter callback for
transforming the string database result into some other PHP type. The filter
callback is only used when fetching an existing entity.

In the example, the 'dateOfBirth' field is an alias for the table field
'dob'. The actual field on the Entity object will be a DateTime instance,
created by filtering the date string through the date extension's date_create()
function.

Fields are accessed like public properties on Entity objects. If you specified
an alias, you must use the alias name. Otherwise, the table field name is
valid. Here's an example:

    <?php

    $id = 5; // assume there is person with id=5

    $person = new Person($id);
    var_dump($person->name);

This example looks up the name of the person entity with id=5. An Entity
lazy-loads its fields, so the actual query doesn't happen until first access.

When writing a field, the Entity marks that field as dirty. Then when you commit
the entity, only the dirty fields are used to INSERT/UPDATE the entity. The
Entity keeps track of whether it exists or not, deduced from the $keys parameter
to the Entity constructor. You can query whether an Entity exists via the
exists() method.

The following example creates a new Entity:

    <?php

    $bob = new Person;
    $bob->name = 'Bob';
    $bob->favInt = 56;
    $bob->dateOfBirth = new DateTime('1993-09-14 00:00:00');
    $bob->commit();

    var_dump($bob->id);

Since the 'id' field is handled specially by the functionality, it gets the
insert ID from the underlying query result. The commit() method returns true if
the Entity was created or updated. Be careful with this, since it may return
false if an update/insert was empty.

Special features:

    - Call $entity->setUpdateOnly(true) to prevent accidental creation of an
      entity having keys that do not map to an existing entity. This can also be
      prevented by calling exists() to make sure the entity exists.

    - An associative array of the fields can be retrieved via
      $entity->getFields(). A flag to this method controls whether the keys are
      the property names (i.e. includes aliases) or the table field names.

    - Call $entity->invalidate() to forget about fetched field values. This
      means the next access will perform a query and overwrite all fields.

    - Class override API:

        - function getFetchQuery(array &$values)
            Overrides the fetch query; you return the query and write query
            parameters to $values. Use getKeys() to get the key bucket instead
            of accessing object properties. Also, getKeyString() can be used to
            get an SQL snippet suitable for injecting into a WHERE clause.

        - function processFetchResults(array &$fetches)
            Process the results of a fetch before they are applied to the
            object. Values are read from $fetches and written back to $fetches
            as well. Note: the keys in $fetches are the table field names, not
            the aliases.

        - function processCommitFields(array $fields)
            Like processFetchResults() but for values used to commit an
            Entity. Due to the implementation, each bucket in $fields is a
            reference variable, so you can treat $fields as if it was passed by
            reference (when writing array fields). Note: the keys in $fetches
            are the table field names, not the aliases.

        - function preCommit($insert)
            Used to perform a custom hook before a commit has been
            processed. The $insert flag determines if the query mode is INSERT
            or UPDATE. Note: this method is called in a database transaction
            context.

        - function postCommit($insert)
            Like preCommit() but executed after the entity was committed. If an
            'id' was set due to an INSERT, it is guarenteed to be ready for
            consumption by this method.

        NOTE: preCommit() and postCommit() are executed for empty updates but
        not for empty inserts or inserts blocked by setUpdateOnly().

[EntityInsertSet]

This class provides a convenience abstraction to insert multiple entities at
once. However it is not possible to reliably determine the insert IDs this way.

[EntityList]

This class represents a list of entities. In this case, entities are not
represented individually. Instead, they are managed as a group. The list
provides efficient ways to manipulate the list including add, modify and delete
items.

A PHP array type is used to represent an individual list item. The schema for
the entity type is denoted using doc comments or arguments passed into the
constructor.

Example:

    /**
     * @table fruit
     * @key id
     * @field[] name:fruitName:
     * @field[] calories::intval
     */
    class FruitList extends EntityList {
        public function __construct() {
            parent::__construct(Database::getConnection());
        }
    }

An entity list can also contain one or more filters used to narrow the list of
entities (e.g. using a subkey). Filters are SQL fragments utilized when updating
or deleting entities in the list. Filters are NOT considered when creating new
entities: you must make sure to assign appropriate fields. While you can specify
your filter as a single fragment, you can also specify multiple fragments which
will be combined in conjunction.

Filter fragments can have bound parameters. These MUST be positional bound
parameters, indicated via a '?' symbol in the fragment. You can assign bound
parameters in your constructor using the setFilterVariables() method. Note that
the set of filter variables span each fragment in order.

Example: consider a list of employees grouped by department:

/**
 * @table employee
 * @key id
 * @field[] name::
 * @field[] title::
 * @field[] start_date:startDate:
 * @filter[] department = ?
 */
class EmployeeList extends EntityList {
  public function __construct($department) {
    parent::__construct(Database::getSingleton());
    $this->setFilterVariables([
      $department,
    ]);
  }
}

[ReflectionEntity]

Works like Entity but uses reflection to gather table/field metadata. In this
way, you do not register individual fields but supply doc comments that denote
the entity fields/table info.

When you subclass a ReflectionEntity, you must use the ReflectionEntityTrait in
the same class.

/**
 * Represents a 'fruit' entity.
 *
 * @table fruit_record
 */
class Fruit extends ReflectionEntity {
    use ReflectionEntityTrait;

    /**
     * The entity ID.
     *
     * @field id
     * @key
     */
    private $id;

    /**
     * The fruit's common name.
     *
     * @field common_name
     */
    private $name;

    /**
     * The fruit's scientific name.
     *
     * @field scientific_name
     */
    private $scientificName;

    /**
     * The number of calories.
     *
     * @field calories
     */
    private $calories;

    public function __construct($id = null) {
        $this->id = $id;

        $db = /* Get DatabaseConnection instance... */;
        parent::__construct($db);
    }
}

You can inherit ReflectionEntity types. The ReflectionEntity will inherit
schema. If schema are specified in both parent and child classes, then the
functionality will merge. The most-derived class has precedence when it comes to
table names, fields, ETC.

[Schema]

This class provides a way to manage schemas programmatically. Currently, the
functionality only supports creating initial schema, not applying database
updates.

A "Schema" object implements an array interface, so you can denote the schema
using a PHP array. Since the order of table definitions is important, you must
define the tables in the array in the correct order. Table field metadata
(i.e. types, constraints, ETC.) are specified in this array. You should use the
constants defined in class Schema for field sizes and types. Here is an example
that demonstrates all of the capabilities:

    $schema = new Schema;
    $schema['table'] = [
        // Specify primary keys like this. You may specify more than one to get
        // a compound primary key
        'primary keys' => [
            // Field definitions...

            // A SERIAL_TYPE gets AUTO_INCREMENT. You may optionally specify a
            // "size" and "not null" properties.
            'id' => [
                'type' => Schema::SERIAL_TYPE,
                'not null' => true,
            ],
        ],

        // Non-constrained fields are specified here.
        'fields' => [
            // Field definitions...

            // Integer types can have a "size".
            'thing1' => [
                'type' => Schema::INTEGER_TYPE,
                'size' => Schema::SIZE_TINY,
            ],
            'thing2' => [
                'type' => Schema::INTEGER_TYPE,
                'not null' => true,
                'default' => 345,
            ],

            // String types may have a "length".
            'string1' => [
                'type' => Schema::VARCHAR_TYPE,
                'not null' => false,
                'length' => 1024,
            ],

            // NUMERIC types *MUST* specify "precision" and "scale".
            'net_worth' => [
                'type' => Schema::NUMERIC_TYPE,
                'precision' => 9,
                'scale' => 2,
            ],

            'batting_average' => [
                'type' => Schema::FLOAT_TYPE,
            ],
            'memoir' => [
                'type' => Schema::BLOB_TYPE,
                'size' => Schema::SIZE_BIG,
            ],
        ],

        // Foreign keys are specified like this. Do not specify the foreign
        // key field in the "fields" or any other section.
        'foreign keys' => [
            'other_table_id' => [
                // "key" is a single field definition
                'key' => [
                    'type' => DatabaseSchema::INTEGER_TYPE,
                ],

                'table' => 'other_table',
                'field' => 'id',
            ],
        ],

        // Unique keys are specified like this. These reference existing fields.
        'unique keys' => [
            // UNIQUE keys may be compound.
            'unique_thing1' => ['thing1'],
        ],

        // Indexes are specified like this. These reference existing fields.
        'indexes' => [
            'index_thing2' => ['thing2'],
        ],
    ];

To commit the schema, call the "execute" method:

    // $conn = ...
    $schema->execute($conn);

To test your schema generation, just use the object like a string:

    echo "MY SCHEMA: $schema";
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