Usage
=====

Entity Relationship Diagram allows the creation of Entity Relationship Diagrams to describe
entities, their attributes and the relationships between them.

Entities are created and attributes added to them.
Attributes have a name and type and may be identified as a key.
Entities are then added to the Entity Relationship Diagram.

Relationships between entities are defined and added to the Entity Relationship Diagram, which is then rendered.

Example
-------

PHP
+++

.. code-block:: php

    $customer = (new Entity('CUSTOMER'))
        ->withAttribute(
            (new Attribute('customerId', 'int'))->withKey(Key::primaryKey),
            new Attribute('name', 'string'),
            new Attribute('sector', 'string')
        )
    ;

    $deliveryAddress = (new Entity('DELIVERY-ADDRESS'))
        ->withAttribute(
            (new Attribute('customerId', 'int'))->withKey(Key::foreignKey),
            new Attribute('streetAddress', 'string'),
            new Attribute('locality', 'string'),
            new Attribute('region', 'string'),
            new Attribute('postalCode', 'string'),
            new Attribute('country', 'string')
        )
    ;

    $order = (new Entity('ORDER'))
        ->withAttribute(
            (new Attribute('orderNumber', 'int'))->withKey(Key::primaryKey),
            (new Attribute('customerId', 'int'))->withKey(Key::foreignKey)
        )
    ;

    $lineItem = (new Entity('LINE-ITEM'))
        ->withAttribute(
            (new Attribute('orderNumber', 'int'))->withKey(Key::foreignKey),
            new Attribute('productCode', 'string'),
            new Attribute('quantity', 'int'),
            new Attribute('float', 'pricePerUnit')
        )
    ;

    echo Mermaid::create(EntityRelationshipDiagram::class)
        ->withEntity($customer, $deliveryAddress, $order, $lineItem)
        ->withRelationship(
            new Relationship(
                $customer,
                Cardinality::oneOrMore,
                $deliveryAddress,
                Cardinality::oneOrMore,
                RelationshipType::nonIdentifying,
                'uses'
            ),
            new Relationship(
                $customer,
                Cardinality::exactlyOne,
                $order,
                Cardinality::zeroOrOne,
                RelationshipType::identifying,
                'places'
            ),
            new Relationship(
                $order,
                Cardinality::exactlyOne,
                $lineItem,
                Cardinality::oneOrMore,
                RelationshipType::identifying,
                'contains'
            ),
        )
        ->render()
    ;

Generated Mermaid
+++++++++++++++++

::

    <pre class="mermaid">
    erDiagram
    direction TB
    CUSTOMER {
      int customerId PK
      string name
      string sector
    }
    DELIVERY-ADDRESS {
      int customerId FK
      string streetAddress
      string locality
      string region
      string postalCode
      string country
    }
    ORDER {
      int orderNumber PK
      int customerId FK
    }
    LINE-ITEM {
      int orderNumber FK
      string productCode
      int quantity
      float pricePerUnit
    }
    CUSTOMER }|..|{ DELIVERY-ADDRESS : uses
    CUSTOMER ||--o{ ORDER : places
    ORDER ||--|{ LINE-ITEM : contains
    </pre>

Mermaid Diagram
+++++++++++++++

.. mermaid::

    erDiagram
    direction TB
    CUSTOMER {
      int customerId PK
      string name
      string sector
    }
    DELIVERY-ADDRESS {
      int customerId FK
      string streetAddress
      string locality
      string region
      string postalCode
      string country
    }
    ORDER {
      int orderNumber PK
      int customerId FK
    }
    LINE-ITEM {
      int orderNumber FK
      string productCode
      int quantity
      float pricePerUnit
    }
    CUSTOMER }|..|{ DELIVERY-ADDRESS : uses
    CUSTOMER ||--o{ ORDER : places
    ORDER ||--|{ LINE-ITEM : contains