ORM¶

Means by which data is persisted from objects to a relational database
Magento's ORM is built around models, resource models and resource collections
- Models: Data and behaviour
- Resource Models: Maps data for storage
- Collections: Groups of models, as well as filtering, sorting and paging
- Resources: Database connection adapters

Models¶

Models only can manpulate data
Models don't concern themselves with data persistence
- Models' load(), save(), delete() methods are deprecated
Persisted Models must extend Magento\Framework\Model\AbstractModel
- In the _construct() method, a link to the Resource Model class is specified with $this->_init('Namespaced\Path\To\ResourceModel')

Resource Model contains the primary ID field name
- The resource models' CRUD methods should be used to persist models
- Resource Models extend Magento\Framework\Db\Adapter\Pdo, which extends Zend\Db
In the _construct() method, a link to the main table is specified with $this->_init('table_name', 'primary_key_column');

Implement Magento\Framework\Model\Resource\Db\Collection\AbstractCollection
In the _construct() method, a link to the Model and Resource Model is specified with $this->_init('Namespaced\Path\To\Model', 'Namespaced\Path\To\ResourceModel');
Provide methods
- addFieldToFilter()
- getConnection()
- getSelect()
- addBindParam()
- getIdFieldName()
- distinct()
- addOrder()
- setOrder()
- unshiftOrder()
- getItems()
- getSize()
- getSelectCountSql()
- load()
- resetData()
- walk()
Records are lazy-loaded, the first time a list is accessed
Query operator maps
- eq = =
- neq = !=
- like = like
- nlike = not like
- in = in
- nin = not in
- notnull = is NOT NULL
- null = is NULL
- gt = >
- lt = <
- gteq = >=
- moreq = >=
- lteq = <=
- finset = find_in_set
- from, to = >= and <=

$resourceModel->load($modelId, $field = null)
- A third parameter allows for loading by a non-ID attribute
- EAV models should use loadByAttribute() instead
Models' _beforeLoad() method fires a model_load_before generically, and also specifically for the model
Models' _afterLoad() method fires a model_load_after generically, and also specifically for the model
Useful methods
- save()
- isDeleted()
- hasDataChanges
- validateBeforeSave()
- isSaveAllowed()
- afterCommitCallback()

Install scripts run once per module
Upgrade scripts are run after subsequent updates
Module version is set in (module)etc/module.xml root node's setup_version attribute
Versions are stored in the setup_module table
Installers implement Magento\Framework\Setup\Install(Data|Schema)Interface's install() method
Upgraders implement Magento\Framework\Setup\Upgrade(Data|Schema)Interface's upgrade() method
Should start with $installer = $setup; $installer->startSetup(); and end with $installer->endSetup();
Scripts are run only when bin/magento setup:upgrade is run

Raw SQL as a parameter to the run() method
$installer->getConnection() contains
- newTable()
- createTable()
- addConstraint()
- dropTable()

EAV aims to make data storage across multiple website more flexible
Means the data is stored across multiple tables
Means values and attributes can be decoupled from their entities
Data types
- Meta information: entity type, attributes per entity type, attribute set and groups
- Content: entity records, attribute values

eav_entity_type contains
- entity_type_id
- entity_type_code
- entity_table
- default_attribute_set_id
- increment_model
eav_attribute contains
- attribute_id
- entity_type_id
- attribute_code
- backend_type
- backend_model
- source_model
- frontend_model
(entity_type)_entity contains
- entity_id
- entity_type_id
- Any static attribute type values
(entity_type)_(backend_type) (int, decimal, varchar, text, datetime) contains
- value_id
- entity_type_id
- entity_id
- attribute_id
- value

Like flat table entities, EAV models extend Magento\Framework\Model\AbstractModel
EAV Resource Models however extend Magento\Eav\Entity\AbstractEntity
Magento\Eav\Entity\AbstractEntity provides
- getAttribute() for getting an attribute by code or ID
- saveAttribute() saves only that value, rather than the full entity
- getWriteConnection()
- getEntityTable()
Flat entities are loaded
- $model->load()
- $resourceModel->load()
- (Resource table)
- (Model table)
EAV entities are loaded
- $model->load()
- $resourceModel->load()
- eav_entity_type and eav_attrbute
- (EAV Attributes table)
- (Attribute values tables)
- (Attributes and Values)

EAV Collections have a few methods:
- addAttributeToSelect() adds the attribute values table to the select and the value to the result
- addAttributeToFilter() joins the attribute table to the join and allows filtering
- joinAttribute() joins a value table from another entity's attribute

Attribute columns include:
- attribute_id
- entity_type_id: for the entity type ID
- attribute_code: A unique, human readable name
- attribute_model: Optional model. Unspecified defaults to Magento\Eav\Model\Entity\Attribute
- backend_model: Optional backend model. Unspecified defaults to Magento\Eav\Model\Entity\Attribute\Backend
- backend_type: One of static, varchar, datetime, int, text, decimal
- backend_table: Optional override for the value table
- frontend_model: Alternative frontend model. Unspecified defaults to Magento\Eav\Model\Entity\Attribute\Frontend\DefaultFrontend
- frontend_input: Input type for the admin
- frontend_label: Default label for the admin
- frontend_class: CSS class name for inputs
- is_required: client-side validation, and validated on import
- default_value: displayed if no value is specified
Setup scripts use Magento\Eav\Setup\EavSetup, providing:
- addAttribute($entityType, $attributeCode, $dataArray)
- updateAttribute($entityType, $attributeCode, $field, $value)
- Fields are mapped using Magento\Eav\Model\Entity\Setup\PropertyMapperInterface::map()

Magento\Eav\Model\Config provides
- getAttribute($entityType, $attributeCode) returns an attribute instance
- getEntityType($entityTypeCode) returns an entity type instance