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4.0 |
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Database normalization is a process where data is split into different tables and links are created between those tables, in order to increase flexibility, reduce data redundancy and improve data integrity. Relationships are defined in the initialize
method of each model.
The following types of relationships are available: - one to one
hasOne(
string|array $fields,
string $referenceModel,
string|array $referencedFields,
array $options = null
)
hasOneThrough(
string|array $fields,
string $intermediateModel,
string|array $intermediateFields,
string|array $intermediateReferencedFields,
string $referenceModel,
string|array $referencedFields,
array $options = null
)
-
one to many
hasMany( string|array $fields, string $referenceModel, string|array $referencedFields, array options = null )
-
many to one
belongsTo( string|array $fields, string $referenceModel, string|array $referencedFields, array options = null )
-
many to many
hasManyToMany( string|array $fields, string $intermediateModel, string|array $intermediateFields, string|array $intermediateReferencedFields, string $referenceModel, string|array $referencedFields, array $options = null )
Relationships can be unidirectional or bidirectional, and each can be simple (a one to one model) or more complex (a combination of models). The model manager manages foreign key constraints for these relationships, the definition of these helps referential integrity as well as easy and fast access of related records to a model. Through the implementation of relations, it is easy to access data in related models from the source model easily and in a uniform way.
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Invoices extends Model
{
public function initialize()
{
$this->hasOne(
'inv_cst_id',
Customers::class,
'cst_id',
[
'alias' => 'customers',
'reusable' => true,
]
);
}
}
Unidirectional relations are those that are generated in relation to one another but not vice versa.
The bidirectional relations build relationships in both models and each model defines the inverse relationship of the other.
In Phalcon, relationships must be defined in the initialize()
method of a model. The methods belongsTo()
, hasMany()
, hasManyToMany()
, hasOne()
and hasOneThrough()
, define the relationship between one or more fields from the current model to fields in another model. Each of these methods requires 3 parameters:
- local fields
- referenced model
- referenced fields
Method | Description |
---|---|
belongsTo |
Defines a n-1 relationship |
hasMany |
Defines a 1-n relationship |
hasManyToMany |
Defines a n-n relationship |
hasOne |
Defines a 1-1 relationship |
hasOneThrough |
Defines a 1-1 relationship |
The following schema shows 3 tables whose relations will serve us as an example regarding relationships:
create table co_invoices
(
inv_id int(10) auto_increment primary key,
inv_cst_id int(10) null,
inv_status_flag tinyint(1) null,
inv_title varchar(100) null,
inv_total float(10, 2) null,
inv_created_at datetime null
);
create table co_invoices_x_products
(
ixp_inv_id int(10),
inv_prd_id int(10)
);
create table co_products
(
prd_id int(10) auto_increment primary key,
prd_title varchar(100) null,
prd_price float(10, 2) null
);
- The model
Invoices
has manyInvoicesProducts
. - The model
Products
has manyInvoicesProducts
. - The model
InvoicesProducts
belongs to bothInvoices
andProducts
models as a many-to-one relation. - The model
Invoices
has a relation many-to-many toProducts
throughInvoicesProducts
.
The models with their relations could be implemented as follows:
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Invoices extends Model
{
public $inv_id;
public $inv_cst_id;
public $inv_status_flag;
public $inv_title;
public $inv_total;
public $inv_created_at;
public function initialize()
{
$this->hasManyToMany(
'inv_id',
InvoicesProducts::class,
'ixp_inv_id',
'ixp_prd_id',
Products::class,
'prd_id',
[
'reusable' => true,
'alias' => 'products',
]
);
$this->hasMany(
'inv_id',
InvoicesProducts::class,
'ixp_inv_id',
[
'reusable' => true,
'alias' => 'invoicesProducts'
]
);
}
}
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class InvoicesProducts extends Model
{
public $ixp_inv_id;
public $ixp_prd_id;
public function initialize()
{
$this->belongsTo(
'ixp_inv_id',
Invoices::class,
'inv_id',
[
'reusable' => true,
'alias' => 'invoice'
]
);
$this->belongsTo(
'ixp_prd_id',
Products::class,
'prd_id',
[
'reusable' => true,
'alias' => 'product'
]
);
}
}
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Products extends Model
{
public $prd_id;
public $prd_title;
public $prd_price;
public $prd_created_at;
public function initialize()
{
// To the intermediate table
$this->hasMany(
'prd_id',
InvoicesProducts::class,
'ixp_prd_id'
);
// Many to many -> Invoices
$this->hasManyToMany(
'prd_id',
InvoicesProducts::class,
'ixp_prd_id',
'ixp_inv_id',
Invoices::class,
'inv_id',
[
'reusable' => true,
'alias' => 'invoices',
]
);
}
}
The first parameter indicates the field of the local model used in the relationship; the second indicates the name of the referenced model, and the third the field name in the referenced model. You could also use arrays to define multiple fields in the relationship.
Many to many relationships require 3 models and define the attributes involved in the relationship:
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Invoices extends Model
{
public $inv_id;
public $inv_cst_id;
public $inv_status_flag;
public $inv_title;
public $inv_total;
public $inv_created_at;
public function initialize()
{
$this->hasManyToMany(
'inv_id',
InvoicesProducts::class,
'ixp_inv_id',
'ixp_prd_id',
Products::class,
'prd_id',
[
'reusable' => true,
'alias' => 'products',
]
);
}
}
Depending on the needs of our application we might want to store data in one table, that describe different behaviors. For instance, you might want to only have a table called co_customers
which has a field cst_status_flag
describing the status of the customer (e.g. active, inactive, etc.).
Using relationships, you can get only those Customers
that relate to our Invoices
that have a certain cst_status_flag
. Defining that constraint in the relationship allows you to let the model do all the work.
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Invoices extends Model
{
public $inv_id;
public $inv_cst_id;
public $inv_status_flag;
public $inv_title;
public $inv_total;
public $inv_created_at;
public function initialize()
{
$this->hasMany(
'inv_cst_id',
Customers::class,
'cst_id',
[
'reusable' => true,
'alias' => 'customersActive',
'params' => [
'conditions' => 'cst_status_flag = :status:',
'bind' => [
'status' => 1,
]
]
]
);
}
}
There are times, where relationships need to be defined on a combination of fields and not only one. Consider the following example:
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Products extends Model
{
public $prd_id;
public $prd_type_flag;
public $prd_name;
}
and
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Parts extends Model
{
public $par_id;
public $par_prd_id;
public $par_par_id;
public $par_type_flag;
public $par_name;
}
In the above we have a Products
model which has prd_id
, prd_type_flag
and prd_name
fields. The Parts
model contains par_id
, par_prd_id
, par_type_flag
and par_name
. The relationship exists based on the product unique id as well as the type.
Using the relationship options, as seen above, binding one field between the two models will not return the results we need. We can use an array with the necessary fields to define the relationship.
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Products extends Model
{
public $prd_id;
public $prd_type_flag;
public $prd_name;
public function initialize()
{
$this->hasOne(
[
'prd_id',
'prd_type_flag'
],
Parts::class,
[
'par_prd_id',
'par_type_flag'
],
[
'reusable' => true, // cache
'alias' => 'parts',
]
);
}
}
NOTE The field mappings in the relationship are one for one i.e. the first field of the source model array matches the first field of the target array etc. The field count must be identical in both source and target models. {: .alert .alert-info }
There are several ways that we can access the relationships of a model.
- Magic
__get
,__set
- Magic
get*
getRelated
You can use the magic method to access the relationship. Assigning an alias
to the relationship simplifies accessing the related data. The name of the property is the same as the one defined in the alias
.
<?php
$customer = Customers::findFirst(
[
'conditions' => 'cst_id = :customerId:',
'bind' => [
'customerId' => 1,
],
]
);
foreach ($customer->invoices as $invoice) {
echo $invoice->inv_title;
}
or for a many to many relationship (see models above):
<?php
$invoice = Invoices::findFirst(
[
'conditions' => 'inv_cst_id = :customerId:',
'bind' => [
'customerId' => 1,
],
]
);
foreach ($invoice->invoicesProducts as $product) {
echo $invoice->product->prd_name;
}
foreach ($invoice->products as $product) {
echo $invoice->prd_name;
}
Using the magic __get
allows you to access the relationship directly but does not offer additional functionality such as filtering or ordering on the relationship.
You can access the same relationship by using a getter method, starting with get and using the name of the relationship.
<?php
$customer = Customers::findFirst(
[
'conditions' => 'cst_id = :customerId:',
'bind' => [
'customerId' => 1,
],
]
);
foreach ($customer->getInvoices() as $invoice) {
echo $invoice->inv_title;
}
or for a many to many relationship (see models above):
<?php
$invoice = Invoices::findFirst(
[
'conditions' => 'inv_cst_id = :customerId:',
'bind' => [
'customerId' => 1,
],
]
);
foreach ($invoice->getInvoiceProducts() as $product) {
echo $invoice->product->prd_name;
}
foreach ($invoice->getProducts() as $product) {
echo $invoice->prd_name;
}
This magic getter also allows us to perform certain operations when accessing the relationship such as ordering the relationship:
<?php
$invoice = Invoices::findFirst(
[
'conditions' => 'inv_cst_id = :customerId:',
'bind' => [
'customerId' => 1,
],
]
);
$products = $invoice->getProducts(
[
'order' => 'prd_name',
]
);
foreach ($products as $product) {
echo $invoice->prd_name;
}
You can also add additional conditionals in the relationship:
<?php
$invoice = Invoices::findFirst(
[
'conditions' => 'inv_cst_id = :customerId:',
'bind' => [
'customerId' => 1,
],
]
);
$products = $invoice->getProducts(
[
'prd_created_at = :date:',
'bind' => [
'date' => '2019-12-25',
],
]
);
foreach ($products as $product) {
echo $invoice->prd_name;
}
To get the same records manually:
<?php
$invoice = Invoices::findFirst(
[
'conditions' => 'inv_cst_id = :customerId:',
'bind' => [
'customerId' => 1,
],
]
);
$invoicesProducts = InvoicesProducts::find(
[
'conditions' => 'ixp_inv_id = :invoiceId:',
'bind' => [
'invoiceId' => $invoice->inv_id,
],
]
);
$productIds = [];
foreach ($invoicesProducts as $intermediate) {
$productIds[] = $intermediate->ixp_prd_id;
}
$products = Products::find(
[
'conditions' => 'prd_id IN ({array:productIds})',
'bind' => [
'productIds' => $productIds,,
],
]
);
foreach ($products as $product) {
echo $invoice->prd_name;
}
The prefix get
is used to find()
/findFirst()
related records.
Type | Implicit Method | Returns |
---|---|---|
Belongs-To | findFirst |
Model instance of the related record directly |
Has-One | findFirst |
Model instance of the related record directly |
Has-One-Through | findFirst |
Model instance of the related record directly |
Has-Many | find |
Collection of model instances of the referenced model |
Has-Many-to-Many | (complex query) | Collection of model instances of the referenced model (inner join ) |
You can also use the count
prefix to return an integer denoting the count of the related records:
<?php
$invoice = Invoices::findFirst(
[
'conditions' => 'inv_cst_id = :customerId:',
'bind' => [
'customerId' => 1,
],
]
);
echo $invoice->countProducts();
You can access the same relationship by using getRelated()
and defining which relationship you want to get.
<?php
$customer = Customers::findFirst(
[
'conditions' => 'cst_id = :customerId:',
'bind' => [
'customerId' => 1,
],
]
);
foreach ($customer->getRelated('invoices') as $invoice) {
echo $invoice->inv_title;
}
or for a many to many relationship (see models above):
<?php
$invoice = Invoices::findFirst(
[
'conditions' => 'inv_cst_id = :customerId:',
'bind' => [
'customerId' => 1,
],
]
);
foreach ($invoice->getRelated('products') as $product) {
echo $invoice->prd_name;
}
The second parameter of getRelated()
is an array that offers additional options to be set such as filtering and ordering.
<?php
$invoice = Invoices::findFirst(
[
'conditions' => 'inv_cst_id = :customerId:',
'bind' => [
'customerId' => 1,
],
]
);
$products = $invoice->getRelated(
'products',
[
'prd_created_at = :date:',
'bind' => [
'date' => '2019-12-25',
],
]
);
foreach ($products as $product) {
echo $invoice->prd_name;
}
Accessing a relationship cam be achieved by using the name of the remote table. Due to naming conventions, this might not be that easy and could lead to confusion. As seen above, you can define an alias
to the relationship.
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Invoices extends Model
{
public $inv_id;
public $inv_cst_id;
public $inv_status_flag;
public $inv_title;
public $inv_total;
public $inv_created_at;
public function initialize()
{
$this->hasManyToMany(
'inv_id',
InvoicesProducts::class,
'ixp_inv_id',
'ixp_prd_id',
Products::class,
'prd_id'
);
}
}
With an alias:
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Invoices extends Model
{
public $inv_id;
public $inv_cst_id;
public $inv_status_flag;
public $inv_title;
public $inv_total;
public $inv_created_at;
public function initialize()
{
$this->hasManyToMany(
'inv_id',
InvoicesProducts::class,
'ixp_inv_id',
'ixp_prd_id',
Products::class,
'prd_id',
[
'reusable' => true,
'alias' => 'products',
]
);
}
}
If your table structure has self joins, you will not be able to access those relationships without aliases because you will be using the same model.
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Parts extends Model
{
public $par_id;
public $par_prd_id;
public $par_par_id;
public $par_type_flag;
public $par_name;
public function initialize()
{
$this->hasMany(
'par_id',
Invoices::class,
'par_par_id',
[
'reusable' => true,
'alias' => 'children',
]
);
$this->belongsTo(
'par_par_id',
Invoices::class,
'par_id',
[
'reusable' => true,
'alias' => 'parent',
]
);
}
}
In the example above, we have a Part
that has a relationship with one or more Part
objects. Each Part
can consist of other parts that construct it. As a result we end up with a self join relationship. For a telephone Part
we have the following children:
<?php
$phone = Parts::findFirst(....);
echo $phone->getChildren();
// --- Cover
// --- Battery
// --- Charger
and each of those parts has the telephone as a parent:
<?php
$charger = Parts::findFirst(....);
echo $phone->getParent();
// Phone
Accessing related data can significantly increase the number of queries in your database. You can reduce this load as much as possible, by utilizing the reusable
option in your relationship. Setting this option to true
will instruct Phalcon to cache the results of the relationship the first time it is accessed, so that subsequent calls to the same relationship can use the cached resultset and not request the data again from the database. This cache is active during the same request.
NOTE: You are encouraged to use the
reusable
option as often as possible in your relationships {: .alert .alert-info }
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Invoices extends Model
{
public function initialize()
{
$this->hasOne(
'inv_cst_id',
Customers::class,
'cst_id',
[
'alias' => 'customers',
'reusable' => true,
]
);
}
}
Most IDEs and editors with auto-completion capabilities can not detect the correct types when using magic getters (both methods and properties). To address this issue, you can use the class docblock that specifies what magic actions are available, helping the IDE to produce a better auto-completion:
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
/**
* Invoices model
*
* @property Simple|Products[] $products
* @method Simple|Products[] getProducts($parameters = null)
* @method integer countProducts()
*/
class Invoices extends Model
{
public $inv_id;
public $inv_cst_id;
public $inv_status_flag;
public $inv_title;
public $inv_total;
public $inv_created_at;
public function initialize()
{
$this->hasManyToMany(
'inv_id',
InvoicesProducts::class,
'ixp_inv_id',
'ixp_prd_id',
Products::class,
'prd_id',
[
'reusable' => true,
'alias' => 'products',
]
);
}
}
You can also create relationships based on conditionals. When querying based on the relationship the condition will be automatically appended to the query:
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Invoices extends Model
{
public $inv_id;
public $inv_cst_id;
public $inv_status_flag;
public $inv_title;
public $inv_total;
public $inv_created_at;
public function initialize()
{
$this->hasManyToMany(
'inv_id',
InvoicesProducts::class,
'ixp_inv_id',
'ixp_prd_id',
Products::class,
'prd_id',
[
'reusable' => true,
'alias' => 'products',
]
);
}
}
class Companies extends Model
{
public function initialize()
{
// All invoices relationship
$this->hasMany(
'id',
Invoices::class,
'inv_id',
[
'alias' => 'Invoices',
]
);
// Paid invoices relationship
$this->hasMany(
'id',
Invoices::class,
'inv_id',
[
'alias' => 'InvoicesPaid',
'params' => [
'conditions' => "inv_status = 'paid'",
],
]
);
// Unpaid invoices relationship + bound parameters
$this->hasMany(
'id',
Invoices::class,
'inv_id',
[
'alias' => 'InvoicesUnpaid',
'params' => [
'conditions' => "inv_status <> :status:",
'bind' => [
'status' => 'unpaid',
],
],
]
);
}
}
Additionally, you can use the parameters of getInvoices()
or getRelated()
on the model, to further filter or order your relationship:
<?php
$company = Companies::findFirst(
[
'conditions' => 'id = :id:',
'bind' => [
'id' => 1,
],
]
);
*
$unpaidInvoices = $company->InvoicesUnpaid;
$unpaidInvoices = $company->getInvoicesUnpaid();
$unpaidInvoices = $company->getRelated('InvoicesUnpaid');
$unpaidInvoices = $company->getRelated(
'Invoices',
[
'conditions' => "inv_status = 'paid'",
]
);
// Also ordered
$unpaidInvoices = $company->getRelated(
'Invoices',
[
'conditions' => "inv_status = 'paid'",
'order' => 'inv_created_date ASC',
]
);
By default, relationships do not have any constraints attached to them, to check related data when adding, updating or deleting records. You can however attach validations to your relationships, to ensure integrity of data. This can be done with the last parameter of the relationship related method.
The cross table InvoicesProducts
can be slightly changed to demonstrate this functionality:
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class InvoicesProducts extends Model
{
public $ixp_inv_id;
public $ixp_prd_id;
public function initialize()
{
$this->belongsTo(
'ixp_inv_id',
Invoices::class,
'inv_id',
[
'alias' => 'invoice',
'foreignKey' => true,
'reusable' => true,
]
);
$this->belongsTo(
'ixp_prd_id',
Products::class,
'prd_id',
[
'alias' => 'product',
'foreignKey' => [
'message' => 'The prd_id does not exist ' .
'in the Products model',
],
'reusable' => true,
]
);
}
}
If you alter a belongsTo()
relationship to act as foreign key, it will validate that the values inserted/updated on those fields have reference valid ids in the respective models. Similarly, if a hasMany()
/hasOne()
is changed to define the foreignKey
, it will validate that records can or cannot if the record has related data.
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class Products extends Model
{
public $prd_id;
public $prd_title;
public $prd_price;
public $prd_created_at;
public function initialize()
{
$this->hasMany(
'prd_id',
Products::class,
'ixp_prd_id',
[
'foreignKey' => [
'message' => 'The product cannot be deleted ' .
'because there are invoices ' .
'attached to it',
],
]
);
}
}
A virtual foreign key can be set up to allow null values as follows:
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
class InvoicesProducts extends Model
{
public $ixp_inv_id;
public $ixp_prd_id;
public function initialize()
{
$this->belongsTo(
'ixp_inv_id',
Invoices::class,
'inv_id',
[
'alias' => 'invoice',
'foreignKey' => true,
'reusable' => true,
]
);
$this->belongsTo(
'ixp_prd_id',
Products::class,
'prd_id',
[
'alias' => 'product',
'foreignKey' => [
'allowNulls' => true,
'message' => 'The prd_id does not exist ' .
'in the Products model',
],
'reusable' => true,
]
);
}
}
Relationships that act as virtual foreign keys by default restrict the creation/update/deletion of records to maintain the integrity of data. You can define these constraints that mimic the RDBMS functionality for CASCADE
and RESTRICT
by using the action
option in foreignKey
. The Phalcon\Mvc\Model\Relation underlying object offers two constants:
Relation::ACTION_CASCADE
Relation::ACTION_RESTRICT
<?php
namespace MyApp\Models;
use Phalcon\Mvc\Model;
use Phalcon\Mvc\Model\Relation;
class Products extends Model
{
public $prd_id;
public $prd_title;
public $prd_price;
public $prd_created_at;
public function initialize()
{
$this->hasMany(
'prd_id',
Products::class,
'ixp_prd_id',
[
'foreignKey' => [
'action' => Relation::ACTION_CASCADE,
],
]
);
}
}
The code above allows you to delete all the related record if the primary record is deleted (cascade delete).
You can perform operations using relationships, if a resultset returns complete objects.
Magic properties can be used to store a record and its related properties:
<?php
// Create an artist
$artist = new Artists();
$artist->name = 'Shinichi Osawa';
$artist->country = 'Japan';
// Create an album
$album = new Albums();
$album->name = 'The One';
$album->artist = $artist; // Assign the artist
$album->year = 2008;
// Save both records
$album->save();
Saving a record and its related records in a has-many relation:
<?php
$customer = Customers::findFirst(
[
'conditions' => 'cst_id = :customerId:',
'bind' => [
'customerId' => 1,
]
]
);
$invoice1 = new Invoices();
$invoice1-> inv_status_flag = 0;
$invoice1-> inv_title = 'Invoice for ACME Inc. #1';
$invoice1-> inv_total = 100;
$invoice1-> inv_created_at = time();
$invoice2 = new Invoices();
$invoice2-> inv_status_flag = 0;
$invoice2-> inv_title = 'Invoice for ACME Inc. #2';
$invoice2-> inv_total = 200;
$invoice2-> inv_created_at = time();
$customer->invoices = [
$invoice1,
$invoice2
];
$customer->save();
The code above gets a customer from our database. Two invoices are created and assigned to the invoices
relationship of the customer as an array. The customer record is then saved, which also saves the two invoices in the database and links them to the customer.
Although the syntax above is very handy, it is not always ideal to use it, especially when updating related records. Phalcon does not know which records need to be added or removed using an update, and as a result it will perform a replace. In update situations, it is better to control the data yourself vs. leaving it to the framework to do that.
Saving data with the above syntax will implicitly create a transaction and commit it if all goes well. Messages generated during the save process of the whole transaction will be passed back to the user for more information.
NOTE: Adding related entities by overloading the following methods/events is not possible:
Phalcon\Mvc\Model::beforeSave()
Phalcon\Mvc\Model::beforeCreate()
Phalcon\Mvc\Model::beforeUpdate()
{: .alert .alert-warning }
You need to overload Phalcon\Mvc\Model::save()
for this to work from within a model.
Instead of doing this:
<?php
$invoices = $customer->getInvoices();
foreach ($invoices as $invoice) {
$invoice->inv_total = 100;
$invoice->inv_updated_at = time();
if (false === $invoice->update()) {
$messages = $invoice->getMessages();
foreach ($messages as $message) {
echo $message;
}
break;
}
}
you can do this:
<?php
$customer->getInvoices()->update(
[
'inv_total' => 100,
'inv_updated_at' => time(),
]
);
update
also accepts an anonymous function to filter what records must be updated:
<?php
$data = [
'inv_total' => 100,
'inv_updated_at' => time(),
];
$customer->getInvoices()->update(
$data,
function ($invoice) {
return ($invoice->inv_cst_id !== 1);
}
);
Instead of doing this:
<?php
$invoices = $customer->getInvoices();
foreach ($invoices as $invoice) {
if (false === $invoice->delete()) {
$messages = $invoice->getMessages();
foreach ($messages as $message) {
echo $message;
}
break;
}
}
you can do this:
<?php
$customer->getInvoices()->delete();
delete()
also accepts an anonymous function to filter what records must be deleted:
<?php
$customer->getInvoices()->delete(
function ($invoice) {
return ($invoice->inv_total >= 0);
}
);