Magento 2 - Custom Repository does not create new entity

Question

I create a custom entity and repository. All work well, but the POST API route does not create new entities. But if I call the PUT API route to change a property, it works well. Why my custom repository doesn't create new entities?

webapi.xml

<?xml version="1.0"?>
<routes xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Webapi:etc/webapi.xsd">
    <route url="/V1/shipment_methods" method="GET">
        <service class="MyVendorName\MyModuleName\Api\ShipmentMethodRepositoryInterface" method="getList"/>
        <resources>
            <resource ref="anonymous"/>
        </resources>
    </route>
    <route url="/V1/shipment_methods/:code" method="GET">
        <service class="MyVendorName\MyModuleName\Api\ShipmentMethodRepositoryInterface" method="getByCode"/>
        <resources>
            <resource ref="MyVendorName_MyModuleName::shipment_method"/>
        </resources>
    </route>
    <route url="/V1/shipment_methods" method="POST">
        <service class="MyVendorName\MyModuleName\Api\ShipmentMethodRepositoryInterface" method="save"/>
        <resources>
            <resource ref="MyVendorName_MyModuleName::shipment_method_save"/>
        </resources>
    </route>
    <route url="/V1/shipment_methods/:code" method="PUT">
        <service class="MyVendorName\MyModuleName\Api\ShipmentMethodRepositoryInterface" method="save"/>
        <resources>
            <resource ref="MyVendorName_MyModuleName::shipment_method_save"/>
        </resources>
    </route>
    <route url="/V1/shipment_methods" method="DELETE">
        <service class="MyVendorName\MyModuleName\Api\ShipmentMethodRepositoryInterface" method="delete"/>
        <resources>
            <resource ref="MyVendorName_MyModuleName::shipment_method_delete"/>
        </resources>
    </route>
    <route url="/V1/shipment_methods/:code" method="DELETE">
        <service class="MyVendorName\MyModuleName\Api\ShipmentMethodRepositoryInterface" method="deleteByCode"/>
        <resources>
            <resource ref="MyVendorName_MyModuleName::shipment_method_delete"/>
        </resources>
    </route>
</routes>

ShipmentMethodRepository

<?php
declare(strict_types=1);

namespace MyVendorName\MyModuleName\Model;

use MyVendorName\MyModuleName\Api\Data\ShipmentMethodInterface;
use MyVendorName\MyModuleName\Api\Data\ShipmentMethodSearchResultsInterface;
use MyVendorName\MyModuleName\Api\ShipmentMethodRepositoryInterface;
use MyVendorName\MyModuleName\Model\ResourceModel\ShipmentMethod as ShipmentMethodResourceModel;
use Magento\Framework\Api\SearchCriteriaInterface;
use Magento\Framework\Exception\CouldNotDeleteException;
use Magento\Framework\Exception\CouldNotSaveException;
use Magento\Framework\Exception\NoSuchEntityException;

class ShipmentMethodRepository implements ShipmentMethodRepositoryInterface
{
    /**
     * @var ShipmentMethodFactory
     */
    private $shipmentMethodFactory;

    /**
     * @var ShipmentMethodResourceModel
     */
    private $shipmentMethodResourceModel;

    /**
     * ShipmentMethodRepository constructor.
     * @param ShipmentMethodFactory $shipmentMethodFactory
     * @param ShipmentMethodResourceModel $shipmentMethodResourceModel
     */
    public function __construct(
        ShipmentMethodFactory $shipmentMethodFactory,
        ShipmentMethodResourceModel $shipmentMethodResourceModel
    ) {
        $this->shipmentMethodFactory = $shipmentMethodFactory;
        $this->shipmentMethodResourceModel = $shipmentMethodResourceModel;
    }

    /**
     * Retrieve shipment methods which match a specified criteria
     * @param \Magento\Framework\Api\SearchCriteriaInterface $searchCriteria
     * @return \MyVendorName\MyModuleName\Api\Data\ShipmentMethodSearchResultsInterface
     */
    public function getList(SearchCriteriaInterface $searchCriteria): ShipmentMethodSearchResultsInterface
    {
        // TODO: Implement getList() method.
    }

    /**
     * Get shipment method by code
     * @param string $code
     * @return \MyVendorName\MyModuleName\Api\Data\ShipmentMethodInterface
     * @throws \Magento\Framework\Exception\NoSuchEntityException
     */
    public function getByCode(string $code): ShipmentMethodInterface
    {
        $shipmentMethod = $this->shipmentMethodFactory->create();
        $this->shipmentMethodResourceModel->load($shipmentMethod, $code);

        if (!$shipmentMethod->getCode()) {
            throw new NoSuchEntityException(__('Shipment method with code %1 does not exist.', $code));
        }

        return $shipmentMethod;
    }

    /**
     * Create or update a shipment method
     * @param \MyVendorName\MyModuleName\Api\Data\ShipmentMethodInterface $shipmentMethod
     * @return \MyVendorName\MyModuleName\Api\Data\ShipmentMethodInterface
     * @throws \Magento\Framework\Exception\CouldNotSaveException
     */
    public function save(ShipmentMethodInterface $shipmentMethod): ShipmentMethodInterface
    {
        try {
            $this->shipmentMethodResourceModel->save($shipmentMethod);
        } catch (\Exception $e) {
            throw new CouldNotSaveException(__($e->getMessage()));
        }

        return $shipmentMethod;
    }

    /**
     * Delete shipment method
     * @param \MyVendorName\MyModuleName\Api\Data\ShipmentMethodInterface $shipmentMethod
     * @return bool
     * @throws \Magento\Framework\Exception\CouldNotDeleteException
     */
    public function delete(ShipmentMethodInterface $shipmentMethod): bool
    {
        try {
            $this->shipmentMethodResourceModel->delete($shipmentMethod);
        } catch (\Exception $e) {
            throw new CouldNotDeleteException(__($e->getMessage()));
        }

        return true;
    }

    /**
     * Delete shipment method by code
     * @param string $code
     * @return bool
     * @throws \Magento\Framework\Exception\NoSuchEntityException
     * @throws \Magento\Framework\Exception\CouldNotDeleteException
     */
    public function deleteByCode(string $code): bool
    {
        return $this->delete($this->getByCode($code));
    }
}

di.xml

<preference for="MyVendorName\MyModuleName\Api\Data\ShipmentMethodInterface" type="MyVendorName\MyModuleName\Model\ShipmentMethod"/>
<preference for="MyVendorName\MyModuleName\Api\ShipmentMethodRepositoryInterface" type="MyVendorName\MyModuleName\Model\ShipmentMethodRepository"/>

Model\ShipmentMethod

<?php
declare(strict_types=1);

namespace MyVendorName\MyModuleName\Model;

use MyVendorName\MyModuleName\Api\Data\ShipmentMethodInterface;
use MyVendorName\MyModuleName\Model\ResourceModel\ShipmentMethod as ShipmentMethodResourceModel;
use Magento\Framework\Model\AbstractModel;

class ShipmentMethod extends AbstractModel implements ShipmentMethodInterface
{
    /**
     * {@inheritDoc}
     */
    protected function _construct(): void
    {
        $this->_init(ShipmentMethodResourceModel::class);
    }

    /**
     * {@inheritDoc}
     */
    public function getCode(): string
    {
        return (string)$this->getData(self::CODE);
    }

    /**
     * {@inheritDoc}
     */
    public function setCode(string $code): ShipmentMethodInterface
    {
        $this->setData(self::CODE, $code);

        return $this;
    }

    /**
     * {@inheritDoc}
     */
    public function getDescription(): string
    {
        return (string)$this->getData(self::DESCRIPTION);
    }

    /**
     * {@inheritDoc}
     */
    public function setDescription(string $description): ShipmentMethodInterface
    {
        $this->setData(self::DESCRIPTION, $description);

        return $this;
    }

    /**
     * {@inheritDoc}
     */
    public function getCourierCode(): string
    {
        return (string)$this->getData(self::COURIER_CODE);
    }

    /**
     * {@inheritDoc}
     */
    public function setCourierCode(string $courierCode): ShipmentMethodInterface
    {
        $this->setData(self::COURIER_CODE, $courierCode);

        return $this;
    }

    /**
     * {@inheritDoc}
     */
    public function getServiceCode(): string
    {
        return (string)$this->getData(self::SERVICE_CODE);
    }

    /**
     * {@inheritDoc}
     */
    public function setServiceCode(string $serviceCode): ShipmentMethodInterface
    {
        $this->setData(self::SERVICE_CODE, $serviceCode);

        return $this;
    }

    /**
     * {@inheritDoc}
     */
    public function getIsExpress(): bool
    {
        return (bool)$this->getData(self::IS_EXPRESS);
    }

    /**
     * {@inheritDoc}
     */
    public function setIsExpress(bool $isExpress): ShipmentMethodInterface
    {
        $this->setData(self::IS_EXPRESS, $isExpress);

        return $this;
    }

    /**
     * {@inheritDoc}
     */
    public function getTiming(): string
    {
        return (string)$this->getData(self::TIMING);
    }

    /**
     * {@inheritDoc}
     */
    public function setTiming(string $timing): ShipmentMethodInterface
    {
        $this->setData(self::TIMING, $timing);

        return $this;
    }
}

Model\ResourceModel\ShipmentMethod

<?php
declare(strict_types=1);

namespace MyVendorName\MyModuleName\Shipment\Model\ResourceModel;

use Magento\Framework\Model\ResourceModel\Db\AbstractDb;

class ShipmentMethod extends AbstractDb
{
    public const TABLE_NAME = 'my_shipment_method';

    /**
     * {@inheritDoc}
     */
    protected function _construct(): void
    {
        $this->_init(self::TABLE_NAME, 'code');
    }
}

Answer 1

I found the solution through this post how-set-resource-model-for-not-primary-ai :). In nutshell, because my primary key is not auto-increment, the resource model fails the save method for new entities. To solve the problem you should set protected $_isPkAutoIncrement = false; inside your resource model class