Modelling
Messaging and Ecotone In Depth
Method Invocation
Method Invocation PHP
Injecting arguments
Ecotone inject arguments to invoked method based on Parameter Converters.
Parameter converters tells Ecotone how to resolve specific parameter and what kind of argument is it expecting. 1
#[CommandHandler]
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public function changePrice(
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#[Payload] ChangeProductPriceCommand $command,
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#[Headers] array $metadata,
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#[Reference] UserService $userService
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) : void
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{
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$userId = $metadata["userId"];
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if (!$userService->isAdmin($userId)) {
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throw new \InvalidArgumentException("You need to be administrator in order to register new product");
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}
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​
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$this->price = $command->getPrice();
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}
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Our Command Handler method declaration is built from three parameters.
Ecotone does resolve parameters based on given attribute types.
Payload - Does inject payload of the message. In our case it will be the command itself
Headers - Does inject all headers as array.
Reference- Does inject service from Dependency Container. If referenceNamewhich is name of the service in the container is not given, then it will take the class name as default.Default Converters
Ecotone, if parameter converters are not passed provides default converters. - First parameter is always
Payload. - The second parameter, if is
arraythenHeadersconverter is taken - If class type hint is provided for parameter, then
Referenceconverter is picked - Otherwise, if no default converter can be applied exception will be thrown with information about missing parameter.
Our Command Handler can benefit from default converters, so we don't need to use any additional configuration.
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#[CommandHandler]
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public function changePrice(ChangeProductPriceCommand $command, array $metadata, UserService $userService) : void
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{
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$userId = $metadata["userId"];
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if (!$userService->isAdmin($userId)) {
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throw new \InvalidArgumentException("You need to be administrator in order to register new product");
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}
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​
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$this->price = $command->getPrice();
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}
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Parameter Converter Types
Payload Converter
Payload converter is responsible for passing payload of the message to given parameter.
It contains of two attributes:expression(Optional) - Allow for performing transformations before passing argument to parameter
Converting payload
Message's payload is not always the same type as expected in method declaration.
As in above example, we may expect:
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ChangeProductPriceCommand $command
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But the message may contains:
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{"payload": '{"productId": 123, "price": 100}', "headers": {"contentType": "application/json"}}
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The message may contains of special header
contentTypewhich describes content type of Message as media type. Based on this information, if payload of message is not compatible with parameter's type hint, Ecotone do the conversion.Thanks to conversion on the level of endpoint, Ecotone does not expect running
Command Bus with specific class instance. It may receive anything xml, json etc as long as Converter for specific Media Type is registered in the system.Expression
Expression does use of great feature of Symfony, called Expression Language. If you have not came across expression language yet, take few minutes to read about it.
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Payload(expression: "payload * 2")
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There are three types of variables available within expression.
payload- which is just payload of currently handled Messageheaders- contains of all headers available within Messagereference- which allow for retrieving service from Dependency Container and calling a method on it. The result of the expression will be passed to parameter after optional conversion.1Payload(expression:"reference('calculatingService').multiply(payload, 2)")Copied!
Headers Converter (Headers)
Headers converter is responsible for passing all headers of the message as array to given parameter. Header Converter (Header)
Header converter is responsible for passing specific header from message headers to given parameter.
It contains attributes:headerName(Required) - Allow for performing transformations before passing argument to parameterexpression- Allow for performing transformations before passing argument to parameter, same as in Payload expression​
Expression
Besides three types of variables available within expression just as with
Payload Expression, there is one more variable available value. Value holds chosen header by headerName attribute.Reference (Reference)
Reference converter is responsible for retrieving object from Dependency Container and passing it to given parameter.
It does contain attributes:referenceName(Optional) - Reference name of given object in Dependency Container. If not passed, then type hint of given parameter will be used.