PHP - Sql Injection Issue

I need to create an entity which models the connection between a PHP server and another device so that a web app can change the entity's properties which in turn will update the server DB as well as the other device.  A little background information for context is as follows:

When a socket clients connects to the PHP server, it will register by providing its GUID, and in turn the server will query its DB to identify the specific client.  The client has various other properties associated with the socket connection such as reconnect_timeout, response_timeout, etc, and the associated values will also be stored in the server's DB.

While all socket clients use the same approach to communicate to the PHP server, several "flavors" of socket clients exists which use a specific protocol (Modbus/RTU, Modbus/IP, ControlNet, BACnet/IP, BACnet/MSTP, KNX, DALI) to communicate to downstream devices.  Based on the used protocol, there will be different properties as well as different methods (i.e. some protocols allow one to query the device to retrieve a list of available data).

To create the entity using inheritance, I would likely do so whe

class ModbusRtuSocketClient extends ModbusSocketClient (which extends SocketClient)
class ModbusIpSocketClient extends ModbusSocketClient (which extends SocketClient)
class ControlNetSocketClient extends SocketClient
etc..

But instead of doing so by using inheritance, I am thinking that I should do so through injection.  For instance, I create an object called SocketClient which just deals with that scope of work and is protocol agnostic.  I also create a second object which deals with a given protocol such as ModbusRtuProtocol extends ModbusProtocol extends Protocol.  I then do one of the following:

$entity = new SocketClient(new ModbusRtuProtocol());
//or
$entity = new ModbusRtuProtocol(new SocketClient());

//and do
$entity->setSomeSocketClientProperty(123);
$entity->getProperty()->setSomeSpecificProtocolProperty(321);
$entity->updateEndDevice();
$entityManager->persist($entity);
$entityManager->flush();

//or do
$values=$entity->queryDevice();

The first approach "seems" right, but I am not sure.  One concern is I cannot create a standard interface to govern all protocols because the methods are so protocol specific (maybe I need to think harder how to make a standard interface?).   Any recommendations where I should be going on this?

PS.  If you think I shouldn't be doing so through injection but through inheritance, please advise.

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