Doctrine 2 - Persist Entity with Joined Table's Foreign Key Opposed to Foreign Entity

I'm trying to persist a TradeEntity. A TradeEntity has a OneToOne relationship with a CurrencyEntity.

  /**
    * @ORM\OneToOne(targetEntity="Repositories\Currency\CurrencyEntity")
    * @ORM\JoinColumn(name="currency", referencedColumnName="id")
    *
    * @var CurrencyEntity
    */
    protected $currency;

I have recieved a CurrencyEntity from another object which I'm trying to insert in this new TradeEntity and persist it to the database but get an exception:

Type: Doctrine\ORM\ORMInvalidArgumentException
Message: Expected value of type "Repositories\Currency\CurrencyEntity" 
for association field "Repositories\Trade\TradeEntity#$currency", got "integer" instead.

Is there no other way of me persisting TradeEntity without fetching the CurrencyEntity from the database and setting it that way?