Symfony2 OneToOne relationship becomes either a Unique index or a foreign key?
I'm taking my first steps in Symfony2 entity relations.
I have an entity installation, which each has one meter, and one monitor.

This translates to a uni-directional relationship, which I defined as such:



        /**
         *
         * @ORM\OneToOne(targetEntity="InfoMeter")
         * @ORM\JoinColumn(name="meterid", referencedColumnName="id")
         */
        private $meter;  
    
        /**
         *
         * @ORM\OneToOne(targetEntity="InstallationsRtu")
         * @ORM\JoinColumn(name="monitorid", referencedColumnName="id")
         */
        private $monitor;


Each monitor can only be assigned to one installation.
Each meter can be assigned to multiple installations.

When I update my database (app/console doctrine:schema:update --force), there are two outcomes.  
In case of the monitor:  
Everything goes alright, schema gets updated with a keyname which is prefixed by 'UNIQ_'.

In case of the meter:
I get the following error

    PDOException]                                                                                             
      SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '1' for key 'UNIQ_43D26968860BE41D'

When I look at the table structure after this error occured, I can't find that mentioned constraint, but I do find FK_43D26968860BE41D, i.e. the same, but prefixed with 'FK'.

In the installation table, I now have these listed:

    Keyname	                Type	Unique	Packed	Field	  Cardinality
    PRIMARY	                BTREE	Yes	No	id	  2	
    UNIQ_43D26968701EC1AB	BTREE	Yes	No	monitorid 2		
    FK_43D26968860BE41D	BTREE	No	No	meterid	  2

So one saying 'Unique=Yes', and the other saying 'Unique=No'.

To arrive at my question:  
How can I decide whether it is a UNIQ index or a FK index? 
I assume that Doctrine saw that currently each monitorid is unique in the installation table, but that each meterid occurs several times in the installation table.   
Hence it went with UNIQ for the first, and FK for the latter. But can I control this somehow? 
Symfony2 OneToOne relationship becomes either a Unique index or a foreign key?
===

I'm taking my first steps in Symfony2 entity relations.
I have an entity installation, which each has one meter, and one monitor.

This translates to a uni-directional relationship, which I defined as such:



        /**
         *
         * @ORM\OneToOne(targetEntity="InfoMeter")
         * @ORM\JoinColumn(name="meterid", referencedColumnName="id")
         */
        private $meter;  
    
        /**
         *
         * @ORM\OneToOne(targetEntity="InstallationsRtu")
         * @ORM\JoinColumn(name="monitorid", referencedColumnName="id")
         */
        private $monitor;


Each monitor can only be assigned to one installation.
Each meter can be assigned to multiple installations.

When I update my database (app/console doctrine:schema:update --force), there are two outcomes.  
In case of the monitor:  
Everything goes alright, schema gets updated with a keyname which is prefixed by 'UNIQ_'.

In case of the meter:
I get the following error

    PDOException]                                                                                             
      SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '1' for key 'UNIQ_43D26968860BE41D'

When I look at the table structure after this error occured, I can't find that mentioned constraint, but I do find FK_43D26968860BE41D, i.e. the same, but prefixed with 'FK'.

In the installation table, I now have these listed:

    Keyname	                Type	Unique	Packed	Field	  Cardinality
    PRIMARY	                BTREE	Yes	No	id	  2	
    UNIQ_43D26968701EC1AB	BTREE	Yes	No	monitorid 2		
    FK_43D26968860BE41D	BTREE	No	No	meterid	  2

So one saying 'Unique=Yes', and the other saying 'Unique=No'.

To arrive at my question:  
How can I decide whether it is a UNIQ index or a FK index? 
I assume that Doctrine saw that currently each monitorid is unique in the installation table, but that each meterid occurs several times in the installation table.   
Hence it went with UNIQ for the first, and FK for the latter. But can I control this somehow? 