UPGRADE_TO_2_0

# Upgrade from 2.0-ALPHA4 to 2.0-BETA1

## New inversedBy attribute

It is now *mandatory* that the owning side of a bidirectional association specifies the
'inversedBy' attribute that points to the name of the field on the inverse side that completes
the association. Example:

    [php]
    // BEFORE (ALPHA4 AND EARLIER)
    class User
    {
        //...
        /** @OneToOne(targetEntity="Address", mappedBy="user") */
        private $address;
        //...
    }
    class Address
    {
        //...
        /** @OneToOne(targetEntity="User") */
        private $user;
        //...
    }
    
    // SINCE BETA1
    // User class DOES NOT CHANGE
    class Address
    {
        //...
        /** @OneToOne(targetEntity="User", inversedBy="address") */
        private $user;
        //...
    }
    
Thus, the inversedBy attribute is the counterpart to the mappedBy attribute. This change
was necessary to enable some simplifications and further performance improvements. We
apologize for the inconvenience.

## Default Property for Field Mappings

The "default" option for database column defaults has been removed. If desired, database column defaults can
be implemented by using the columnDefinition attribute of the @Column annotation (or the approriate XML and YAML equivalents).
Prefer PHP default values, if possible.

## Partial Objects

[TBD: New syntax, results, etc.]

## XML Mapping Driver

The 'inheritance-type' attribute changed to take last bit of ClassMetadata constant names, i.e.
NONE, SINGLE_TABLE, INHERITANCE_TYPE_JOINED

## YAML Mapping Driver

The way to specify lifecycle callbacks in YAML Mapping driver was changed to allow for multiple callbacks
per event. The Old syntax ways:

    [yaml]
    lifecycleCallbacks:
      doStuffOnPrePersist: prePersist
      doStuffOnPostPersist: postPersist

The new syntax is:

    [yaml]
    lifecycleCallbacks:
      prePersist: [ doStuffOnPrePersist, doOtherStuffOnPrePersistToo ]
      postPersist: [ doStuffOnPostPersist ]

## PreUpdate Event Listeners

Event Listeners listening to the 'preUpdate' event can only affect the primitive values of entity changesets
by using the API on the `PreUpdateEventArgs` instance passed to the preUpdate listener method. Any changes
to the state of the entitys properties won't affect the database UPDATE statement anymore. This gives drastic
performance benefits for the preUpdate event.